Merge branch 'master' into Enterprise

2024-12-25 03:32:01 +00:00 · 2021-06-10 21:41:57 -04:00 · 2021-06-10 21:41:57 -04:00 · 8e0a6df03b
commit 8e0a6df03b
parent 2a6e9c5e8a 95a52a9f62
48 changed files with 1509 additions and 675 deletions
--- a/Components/9918/9918.cpp
+++ b/Components/9918/9918.cpp
@ -750,7 +750,7 @@ HalfCycles TMS9918::get_next_sequence_point() {
 	if(next_line_interrupt_row == -1) {
 		return generate_interrupts_ ?
 			half_cycles_before_internal_cycles(time_until_frame_interrupt) :
-			HalfCycles(-1);
+			HalfCycles::max();
 	}

 	// Figure out the number of internal cycles until the next line interrupt, which is the amount
--- a/Machines/AmstradCPC/AmstradCPC.cpp
+++ b/Machines/AmstradCPC/AmstradCPC.cpp
@ -787,45 +787,43 @@ template <bool has_fdc> class ConcreteMachine:
 			ay_.ay().set_port_handler(&key_state_);

 			// construct the list of necessary ROMs
-			const std::string machine_name = "AmstradCPC";
-			std::vector<ROMMachine::ROM> required_roms = {
-				ROMMachine::ROM(machine_name, "the Amstrad Disk Operating System", "amsdos.rom", 16*1024, 0x1fe22ecd)
-			};
-			std::string model_number;
-			uint32_t crcs[2];
+			bool has_amsdos = false;
+			ROM::Name firmware, basic;
+
 			switch(target.model) {
-				default:
-					model_number = "6128";
-					has_128k_ = true;
-					crcs[0] = 0x0219bb74;
-					crcs[1] = 0xca6af63d;
-				break;
 				case Analyser::Static::AmstradCPC::Target::Model::CPC464:
-					model_number = "464";
-					has_128k_ = false;
-					crcs[0] = 0x815752df;
-					crcs[1] = 0x7d9a3bac;
+					firmware = ROM::Name::CPC464Firmware;
+					basic = ROM::Name::CPC464BASIC;
 				break;
 				case Analyser::Static::AmstradCPC::Target::Model::CPC664:
-					model_number = "664";
-					has_128k_ = false;
-					crcs[0] = 0x3f5a6dc4;
-					crcs[1] = 0x32fee492;
+					firmware = ROM::Name::CPC664Firmware;
+					basic = ROM::Name::CPC664BASIC;
+					has_amsdos = true;
+				break;
+				default:
+					firmware = ROM::Name::CPC6128Firmware;
+					basic = ROM::Name::CPC6128BASIC;
+					has_amsdos = true;
 				break;
 			}
-			required_roms.emplace_back(machine_name, "the CPC " + model_number + " firmware", "os" + model_number + ".rom", 16*1024, crcs[0]);
-			required_roms.emplace_back(machine_name, "the CPC " + model_number + " BASIC ROM", "basic" + model_number + ".rom", 16*1024, crcs[1]);

-			// fetch and verify the ROMs
-			const auto roms = rom_fetcher(required_roms);
-
-			for(std::size_t index = 0; index < roms.size(); ++index) {
-				auto &data = roms[index];
-				if(!data) throw ROMMachine::Error::MissingROMs;
-				roms_[index] = std::move(*data);
-				roms_[index].resize(16384);
+			ROM::Request request = ROM::Request(firmware) && ROM::Request(basic);
+			if(has_amsdos) {
+				request = request && ROM::Request(ROM::Name::AMSDOS);
 			}

+			// Fetch and verify the ROMs.
+			auto roms = rom_fetcher(request);
+			if(!request.validate(roms)) {
+				throw ROMMachine::Error::MissingROMs;
+			}
+
+			if(has_amsdos) {
+				roms_[ROMType::AMSDOS] = roms.find(ROM::Name::AMSDOS)->second;
+			}
+			roms_[ROMType::OS] = roms.find(firmware)->second;
+			roms_[ROMType::BASIC] = roms.find(basic)->second;
+
 			// Establish default memory map
 			upper_rom_is_paged_ = true;
 			upper_rom_ = ROMType::BASIC;
--- a/Machines/Apple/AppleII/AppleII.cpp
+++ b/Machines/Apple/AppleII/AppleII.cpp
@ -377,49 +377,55 @@ template <Analyser::Static::AppleII::Target::Model model> class ConcreteMachine:

 			// Pick the required ROMs.
 			using Target = Analyser::Static::AppleII::Target;
-			const std::string machine_name = "AppleII";
-			std::vector<ROMMachine::ROM> rom_descriptions;
-			size_t rom_size = 12*1024;
+			ROM::Name character, system;
+
 			switch(target.model) {
 				default:
-					rom_descriptions.push_back(video_.rom_description(Video::VideoBase::CharacterROM::II));
-					rom_descriptions.emplace_back(machine_name, "the original Apple II ROM", "apple2o.rom", 12*1024, 0xba210588);
+					character = ROM::Name::AppleIICharacter;
+					system = ROM::Name::AppleIIOriginal;
 				break;
 				case Target::Model::IIplus:
-					rom_descriptions.push_back(video_.rom_description(Video::VideoBase::CharacterROM::II));
-					rom_descriptions.emplace_back(machine_name, "the Apple II+ ROM", "apple2.rom", 12*1024, 0xf66f9c26);
+					character = ROM::Name::AppleIICharacter;
+					system = ROM::Name::AppleIIPlus;
 				break;
 				case Target::Model::IIe:
-					rom_size += 3840;
-					rom_descriptions.push_back(video_.rom_description(Video::VideoBase::CharacterROM::IIe));
-					rom_descriptions.emplace_back(machine_name, "the Apple IIe ROM", "apple2eu.rom", 32*1024, 0xe12be18d);
+					character = ROM::Name::AppleIIeCharacter;
+					system = ROM::Name::AppleIIe;
 				break;
 				case Target::Model::EnhancedIIe:
-					rom_size += 3840;
-					rom_descriptions.push_back(video_.rom_description(Video::VideoBase::CharacterROM::EnhancedIIe));
-					rom_descriptions.emplace_back(machine_name, "the Enhanced Apple IIe ROM", "apple2e.rom", 32*1024, 0x65989942);
+					character = ROM::Name::AppleIIEnhancedECharacter;
+					system = ROM::Name::AppleIIEnhancedE;
 				break;
 			}
-			const auto roms = rom_fetcher(rom_descriptions);

-			// Try to install a Disk II card now, before checking the ROM list,
-			// to make sure that Disk II dependencies have been communicated.
-			if(target.disk_controller != Target::DiskController::None) {
+			ROM::Request request = ROM::Request(character) && ROM::Request(system);
+
+			// Add the necessary Disk II requests if appropriate.
+			const bool has_disk_controller = target.disk_controller != Target::DiskController::None;
+			const bool is_sixteen_sector = target.disk_controller == Target::DiskController::SixteenSector;
+			if(has_disk_controller) {
 				// Apple recommended slot 6 for the (first) Disk II.
-				install_card(6, new Apple::II::DiskIICard(rom_fetcher, target.disk_controller == Target::DiskController::SixteenSector));
+				request = request && DiskIICard::rom_request(is_sixteen_sector);
 			}

-			// Now, check and move the ROMs.
-			if(!roms[0] || !roms[1]) {
+			// Request, validate and install ROMs.
+			auto roms = rom_fetcher(request);
+			if(!request.validate(roms)) {
 				throw ROMMachine::Error::MissingROMs;
 			}

-			rom_ = std::move(*roms[1]);
-			if(rom_.size() > rom_size) {
-				rom_.erase(rom_.begin(), rom_.end() - off_t(rom_size));
+			if(has_disk_controller) {
+				install_card(6, new Apple::II::DiskIICard(roms, is_sixteen_sector));
 			}

-			video_.set_character_rom(*roms[0]);
+			rom_ = std::move(roms.find(system)->second);
+			// The IIe and Enhanced IIe ROMs often distributed are oversized; trim if necessary.
+			if(system == ROM::Name::AppleIIe || system == ROM::Name::AppleIIEnhancedE) {
+				if(rom_.size() > 16128) {
+					rom_.erase(rom_.begin(), rom_.end() - off_t(16128));
+				}
+			}
+			video_.set_character_rom(roms.find(character)->second);

 			// Set up the default memory blocks. On a II or II+ these values will never change.
 			// On a IIe they'll be affected by selection of auxiliary RAM.
@ -781,12 +787,14 @@ template <Analyser::Static::AppleII::Target::Model model> class ConcreteMachine:
 		std::unique_ptr<Reflection::Struct> get_options() final {
 			auto options = std::make_unique<Options>(Configurable::OptionsType::UserFriendly);
 			options->output = get_video_signal_configurable();
+			options->use_square_pixels = video_.get_use_square_pixels();
 			return options;
 		}

 		void set_options(const std::unique_ptr<Reflection::Struct> &str) {
 			const auto options = dynamic_cast<Options *>(str.get());
 			set_video_signal_configurable(options->output);
+			video_.set_use_square_pixels(options->use_square_pixels);
 		}

 		// MARK: MediaTarget
--- a/Machines/Apple/AppleII/AppleII.hpp
+++ b/Machines/Apple/AppleII/AppleII.hpp
@ -30,8 +30,11 @@ class Machine {
 		class Options: public Reflection::StructImpl<Options>, public Configurable::DisplayOption<Options> {
 			friend Configurable::DisplayOption<Options>;
 			public:
-				Options(Configurable::OptionsType) : Configurable::DisplayOption<Options>(Configurable::Display::CompositeColour)  {
+				bool use_square_pixels = false;
+
+				Options(Configurable::OptionsType) : Configurable::DisplayOption<Options>(Configurable::Display::CompositeColour) {
 					if(needs_declare()) {
+						DeclareField(use_square_pixels);
 						declare_display_option();
 						limit_enum(&output, Configurable::Display::CompositeMonochrome, Configurable::Display::CompositeColour, -1);
 					}
--- a/Machines/Apple/AppleII/DiskIICard.cpp
+++ b/Machines/Apple/AppleII/DiskIICard.cpp
@ -10,27 +10,34 @@

 using namespace Apple::II;

-DiskIICard::DiskIICard(const ROMMachine::ROMFetcher &rom_fetcher, bool is_16_sector) : diskii_(2045454) {
-	std::vector<std::unique_ptr<std::vector<uint8_t>>> roms;
+ROM::Request DiskIICard::rom_request(bool is_16_sector) {
 	if(is_16_sector) {
-		roms = rom_fetcher({
-			{"DiskII", "the Disk II 16-sector boot ROM", "boot-16.rom", 256, 0xce7144f6},
-			{"DiskII", "the Disk II 16-sector state machine ROM", "state-machine-16.rom", 256, { 0x9796a238, 0xb72a2c70 } }
-		});
+		return ROM::Request(ROM::Name::DiskIIBoot16Sector) && ROM::Request(ROM::Name::DiskIIStateMachine16Sector);
 	} else {
-		roms = rom_fetcher({
-			{"DiskII", "the Disk II 13-sector boot ROM", "boot-13.rom", 256, 0xd34eb2ff},
-			{"DiskII", "the Disk II 16-sector state machine ROM", "state-machine-16.rom", 256, { 0x9796a238, 0xb72a2c70 } }
-//			{"DiskII", "the Disk II 13-sector state machine ROM", "state-machine-13.rom", 256, 0x62e22620 }
-			/* TODO: once the DiskII knows how to decode common images of the 13-sector state machine, use that instead of the 16-sector. */
-		});
+		/* TODO: once the DiskII knows how to decode common images of the 13-sector state machine, use that instead of the 16-sector. */
+		return ROM::Request(ROM::Name::DiskIIBoot13Sector) && ROM::Request(ROM::Name::DiskIIStateMachine16Sector);
 	}
-	if(!roms[0] || !roms[1]) {
+}
+
+
+DiskIICard::DiskIICard(ROM::Map &map, bool is_16_sector) : diskii_(2045454) {
+	std::vector<std::unique_ptr<std::vector<uint8_t>>> roms;
+	ROM::Map::iterator state_machine, boot;
+	if(is_16_sector) {
+		state_machine = map.find(ROM::Name::DiskIIStateMachine16Sector);
+		boot = map.find(ROM::Name::DiskIIBoot16Sector);
+	} else {
+		// TODO: see above re: 13-sector state machine.
+		state_machine = map.find(ROM::Name::DiskIIStateMachine16Sector);
+		boot = map.find(ROM::Name::DiskIIBoot13Sector);
+	}
+
+	if(state_machine == map.end() || boot == map.end()) {
 		throw ROMMachine::Error::MissingROMs;
 	}

-	boot_ = std::move(*roms[0]);
-	diskii_.set_state_machine(*roms[1]);
+	boot_ = std::move(boot->second);
+	diskii_.set_state_machine(state_machine->second);
 	set_select_constraints(None);
 	diskii_.set_clocking_hint_observer(this);
 }
--- a/Machines/Apple/AppleII/DiskIICard.hpp
+++ b/Machines/Apple/AppleII/DiskIICard.hpp
@ -25,7 +25,8 @@ namespace II {

 class DiskIICard: public Card, public ClockingHint::Observer {
 	public:
-		DiskIICard(const ROMMachine::ROMFetcher &rom_fetcher, bool is_16_sector);
+		static ROM::Request rom_request(bool is_16_sector);
+		DiskIICard(ROM::Map &, bool is_16_sector);

 		void perform_bus_operation(Select select, bool is_read, uint16_t address, uint8_t *value) final;
 		void run_for(Cycles cycles, int stretches) final;
--- a/Machines/Apple/AppleII/Video.cpp
+++ b/Machines/Apple/AppleII/Video.cpp
@ -15,9 +15,8 @@ VideoBase::VideoBase(bool is_iie, std::function<void(Cycles)> &&target) :
 	crt_(910, 1, Outputs::Display::Type::NTSC60, Outputs::Display::InputDataType::Luminance1),
 	is_iie_(is_iie) {

-	// Show only the centre 75% of the TV frame.
 	crt_.set_display_type(Outputs::Display::DisplayType::CompositeColour);
-	crt_.set_visible_area(Outputs::Display::Rect(0.118f, 0.122f, 0.77f, 0.77f));
+	set_use_square_pixels(use_square_pixels_);

 	// TODO: there seems to be some sort of bug whereby switching modes can cause
 	// a signal discontinuity that knocks phase out of whack. So it isn't safe to
@ -26,6 +25,41 @@ VideoBase::VideoBase(bool is_iie, std::function<void(Cycles)> &&target) :
 //	crt_.set_immediate_default_phase(0.5f);
 }

+void VideoBase::set_use_square_pixels(bool use_square_pixels) {
+	use_square_pixels_ = use_square_pixels;
+
+	// HYPER-UGLY HACK. See correlated hack in the Macintosh.
+#ifdef __APPLE__
+	crt_.set_visible_area(Outputs::Display::Rect(0.128f, 0.122f, 0.75f, 0.77f));
+#else
+	if(use_square_pixels) {
+		crt_.set_visible_area(Outputs::Display::Rect(0.128f, 0.112f, 0.75f, 0.73f));
+	} else {
+		crt_.set_visible_area(Outputs::Display::Rect(0.128f, 0.12f, 0.75f, 0.77f));
+	}
+#endif
+
+	if(use_square_pixels) {
+		// From what I can make out, many contemporary Apple II monitors were
+		// calibrated slightly to stretch the Apple II's display slightly wider
+		// than it should be per the NTSC standards, for approximately square
+		// pixels. This reproduces that.
+
+		// 243 lines and 52µs are visible.
+		// i.e. to be square, 1 pixel should be: (1/243 * 52) * (3/4) = 156/972 = 39/243 µs
+		// On an Apple II each pixel is actually 1/7µs.
+		// Therefore the adjusted aspect ratio should be (4/3) * (39/243)/(1/7) = (4/3) * 273/243 = 1092/729 = 343/243 ~= 1.412
+		crt_.set_aspect_ratio(343.0f / 243.0f);
+	} else {
+		// Standard NTSC aspect ratio.
+		crt_.set_aspect_ratio(4.0f / 3.0f);
+	}
+}
+bool VideoBase::get_use_square_pixels() {
+	return use_square_pixels_;
+}
+
+
 void VideoBase::set_scan_target(Outputs::Display::ScanTarget *scan_target) {
 	crt_.set_scan_target(scan_target);
 }
--- a/Machines/Apple/AppleII/Video.hpp
+++ b/Machines/Apple/AppleII/Video.hpp
@ -51,8 +51,14 @@ class VideoBase: public VideoSwitches<Cycles> {
 		/// Gets the type of output.
 		Outputs::Display::DisplayType get_display_type() const;

+		/// Sets whether the current CRT should be recalibrated away from normative NTSC
+		/// to produce square pixels in 40-column text mode.
+		void set_use_square_pixels(bool);
+		bool get_use_square_pixels();
+
 	protected:
 		Outputs::CRT::CRT crt_;
+		bool use_square_pixels_ = false;

 		// State affecting output video stream generation.
 		uint8_t *pixel_pointer_ = nullptr;
--- a/Machines/Apple/AppleII/VideoSwitches.hpp
+++ b/Machines/Apple/AppleII/VideoSwitches.hpp
@ -228,36 +228,6 @@ template <typename TimeUnit> class VideoSwitches {
 			return external_.annunciator_3;
 		}

-		enum class CharacterROM {
-			/// The ROM that shipped with both the Apple II and the II+.
-			II,
-			/// The ROM that shipped with the original IIe.
-			IIe,
-			/// The ROM that shipped with the Enhanced IIe.
-			EnhancedIIe,
-			/// The ROM that shipped with the IIgs.
-			IIgs
-		};
-
-		/// @returns A file-level description of @c rom.
-		static ROMMachine::ROM rom_description(CharacterROM rom) {
-			const std::string machine_name = "AppleII";
-			switch(rom) {
-				case CharacterROM::II:
-					return ROMMachine::ROM(machine_name, "the basic Apple II character ROM", "apple2-character.rom", 2*1024, 0x64f415c6);
-
-				case CharacterROM::IIe:
-					return ROMMachine::ROM(machine_name, "the Apple IIe character ROM", "apple2eu-character.rom", 4*1024, 0x816a86f1);
-
-				default:	// To appease GCC.
-				case CharacterROM::EnhancedIIe:
-					return ROMMachine::ROM(machine_name, "the Enhanced Apple IIe character ROM", "apple2e-character.rom", 4*1024, 0x2651014d);
-
-				case CharacterROM::IIgs:
-					return ROMMachine::ROM(machine_name, "the Apple IIgs character ROM", "apple2gs.chr", 4*1024, 0x91e53cd8);
-			}
-		}
-
 		/// Set the character ROM for this video output.
 		void set_character_rom(const std::vector<uint8_t> &rom) {
 			character_rom_ = rom;
--- a/Machines/Apple/AppleIIgs/AppleIIgs.cpp
+++ b/Machines/Apple/AppleIIgs/AppleIIgs.cpp
@ -189,31 +189,23 @@ class ConcreteMachine:
 			speaker_.set_input_rate(float(CLOCK_RATE) / float(audio_divider));

 			using Target = Analyser::Static::AppleIIgs::Target;
-			std::vector<ROMMachine::ROM> rom_descriptions;
-			const std::string machine_name = "AppleIIgs";
+			ROM::Name system;
 			switch(target.model) {
-				case Target::Model::ROM00:
-					/* TODO */
-				case Target::Model::ROM01:
-					rom_descriptions.emplace_back(machine_name, "the Apple IIgs ROM01", "apple2gs.rom", 128*1024, 0x42f124b0);
-				break;
-
-				case Target::Model::ROM03:
-					rom_descriptions.emplace_back(machine_name, "the Apple IIgs ROM03", "apple2gs.rom2", 256*1024, 0xde7ddf29);
-				break;
+				case Target::Model::ROM00:	system = ROM::Name::AppleIIgsROM00;	break;
+				case Target::Model::ROM01:	system = ROM::Name::AppleIIgsROM01;	break;
+				default:					system = ROM::Name::AppleIIgsROM03;	break;
 			}
-			rom_descriptions.push_back(video_->rom_description(Video::Video::CharacterROM::EnhancedIIe));
+			constexpr ROM::Name characters = ROM::Name::AppleIIEnhancedECharacter;
+			constexpr ROM::Name microcontroller = ROM::Name::AppleIIgsMicrocontrollerROM03;

-			// TODO: pick a different ADB ROM for earlier machine revisions?
-			rom_descriptions.emplace_back(machine_name, "the Apple IIgs ADB microcontroller ROM", "341s0632-2", 4*1024, 0xe1c11fb0);
-
-			const auto roms = rom_fetcher(rom_descriptions);
-			if(!roms[0] || !roms[1] || !roms[2]) {
+			ROM::Request request = ROM::Request(system) && ROM::Request(characters) && ROM::Request(microcontroller);
+			auto roms = rom_fetcher(request);
+			if(!request.validate(roms)) {
 				throw ROMMachine::Error::MissingROMs;
 			}
-			rom_ = *roms[0];
-			video_->set_character_rom(*roms[1]);
-			adb_glu_->set_microcontroller_rom(*roms[2]);
+			rom_ = roms.find(system)->second;
+			video_->set_character_rom(roms.find(characters)->second);
+			adb_glu_->set_microcontroller_rom(roms.find(microcontroller)->second);

 			// Run only the currently-interesting self test.
 //			rom_[0x36402] = 2;
--- a/Machines/Apple/Macintosh/Macintosh.cpp
+++ b/Machines/Apple/Macintosh/Macintosh.cpp
@ -96,25 +96,24 @@ template <Analyser::Static::Macintosh::Target::Model model> class ConcreteMachin
 			using Model = Analyser::Static::Macintosh::Target::Model;
 			const std::string machine_name = "Macintosh";
 			uint32_t ram_size, rom_size;
-			std::vector<ROMMachine::ROM> rom_descriptions;
+			ROM::Name rom_name;
 			switch(model) {
 				default:
 				case Model::Mac128k:
 					ram_size = 128*1024;
 					rom_size = 64*1024;
-					rom_descriptions.emplace_back(machine_name, "the Macintosh 128k ROM", "mac128k.rom", 64*1024, 0x6d0c8a28);
+					rom_name = ROM::Name::Macintosh128k;
 				break;
 				case Model::Mac512k:
 					ram_size = 512*1024;
 					rom_size = 64*1024;
-					rom_descriptions.emplace_back(machine_name, "the Macintosh 512k ROM", "mac512k.rom", 64*1024, 0xcf759e0d);
+					rom_name = ROM::Name::Macintosh512k;
 				break;
 				case Model::Mac512ke:
 				case Model::MacPlus: {
 					ram_size = ((model == Model::MacPlus) ? 4096 : 512)*1024;
 					rom_size = 128*1024;
-					const std::initializer_list<uint32_t> crc32s = { 0x4fa5b399, 0x7cacd18f, 0xb2102e8e };
-					rom_descriptions.emplace_back(machine_name, "the Macintosh Plus ROM", "macplus.rom", 128*1024, crc32s);
+					rom_name = ROM::Name::MacintoshPlus;
 				} break;
 			}
 			ram_mask_ = ram_size - 1;
@ -123,12 +122,12 @@ template <Analyser::Static::Macintosh::Target::Model model> class ConcreteMachin
 			video_.set_ram(reinterpret_cast<uint16_t *>(ram_.data()), ram_mask_ >> 1);

 			// Grab a copy of the ROM and convert it into big-endian data.
-			const auto roms = rom_fetcher(rom_descriptions);
-			if(!roms[0]) {
+			ROM::Request request(rom_name);
+			auto roms = rom_fetcher(request);
+			if(!request.validate(roms)) {
 				throw ROMMachine::Error::MissingROMs;
 			}
-			roms[0]->resize(rom_size);
-			Memory::PackBigEndian16(*roms[0], rom_);
+			Memory::PackBigEndian16(roms.find(rom_name)->second, rom_);

 			// Randomise memory contents.
 			Memory::Fuzz(ram_);
--- a/Machines/Atari/ST/AtariST.cpp
+++ b/Machines/Atari/ST/AtariST.cpp
@ -74,15 +74,13 @@ class ConcreteMachine:
 			video_->set_ram(reinterpret_cast<uint16_t *>(ram_.data()), ram_.size());
 			Memory::Fuzz(ram_);

-			std::vector<ROMMachine::ROM> rom_descriptions = {
-				{"AtariST", "the UK TOS 1.00 ROM", "tos100.img", 192*1024, 0x1a586c64}
-//				{"AtariST", "the UK TOS 1.04 ROM", "tos104.img", 192*1024, 0xa50d1d43}
-			};
-			const auto roms = rom_fetcher(rom_descriptions);
-			if(!roms[0]) {
+			constexpr ROM::Name rom_name = ROM::Name::AtariSTTOS100;
+			ROM::Request request(rom_name);
+			auto roms = rom_fetcher(request);
+			if(!request.validate(roms)) {
 				throw ROMMachine::Error::MissingROMs;
 			}
-			Memory::PackBigEndian16(*roms[0], rom_);
+			Memory::PackBigEndian16(roms.find(rom_name)->second, rom_);

 			// Set up basic memory map.
 			memory_map_[0] = BusDevice::MostlyRAM;
--- a/Machines/ColecoVision/ColecoVision.cpp
+++ b/Machines/ColecoVision/ColecoVision.cpp
@ -127,15 +127,13 @@ class ConcreteMachine:
 			joysticks_.emplace_back(new Joystick);
 			joysticks_.emplace_back(new Joystick);

-			const auto roms = rom_fetcher(
-				{ {"ColecoVision", "the ColecoVision BIOS", "coleco.rom", 8*1024, 0x3aa93ef3} });
-
-			if(!roms[0]) {
+			constexpr ROM::Name rom_name = ROM::Name::ColecoVisionBIOS;
+			const ROM::Request request(rom_name);
+			auto roms = rom_fetcher(request);
+			if(!request.validate(roms)) {
 				throw ROMMachine::Error::MissingROMs;
 			}
-
-			bios_ = *roms[0];
-			bios_.resize(8192);
+			bios_ = roms.find(rom_name)->second;

 			if(!target.media.cartridges.empty()) {
 				const auto &segment = target.media.cartridges.front()->get_segments().front();
--- a/Machines/Commodore/1540/C1540.hpp
+++ b/Machines/Commodore/1540/C1540.hpp
@ -41,7 +41,8 @@ namespace C1540 {
 */
 class Machine final: public MachineBase {
 	public:
-		Machine(Personality personality, const ROMMachine::ROMFetcher &rom_fetcher);
+		static ROM::Request rom_request(Personality personality);
+		Machine(Personality personality, const ROM::Map &roms);

 		/*!
 			Sets the serial bus to which this drive should attach itself.
--- a/Machines/Commodore/1540/Implementation/C1540.cpp
+++ b/Machines/Commodore/1540/Implementation/C1540.cpp
@ -16,7 +16,15 @@

 using namespace Commodore::C1540;

-MachineBase::MachineBase(Personality personality, const ROMMachine::ROMFetcher &rom_fetcher) :
+ROM::Request Machine::rom_request(Personality personality) {
+	switch(personality) {
+		default:
+		case Personality::C1540:	return ROM::Request(ROM::Name::Commodore1540);
+		case Personality::C1541:	return ROM::Request(ROM::Name::Commodore1541);
+	}
+}
+
+MachineBase::MachineBase(Personality personality, const ROM::Map &roms) :
 		Storage::Disk::Controller(1000000),
 		m6502_(*this),
 		serial_port_VIA_port_handler_(new SerialPortVIA(serial_port_VIA_)),
@ -39,28 +47,22 @@ MachineBase::MachineBase(Personality personality, const ROMMachine::ROMFetcher &
 	emplace_drive(1000000, 300, 2);
 	set_drive(1);

-	std::string device_name;
-	uint32_t crc = 0;
+	ROM::Name rom_name;
 	switch(personality) {
-		case Personality::C1540:
-			device_name = "1540";
-			crc = 0x718d42b1;
-		break;
-		case Personality::C1541:
-			device_name = "1541";
-			crc = 0xfb760019;
-		break;
+		default:
+		case Personality::C1540:	rom_name = ROM::Name::Commodore1540;	break;
+		case Personality::C1541:	rom_name = ROM::Name::Commodore1541;	break;
 	}

-	auto roms = rom_fetcher({ {"Commodore1540", "the " + device_name + " ROM", device_name + ".bin", 16*1024, crc} });
-	if(!roms[0]) {
+	auto rom = roms.find(rom_name);
+	if(rom == roms.end()) {
 		throw ROMMachine::Error::MissingROMs;
 	}
-	std::memcpy(rom_, roms[0]->data(), std::min(sizeof(rom_), roms[0]->size()));
+	std::memcpy(rom_, roms.find(rom_name)->second.data(), std::min(sizeof(rom_), roms.find(rom_name)->second.size()));
 }

-Machine::Machine(Personality personality, const ROMMachine::ROMFetcher &rom_fetcher) :
-	MachineBase(personality, rom_fetcher) {}
+Machine::Machine(Personality personality, const ROM::Map &roms) :
+	MachineBase(personality, roms) {}

 void Machine::set_serial_bus(std::shared_ptr<::Commodore::Serial::Bus> serial_bus) {
 	Commodore::Serial::AttachPortAndBus(serial_port_, serial_bus);
--- a/Machines/Commodore/1540/Implementation/C1540Base.hpp
+++ b/Machines/Commodore/1540/Implementation/C1540Base.hpp
@ -127,7 +127,7 @@ class MachineBase:
 	public Storage::Disk::Controller {

 	public:
-		MachineBase(Personality personality, const ROMMachine::ROMFetcher &rom_fetcher);
+		MachineBase(Personality personality, const ROM::Map &roms);

 		// to satisfy CPU::MOS6502::Processor
 		Cycles perform_bus_operation(CPU::MOS6502::BusOperation operation, uint16_t address, uint8_t *value);
--- a/Machines/Commodore/Vic-20/Vic20.cpp
+++ b/Machines/Commodore/Vic-20/Vic20.cpp
@ -316,53 +316,48 @@ class ConcreteMachine:
 			// Install a joystick.
 			joysticks_.emplace_back(new Joystick(*user_port_via_port_handler_, *keyboard_via_port_handler_));

-			const std::string machine_name = "Vic20";
-			std::vector<ROMMachine::ROM> rom_names = {
-				{machine_name, "the VIC-20 BASIC ROM", "basic.bin", 8*1024, 0xdb4c43c1}
-			};
+			ROM::Request request(ROM::Name::Vic20BASIC);
+			ROM::Name kernel, character;
 			switch(target.region) {
 				default:
-					rom_names.emplace_back(machine_name, "the English-language VIC-20 character ROM", "characters-english.bin", 4*1024, 0x83e032a6);
-					rom_names.emplace_back(machine_name, "the English-language PAL VIC-20 kernel ROM", "kernel-pal.bin", 8*1024, 0x4be07cb4);
+					character = ROM::Name::Vic20EnglishCharacters;
+					kernel = ROM::Name::Vic20EnglishPALKernel;
 				break;
 				case Analyser::Static::Commodore::Target::Region::American:
-					rom_names.emplace_back(machine_name, "the English-language VIC-20 character ROM", "characters-english.bin", 4*1024, 0x83e032a6);
-					rom_names.emplace_back(machine_name, "the English-language NTSC VIC-20 kernel ROM", "kernel-ntsc.bin", 8*1024, 0xe5e7c174);
+					character = ROM::Name::Vic20EnglishCharacters;
+					kernel = ROM::Name::Vic20EnglishNTSCKernel;
 				break;
 				case Analyser::Static::Commodore::Target::Region::Danish:
-					rom_names.emplace_back(machine_name, "the Danish VIC-20 character ROM", "characters-danish.bin", 4*1024, 0x7fc11454);
-					rom_names.emplace_back(machine_name, "the Danish VIC-20 kernel ROM", "kernel-danish.bin", 8*1024, 0x02adaf16);
+					character = ROM::Name::Vic20DanishCharacters;
+					kernel = ROM::Name::Vic20DanishKernel;
 				break;
 				case Analyser::Static::Commodore::Target::Region::Japanese:
-					rom_names.emplace_back(machine_name, "the Japanese VIC-20 character ROM", "characters-japanese.bin", 4*1024, 0xfcfd8a4b);
-					rom_names.emplace_back(machine_name, "the Japanese VIC-20 kernel ROM", "kernel-japanese.bin", 8*1024, 0x336900d7);
+					character = ROM::Name::Vic20JapaneseCharacters;
+					kernel = ROM::Name::Vic20JapaneseKernel;
 				break;
 				case Analyser::Static::Commodore::Target::Region::Swedish:
-					rom_names.emplace_back(machine_name, "the Swedish VIC-20 character ROM", "characters-swedish.bin", 4*1024, 0xd808551d);
-					rom_names.emplace_back(machine_name, "the Swedish VIC-20 kernel ROM", "kernel-swedish.bin", 8*1024, 0xb2a60662);
+					character = ROM::Name::Vic20SwedishCharacters;
+					kernel = ROM::Name::Vic20SwedishKernel;
 				break;
 			}

-			const auto roms = rom_fetcher(rom_names);
+			if(target.has_c1540) {
+				request = request && Commodore::C1540::Machine::rom_request(Commodore::C1540::Personality::C1540);
+			}
+			request = request && ROM::Request(character) && ROM::Request(kernel);

-			for(const auto &rom: roms) {
-				if(!rom) {
-					throw ROMMachine::Error::MissingROMs;
-				}
+			auto roms = rom_fetcher(request);
+			if(!request.validate(roms)) {
+				throw ROMMachine::Error::MissingROMs;
 			}

-			basic_rom_ = std::move(*roms[0]);
-			character_rom_ = std::move(*roms[1]);
-			kernel_rom_ = std::move(*roms[2]);
-
-			// Characters ROMs should be 4kb.
-			character_rom_.resize(4096);
-			// Kernel ROMs and the BASIC ROM should be 8kb.
-			kernel_rom_.resize(8192);
+			basic_rom_ = std::move(roms.find(ROM::Name::Vic20BASIC)->second);
+			character_rom_ = std::move(roms.find(character)->second);
+			kernel_rom_ = std::move(roms.find(kernel)->second);

 			if(target.has_c1540) {
 				// construct the 1540
-				c1540_ = std::make_unique<::Commodore::C1540::Machine>(Commodore::C1540::Personality::C1540, rom_fetcher);
+				c1540_ = std::make_unique<::Commodore::C1540::Machine>(Commodore::C1540::Personality::C1540, roms);

 				// attach it to the serial bus
 				c1540_->set_serial_bus(serial_bus_);
--- a/Machines/Electron/Electron.cpp
+++ b/Machines/Electron/Electron.cpp
@ -69,37 +69,25 @@ template <bool has_scsi_bus> class ConcreteMachine:
 			speaker_.set_input_rate(2000000 / SoundGenerator::clock_rate_divider);
 			speaker_.set_high_frequency_cutoff(6000);

-			const std::string machine_name = "Electron";
-			std::vector<ROMMachine::ROM> required_roms = {
-				{machine_name, "the Acorn BASIC II ROM", "basic.rom", 16*1024, 0x79434781},
-				{machine_name, "the Electron MOS ROM", "os.rom", 16*1024, 0xbf63fb1f}
-			};
-			const size_t pres_adfs_rom_position = required_roms.size();
+			::ROM::Request request = ::ROM::Request(::ROM::Name::AcornBASICII) && ::ROM::Request(::ROM::Name::AcornElectronMOS100);
 			if(target.has_pres_adfs) {
-				required_roms.emplace_back(machine_name, "the E00 ADFS ROM, first slot", "ADFS-E00_1.rom", 16*1024, 0x51523993);
-				required_roms.emplace_back(machine_name, "the E00 ADFS ROM, second slot", "ADFS-E00_2.rom", 16*1024, 0x8d17de0e);
+				request = request && ::ROM::Request(::ROM::Name::PRESADFSSlot1) && ::ROM::Request(::ROM::Name::PRESADFSSlot2);
 			}
-			const size_t acorn_adfs_rom_position = required_roms.size();
 			if(target.has_acorn_adfs) {
-				required_roms.emplace_back(machine_name, "the Acorn ADFS ROM", "adfs.rom", 16*1024, 0x3289bdc6);
+				request = request && ::ROM::Request(::ROM::Name::AcornADFS);
 			}
-			const size_t dfs_rom_position = required_roms.size();
 			if(target.has_dfs) {
-				required_roms.emplace_back(machine_name, "the 1770 DFS ROM", "DFS-1770-2.20.rom", 16*1024, 0xf3dc9bc5);
+				request = request && ::ROM::Request(::ROM::Name::Acorn1770DFS);
 			}
-			const size_t ap6_rom_position = required_roms.size();
 			if(target.has_ap6_rom) {
-				required_roms.emplace_back(machine_name, "the 8kb Advanced Plus 6 ROM", "AP6v133.rom", 8*1024, 0xe0013cfc);
+				request = request && ::ROM::Request(::ROM::Name::PRESAdvancedPlus6);
 			}
-			const auto roms = rom_fetcher(required_roms);
-
-			for(const auto &rom: roms) {
-				if(!rom) {
-					throw ROMMachine::Error::MissingROMs;
-				}
+			auto roms = rom_fetcher(request);
+			if(!request.validate(roms)) {
+				throw ROMMachine::Error::MissingROMs;
 			}
-			set_rom(ROM::BASIC, *roms[0], false);
-			set_rom(ROM::OS, *roms[1], false);
+			set_rom(ROM::BASIC, roms.find(::ROM::Name::AcornBASICII)->second, false);
+			set_rom(ROM::OS, roms.find(::ROM::Name::AcornElectronMOS100)->second, false);

 			/*
 				ROM slot mapping applied:
@ -115,19 +103,18 @@ template <bool has_scsi_bus> class ConcreteMachine:
 				plus3_ = std::make_unique<Plus3>();

 				if(target.has_dfs) {
-					set_rom(ROM::Slot0, *roms[dfs_rom_position], true);
+					set_rom(ROM::Slot0, roms.find(::ROM::Name::Acorn1770DFS)->second, true);
 				}
 				if(target.has_pres_adfs) {
-					set_rom(ROM::Slot4, *roms[pres_adfs_rom_position], true);
-					set_rom(ROM::Slot5, *roms[pres_adfs_rom_position+1], true);
+					set_rom(ROM::Slot4, roms.find(::ROM::Name::PRESADFSSlot1)->second, true);
+					set_rom(ROM::Slot5, roms.find(::ROM::Name::PRESADFSSlot2)->second, true);
 				}
 				if(target.has_acorn_adfs) {
-					set_rom(ROM::Slot6, *roms[acorn_adfs_rom_position], true);
+					set_rom(ROM::Slot6, roms.find(::ROM::Name::AcornADFS)->second, true);
 				}
 			}
-
 			if(target.has_ap6_rom) {
-				set_rom(ROM::Slot15, *roms[ap6_rom_position], true);
+				set_rom(ROM::Slot15, roms.find(::ROM::Name::PRESAdvancedPlus6)->second, true);
 			}

 			if(target.has_sideways_ram) {
--- a/Machines/MSX/MSX.cpp
+++ b/Machines/MSX/MSX.cpp
@ -169,19 +169,22 @@ class ConcreteMachine:

 			// Install the proper TV standard and select an ideal BIOS name.
 			const std::string machine_name = "MSX";
-			std::vector<ROMMachine::ROM> required_roms = {
-				{machine_name, "any MSX BIOS", "msx.rom", 32*1024, 0x94ee12f3}
-			};
+			ROM::Request bios_request = ROM::Request(ROM::Name::MSXGenericBIOS);
+//			std::vector<ROMMachine::ROM> required_roms = {
+//				{machine_name, "any MSX BIOS", "msx.rom", 32*1024, 0x94ee12f3u}
+//			};

 			bool is_ntsc = true;
 			uint8_t character_generator = 1;	/* 0 = Japan, 1 = USA, etc, 2 = USSR */
 			uint8_t date_format = 1;			/* 0 = Y/M/D, 1 = M/D/Y, 2 = D/M/Y */
 			uint8_t keyboard = 1;				/* 0 = Japan, 1 = USA, 2 = France, 3 = UK, 4 = Germany, 5 = USSR, 6 = Spain */
+			ROM::Name regional_bios_name;

 			// TODO: CRCs below are incomplete, at best.
 			switch(target.region) {
+				default:
 				case Target::Region::Japan:
-					required_roms.emplace_back(machine_name, "a Japanese MSX BIOS", "msx-japanese.rom", 32*1024, 0xee229390);
+					regional_bios_name = ROM::Name::MSXJapaneseBIOS;
 					vdp_->set_tv_standard(TI::TMS::TVStandard::NTSC);

 					is_ntsc = true;
@ -189,7 +192,7 @@ class ConcreteMachine:
 					date_format = 0;
 				break;
 				case Target::Region::USA:
-					required_roms.emplace_back(machine_name, "an American MSX BIOS", "msx-american.rom", 32*1024, 0);
+					regional_bios_name = ROM::Name::MSXAmericanBIOS;
 					vdp_->set_tv_standard(TI::TMS::TVStandard::NTSC);

 					is_ntsc = true;
@ -197,7 +200,7 @@ class ConcreteMachine:
 					date_format = 1;
 				break;
 				case Target::Region::Europe:
-					required_roms.emplace_back(machine_name, "a European MSX BIOS", "msx-european.rom", 32*1024, 0);
+					regional_bios_name = ROM::Name::MSXEuropeanBIOS;
 					vdp_->set_tv_standard(TI::TMS::TVStandard::PAL);

 					is_ntsc = false;
@ -205,27 +208,30 @@ class ConcreteMachine:
 					date_format = 2;
 				break;
 			}
+			bios_request = bios_request || ROM::Request(regional_bios_name);

 			// Fetch the necessary ROMs; try the region-specific ROM first,
 			// but failing that fall back on patching the main one.
-			size_t disk_index = 0;
+			ROM::Request request;
 			if(target.has_disk_drive) {
-				disk_index = required_roms.size();
-				required_roms.emplace_back(machine_name, "the MSX-DOS ROM", "disk.rom", 16*1024, 0x721f61df);
+				request = ROM::Request(ROM::Name::MSXDOS) && bios_request;
+			} else {
+				request = bios_request;
 			}
-			const auto roms = rom_fetcher(required_roms);

-			if((!roms[0] && !roms[1]) || (target.has_disk_drive && !roms[2])) {
+			auto roms = rom_fetcher(request);
+			if(!request.validate(roms)) {
 				throw ROMMachine::Error::MissingROMs;
 			}

 			// Figure out which BIOS to use, either a specific one or the generic
 			// one appropriately patched.
-			if(roms[1]) {
-				memory_slots_[0].source = std::move(*roms[1]);
+			const auto regional_bios = roms.find(regional_bios_name);
+			if(regional_bios != roms.end()) {
+				memory_slots_[0].source = std::move(regional_bios->second);
 				memory_slots_[0].source.resize(32768);
 			} else {
-				memory_slots_[0].source = std::move(*roms[0]);
+				memory_slots_[0].source = std::move(roms.find(ROM::Name::MSXGenericBIOS)->second);
 				memory_slots_[0].source.resize(32768);

 				memory_slots_[0].source[0x2b] = uint8_t(
@ -252,7 +258,7 @@ class ConcreteMachine:
 			// Add a disk cartridge if any disks were supplied.
 			if(target.has_disk_drive) {
 				memory_slots_[2].set_handler(new DiskROM(memory_slots_[2].source));
-				memory_slots_[2].source = std::move(*roms[disk_index]);
+				memory_slots_[2].source = std::move(roms.find(ROM::Name::MSXDOS)->second);
 				memory_slots_[2].source.resize(16384);

 				map(2, 0, 0x4000, 0x2000);
--- a/Machines/MasterSystem/MasterSystem.cpp
+++ b/Machines/MasterSystem/MasterSystem.cpp
@ -141,23 +141,20 @@ class ConcreteMachine:
 			//	0072ed54 = US/European BIOS 1.3
 			//	48d44a13 = Japanese BIOS 2.1
 			const bool is_japanese = target.region == Target::Region::Japan;
-			const auto roms = rom_fetcher(
-				{ {"MasterSystem",
-					is_japanese ? "the Japanese Master System BIOS" : "the European/US Master System BIOS",
-					is_japanese ? "japanese-bios.sms" : "bios.sms",
-					8*1024,
-					{ is_japanese ? 0x48d44a13u : 0x0072ed54u }
-				} }
-			);
-			if(!roms[0]) {
+			const ROM::Name bios_name = is_japanese ? ROM::Name::MasterSystemJapaneseBIOS : ROM::Name::MasterSystemWesternBIOS;
+			ROM::Request request(bios_name, true);
+			auto roms = rom_fetcher(request);
+			request.validate(roms);
+
+			const auto rom = roms.find(bios_name);
+			if(rom == roms.end()) {
 				// No BIOS found; attempt to boot as though it has already disabled itself.
 				has_bios_ = false;
 				memory_control_ |= 0x08;
 				std::cerr << "No BIOS found; attempting to start cartridge directly" << std::endl;
 			} else {
 				has_bios_ = true;
-				roms[0]->resize(8*1024);
-				memcpy(&bios_, roms[0]->data(), roms[0]->size());
+				memcpy(&bios_, rom->second.data(), std::min(sizeof(bios_), rom->second.size()));
 			}
 			page_cartridge();

--- a/Machines/Oric/Oric.cpp
+++ b/Machines/Oric/Oric.cpp
@ -304,73 +304,64 @@ template <Analyser::Static::Oric::Target::DiskInterface disk_interface, CPU::MOS
 				ram_[c] |= 0x40;
 			}

-			const std::string machine_name = "Oric";
-			std::vector<ROMMachine::ROM> rom_names = { {machine_name, "the Oric colour ROM", "colour.rom", 128, 0xd50fca65} };
+			::ROM::Request request = ::ROM::Request(::ROM::Name::OricColourROM, true);
+			::ROM::Name basic;
 			switch(target.rom) {
-				case Analyser::Static::Oric::Target::ROM::BASIC10:
-					rom_names.emplace_back(machine_name, "Oric BASIC 1.0", "basic10.rom", 16*1024, 0xf18710b4);
-				break;
-				case Analyser::Static::Oric::Target::ROM::BASIC11:
-					rom_names.emplace_back(machine_name, "Oric BASIC 1.1", "basic11.rom", 16*1024, 0xc3a92bef);
-				break;
-				case Analyser::Static::Oric::Target::ROM::Pravetz:
-					rom_names.emplace_back(machine_name, "Pravetz BASIC", "pravetz.rom", 16*1024, 0x58079502);
-				break;
+				case Analyser::Static::Oric::Target::ROM::BASIC10:	basic = ::ROM::Name::OricBASIC10;		break;
+				default:
+				case Analyser::Static::Oric::Target::ROM::BASIC11:	basic = ::ROM::Name::OricBASIC11;		break;
+				case Analyser::Static::Oric::Target::ROM::Pravetz:	basic = ::ROM::Name::OricPravetzBASIC;	break;
 			}
-			size_t diskii_state_machine_index = 0;
+			request = request && ::ROM::Request(basic);
+
 			switch(disk_interface) {
 				default: break;
 				case DiskInterface::BD500:
-					rom_names.emplace_back(machine_name, "the Oric Byte Drive 500 ROM", "bd500.rom", 8*1024, 0x61952e34);
+					request = request && ::ROM::Request(::ROM::Name::OricByteDrive500);
 				break;
 				case DiskInterface::Jasmin:
-					rom_names.emplace_back(machine_name, "the Oric Jasmin ROM", "jasmin.rom", 2*1024, 0x37220e89);
+					request = request && ::ROM::Request(::ROM::Name::OricJasmin);
 				break;
 				case DiskInterface::Microdisc:
-					rom_names.emplace_back(machine_name, "the Oric Microdisc ROM", "microdisc.rom", 8*1024, 0xa9664a9c);
+					request = request && ::ROM::Request(::ROM::Name::OricMicrodisc);
 				break;
 				case DiskInterface::Pravetz:
-					rom_names.emplace_back(machine_name, "the 8DOS boot ROM", "8dos.rom", 512, 0x49a74c06);
-					// These ROM details are coupled with those in the DiskIICard.
-					diskii_state_machine_index = rom_names.size();
-					rom_names.push_back({"DiskII", "the Disk II 16-sector state machine ROM", "state-machine-16.rom", 256, { 0x9796a238, 0xb72a2c70 }});
+					request = request && ::ROM::Request(::ROM::Name::Oric8DOSBoot) && ::ROM::Request(::ROM::Name::DiskIIStateMachine16Sector);
 				break;
 			}

-			const auto roms = rom_fetcher(rom_names);
-
-			for(std::size_t index = 0; index < roms.size(); ++index) {
-				if(!roms[index]) {
-					throw ROMMachine::Error::MissingROMs;
-				}
+			auto roms = rom_fetcher(request);
+			if(!request.validate(roms)) {
+				throw ROMMachine::Error::MissingROMs;
 			}

-			video_->set_colour_rom(*roms[0]);
-			rom_ = std::move(*roms[1]);
+			// The colour ROM is optional; an alternative composite encoding can be used if
+			// it is absent.
+			const auto colour_rom = roms.find(::ROM::Name::OricColourROM);
+			if(colour_rom != roms.end()) {
+				video_->set_colour_rom(colour_rom->second);
+			}
+			rom_ = std::move(roms.find(basic)->second);

 			switch(disk_interface) {
 				default: break;
 				case DiskInterface::BD500:
-					disk_rom_ = std::move(*roms[2]);
-					disk_rom_.resize(8192);
+					disk_rom_ = std::move(roms.find(::ROM::Name::OricByteDrive500)->second);
 				break;
 				case DiskInterface::Jasmin:
-					disk_rom_ = std::move(*roms[2]);
-					disk_rom_.resize(2048);
+					disk_rom_ = std::move(roms.find(::ROM::Name::OricJasmin)->second);
 				break;
 				case DiskInterface::Microdisc:
-					disk_rom_ = std::move(*roms[2]);
-					disk_rom_.resize(8192);
+					disk_rom_ = std::move(roms.find(::ROM::Name::OricMicrodisc)->second);
 				break;
 				case DiskInterface::Pravetz: {
-					pravetz_rom_ = std::move(*roms[2]);
+					pravetz_rom_ = std::move(roms.find(::ROM::Name::Oric8DOSBoot)->second);
 					pravetz_rom_.resize(512);

-					diskii_->set_state_machine(*roms[diskii_state_machine_index]);
+					diskii_->set_state_machine(roms.find(::ROM::Name::DiskIIStateMachine16Sector)->second);
 				} break;
 			}

-			rom_.resize(16384);
 			paged_rom_ = rom_.data();

 			switch(target.disk_interface) {
--- a/Machines/Oric/Video.cpp
+++ b/Machines/Oric/Video.cpp
@ -54,7 +54,7 @@ void VideoOutput::set_display_type(Outputs::Display::DisplayType display_type) {

 #ifdef SUPPLY_COMPOSITE
 	const auto data_type =
-		(display_type == Outputs::Display::DisplayType::RGB) ?
+		(!has_colour_rom_ || display_type == Outputs::Display::DisplayType::RGB) ?
 			Outputs::Display::InputDataType::Red1Green1Blue1 :
 			Outputs::Display::InputDataType::PhaseLinkedLuminance8;
 #else
@ -80,6 +80,7 @@ Outputs::Display::ScanStatus VideoOutput::get_scaled_scan_status() const {
 }

 void VideoOutput::set_colour_rom(const std::vector<uint8_t> &rom) {
+	has_colour_rom_ = true;
 	for(std::size_t c = 0; c < 8; c++) {
 		colour_forms_[c] = 0;

--- a/Machines/Oric/Video.hpp
+++ b/Machines/Oric/Video.hpp
@ -37,6 +37,7 @@ class VideoOutput {
 		Outputs::CRT::CRT crt_;
 		Outputs::CRT::CRTFrequencyMismatchWarner<VideoOutput> frequency_mismatch_warner_;
 		bool crt_is_60Hz_ = false;
+		bool has_colour_rom_ = false;

 		void update_crt_frequency();

--- a/Machines/ROMMachine.hpp
+++ b/Machines/ROMMachine.hpp
@ -10,38 +10,16 @@
 #define ROMMachine_hpp

 #include <functional>
+#include <map>
 #include <memory>
+#include <optional>
 #include <string>
 #include <vector>

+#include "Utility/ROMCatalogue.hpp"
+
 namespace ROMMachine {

-/*!
-	Describes a ROM image; this term is used in this emulator strictly in the sense of firmware —
-	system software that is an inherent part of a machine.
-*/
-struct ROM {
-	/// The machine with which this ROM is associated, in a form that is safe for using as
-	/// part of a file name.
-	std::string machine_name;
-	/// A descriptive name for this ROM, suitable for use in a bullet-point list, a bracket
-	/// clause, etc, e.g. "the Electron MOS 1.0".
-	std::string descriptive_name;
-	/// An idiomatic file name for this ROM, e.g. "os10.rom".
-	std::string file_name;
-	/// The expected size of this ROM in bytes, e.g. 32768.
-	size_t size = 0;
-	/// CRC32s for all known acceptable copies of this ROM; intended to allow a host platform
-	/// to test user-provided ROMs of unknown provenance. **Not** intended to be used
-	/// to exclude ROMs where the user's intent is otherwise clear.
-	std::vector<uint32_t> crc32s;
-
-	ROM(std::string machine_name, std::string descriptive_name, std::string file_name, size_t size, uint32_t crc32) :
-		machine_name(machine_name), descriptive_name(descriptive_name), file_name(file_name), size(size), crc32s({crc32}) {}
-	ROM(std::string machine_name, std::string descriptive_name, std::string file_name, size_t size, std::initializer_list<uint32_t> crc32s) :
-		machine_name(machine_name), descriptive_name(descriptive_name), file_name(file_name), size(size), crc32s(crc32s) {}
-};
-
 /*!
 	Defines the signature for a function that must be supplied by the host environment in order to give machines
 	a route for fetching any system ROMs they might need.
@ -50,7 +28,7 @@ struct ROM {
 	return a vector of unique_ptrs that either contain the contents of the ROM from @c names that corresponds by
 	index, or else are @c nullptr.
 */
-typedef std::function<std::vector<std::unique_ptr<std::vector<uint8_t>>>(const std::vector<ROM> &roms)> ROMFetcher;
+typedef std::function<ROM::Map(const ROM::Request &request)> ROMFetcher;

 enum class Error {
 	MissingROMs
--- a/Machines/Sinclair/ZX8081/ZX8081.cpp
+++ b/Machines/Sinclair/ZX8081/ZX8081.cpp
@ -74,15 +74,13 @@ template<bool is_zx81> class ConcreteMachine:
 			speaker_.set_input_rate(float(ZX8081ClockRate) / 2.0f);

 			const bool use_zx81_rom = target.is_ZX81 || target.ZX80_uses_ZX81_ROM;
-			const auto roms =
-				use_zx81_rom ?
-					rom_fetcher({ {"ZX8081", "the ZX81 BASIC ROM", "zx81.rom", 8 * 1024, 0x4b1dd6eb} }) :
-					rom_fetcher({ {"ZX8081", "the ZX80 BASIC ROM", "zx80.rom", 4 * 1024, 0x4c7fc597} });
-
-			if(!roms[0]) throw ROMMachine::Error::MissingROMs;
-
-			rom_ = std::move(*roms[0]);
-			rom_.resize(use_zx81_rom ? 8192 : 4096);
+			const ROM::Name rom_name = use_zx81_rom ? ROM::Name::ZX81 : ROM::Name::ZX80;
+			const ROM::Request request(rom_name);
+			auto roms = rom_fetcher(request);
+			if(!request.validate(roms)) {
+				throw ROMMachine::Error::MissingROMs;
+			}
+			rom_ = std::move(roms.find(rom_name)->second);

 			rom_mask_ = uint16_t(rom_.size() - 1);

--- a/Machines/Sinclair/ZXSpectrum/ZXSpectrum.cpp
+++ b/Machines/Sinclair/ZXSpectrum/ZXSpectrum.cpp
@ -146,33 +146,24 @@ template<Model model> class ConcreteMachine:
 			set_clock_rate(clock_rate());
 			speaker_.set_input_rate(float(clock_rate()) / 2.0f);

-			// With only the +2a and +3 currently supported, the +3 ROM is always
-			// the one required.
-			std::vector<ROMMachine::ROM> rom_names;
-			const std::string machine = "ZXSpectrum";
+			ROM::Name rom_name;
 			switch(model) {
 				case Model::SixteenK:
-				case Model::FortyEightK:
-					rom_names.emplace_back(machine, "the 48kb ROM", "48.rom", 16 * 1024, 0xddee531f);
-				break;
-
-				case Model::OneTwoEightK:
-					rom_names.emplace_back(machine, "the 128kb ROM", "128.rom", 32 * 1024, 0x2cbe8995);
-				break;
-
-				case Model::Plus2:
-					rom_names.emplace_back(machine, "the +2 ROM", "plus2.rom", 32 * 1024, 0xe7a517dc);
-				break;
-
+				case Model::FortyEightK:	rom_name = ROM::Name::Spectrum48k;		break;
+				case Model::OneTwoEightK:	rom_name = ROM::Name::Spectrum128k;		break;
+				case Model::Plus2:			rom_name = ROM::Name::SpecrumPlus2;		break;
 				case Model::Plus2a:
-				case Model::Plus3: {
-					const std::initializer_list<uint32_t> crc32s = { 0x96e3c17a, 0xbe0d9ec4 };
-					rom_names.emplace_back(machine, "the +2a/+3 ROM", "plus3.rom", 64 * 1024, crc32s);
-				} break;
+				case Model::Plus3: 			rom_name = ROM::Name::SpectrumPlus3;	break;
+				// TODO: possibly accept the +3 ROM in multiple parts?
 			}
-			const auto roms = rom_fetcher(rom_names);
-			if(!roms[0]) throw ROMMachine::Error::MissingROMs;
-			memcpy(rom_.data(), roms[0]->data(), std::min(rom_.size(), roms[0]->size()));
+			const auto request = ROM::Request(rom_name);
+			auto roms = rom_fetcher(request);
+			if(!request.validate(roms)) {
+				throw ROMMachine::Error::MissingROMs;
+			}
+
+			const auto &rom = roms.find(rom_name)->second;
+			memcpy(rom_.data(), rom.data(), std::min(rom_.size(), rom.size()));

 			// Register for sleeping notifications.
 			tape_player_.set_clocking_hint_observer(this);
--- a/Machines/Utility/ROMCatalogue.cpp
+++ b/Machines/Utility/ROMCatalogue.cpp
@ -0,0 +1,482 @@
+//
+//  ROMCatalogue.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 01/06/2021.
+//  Copyright © 2021 Thomas Harte. All rights reserved.
+//
+
+#include "ROMCatalogue.hpp"
+
+#include <algorithm>
+#include <cassert>
+#include <codecvt>
+#include <iomanip>
+#include <locale>
+#include <sstream>
+
+using namespace ROM;
+
+namespace {
+constexpr Name MaxName = Name::SpectrumPlus3;
+}
+
+Request::Request(Name name, bool optional) {
+	node.name = name;
+	node.is_optional = optional;
+}
+
+Request Request::append(Node::Type type, const Request &rhs) {
+	// Start with the easiest case: this is already an appropriate
+	// request, and so is the new thing.
+	if(node.type == type && rhs.node.type == type) {
+		Request new_request = *this;
+		new_request.node.children.insert(new_request.node.children.end(), rhs.node.children.begin(), rhs.node.children.end());
+		new_request.node.sort();
+		return new_request;
+	}
+
+	// Possibly: left is appropriate request and rhs is just one more thing?
+	if(node.type == type && rhs.node.type == Node::Type::One) {
+		Request new_request = *this;
+		new_request.node.children.push_back(rhs.node);
+		new_request.node.sort();
+		return new_request;
+	}
+
+	// Or: right is appropriate request and this is just one more thing?
+	if(rhs.node.type == type && node.type == Node::Type::One) {
+		Request new_request = rhs;
+		new_request.node.children.push_back(node);
+		new_request.node.sort();
+		return new_request;
+	}
+
+	// Otherwise create a new parent node.
+	Request parent;
+	parent.node.type = type;
+	parent.node.children.push_back(this->node);
+	parent.node.children.push_back(rhs.node);
+	return parent;
+}
+
+Request Request::operator &&(const Request &rhs) {
+	return append(Node::Type::All, rhs);
+}
+
+Request Request::operator ||(const Request &rhs) {
+	return append(Node::Type::Any, rhs);
+}
+
+bool Request::validate(Map &map) const {
+	return node.validate(map);
+}
+
+std::vector<ROM::Description> Request::all_descriptions() const {
+	std::vector<Description> result;
+	node.add_descriptions(result);
+	return result;
+}
+
+void Request::Node::add_descriptions(std::vector<Description> &result) const {
+	if(type == Type::One) {
+		result.push_back(name);
+		return;
+	}
+
+	for(const auto &child: children) {
+		child.add_descriptions(result);
+	}
+}
+
+Request Request::subtract(const ROM::Map &map) const {
+	Request copy(*this);
+	if(copy.node.subtract(map)) {
+		copy.node.name = Name::None;
+		copy.node.type = Node::Type::One;
+	}
+	return copy;
+}
+
+bool Request::Node::subtract(const ROM::Map &map) {
+	switch(type) {
+		case Type::One:
+		return map.find(name) != map.end();
+
+		default: {
+			bool has_all = true;
+			bool has_any = false;
+
+			auto iterator = children.begin();
+			while(iterator != children.end()) {
+				const bool did_subtract = iterator->subtract(map);
+				has_all &= did_subtract;
+				has_any |= did_subtract;
+				if(did_subtract) {
+					iterator = children.erase(iterator);
+				} else {
+					++iterator;
+				}
+			}
+
+			return (type == Type::All && has_all) || (type == Type::Any && has_any);
+		}
+	}
+}
+
+bool Request::empty() {
+	return node.type == Node::Type::One && node.name == Name::None;
+}
+
+bool Request::Node::validate(Map &map) const {
+	// Leaf nodes are easy: check that the named ROM is present,
+	// unless it's optional, in which case it is always valid.
+	//
+	// If it is present, make sure it's the proper size.
+	if(type == Type::One) {
+		auto rom = map.find(name);
+		if(rom == map.end()) {
+			return is_optional;
+		}
+
+		const Description description(name);
+		rom->second.resize(description.size);
+
+		return true;
+	}
+
+	// This is a collection node then. Check for both any or all
+	// simultaneously, since all nodes will need to be visited
+	// regardless of any/all in order to ensure proper sizing.
+	bool has_all = true;
+	bool has_any = false;
+
+	for(const auto &child: children) {
+		const bool is_valid = child.validate(map);
+		has_all &= is_valid;
+		has_any |= is_valid;
+	}
+
+	return (type == Type::Any && has_any) || (type == Type::All && has_all);
+}
+
+void Request::visit(
+	const std::function<void(ListType, size_t)> &enter_list,
+	const std::function<void(void)> &exit_list,
+	const std::function<void(ROM::Request::ListType, const ROM::Description &, bool, size_t)> &add_item
+) const {
+	node.visit(enter_list, exit_list, add_item);
+}
+
+void Request::visit(
+	const std::function<void(LineItem, ListType, int, const ROM::Description *, bool, size_t)> &add_item
+) const {
+	int indentation_level = 0;
+	node.visit(
+		[&indentation_level, &add_item] (ROM::Request::ListType type, size_t size) {
+			add_item(LineItem::NewList, type, indentation_level, nullptr, false, size);
+			++indentation_level;
+		},
+		[&indentation_level] {
+			--indentation_level;
+		},
+		[&indentation_level, &add_item] (ROM::Request::ListType type, const ROM::Description &rom, bool is_optional, size_t remaining) {
+			add_item(LineItem::Description, type, indentation_level, &rom, is_optional, remaining);
+		}
+	);
+}
+
+void Request::Node::visit(
+	const std::function<void(ListType, size_t)> &enter_list,
+	const std::function<void(void)> &exit_list,
+	const std::function<void(ROM::Request::ListType type, const ROM::Description &, bool is_optional, size_t remaining)> &add_item
+) const {
+	switch(type) {
+		case Type::One:
+			enter_list(ListType::Single, 1);
+			add_item(ROM::Request::ListType::Any, Description(name), is_optional, 0);
+			exit_list();
+		break;
+
+		case Type::Any:
+		case Type::All: {
+			const ListType list_type = type == Type::Any ? ListType::Any : ListType::All;
+			enter_list(list_type, children.size());
+			for(size_t index = 0; index < children.size(); index++) {
+				auto &child = children[index];
+
+				if(child.type == Type::One) {
+					add_item(list_type, Description(child.name), child.is_optional, children.size() - 1 - index);
+				} else {
+					child.visit(enter_list, exit_list, add_item);
+				}
+			}
+			exit_list();
+		} break;
+	}
+}
+
+std::vector<Description> ROM::all_descriptions() {
+	std::vector<Description> result;
+	for(int name = 1; name <= MaxName; name++) {
+		result.push_back(Description(ROM::Name(name)));
+	}
+	return result;
+}
+
+std::optional<Description> Description::from_crc(uint32_t crc32) {
+	for(int name = 1; name <= MaxName; name++) {
+		const Description candidate = Description(ROM::Name(name));
+
+		const auto found_crc = std::find(candidate.crc32s.begin(), candidate.crc32s.end(), crc32);
+		if(found_crc != candidate.crc32s.end()) {
+			return candidate;
+		}
+	}
+
+	return std::nullopt;
+}
+
+std::string Description::description(int flags) const {
+	std::stringstream output;
+
+	// If there are no CRCs, don't output them.
+	if(crc32s.empty()) flags &= ~ DescriptionFlag::CRC;
+
+	// Print the file name(s) and the descriptive name.
+	if(flags & DescriptionFlag::Filename) {
+		flags &= ~DescriptionFlag::Filename;
+
+		output << machine_name <<  '/';
+		if(file_names.size() == 1) {
+			output << file_names[0];
+		} else {
+			output << "{";
+			bool is_first = true;
+			for(const auto &file_name: file_names) {
+				if(!is_first) output << " or ";
+				output << file_name;
+				is_first = false;
+			}
+			output << "}";
+		}
+		output << " (" << descriptive_name;
+		if(!flags) {
+			output << ")";
+			return output.str();
+		}
+		output << "; ";
+	} else {
+		output << descriptive_name;
+		if(!flags) {
+			return output.str();
+		}
+		output << " (";
+	}
+
+	// Print the size.
+	if(flags & DescriptionFlag::Size) {
+		flags &= ~DescriptionFlag::Size;
+		output << size << " bytes";
+
+		if(!flags) {
+			output << ")";
+			return output.str();
+		}
+		output << "; ";
+	}
+
+	// Print the CRC(s).
+	if(flags & DescriptionFlag::CRC) {
+		flags &= ~DescriptionFlag::CRC;
+
+		output << ((crc32s.size() > 1) ? "usual crc32s: " : "usual crc32: ");
+		bool is_first = true;
+		for(const auto crc32: crc32s) {
+			if(!is_first) output << ", ";
+			is_first = false;
+			output << std::hex << std::setfill('0') << std::setw(8) << crc32;
+		}
+
+		if(!flags) {
+			output << ")";
+			return output.str();
+		}
+	}
+
+	return output.str();
+}
+
+std::wstring Request::description(int description_flags, wchar_t bullet_point) {
+	std::wstringstream output;
+	std::wstring_convert<std::codecvt_utf8<wchar_t>> wstring_converter;
+
+	visit(
+		[&output, description_flags, bullet_point, &wstring_converter] (ROM::Request::LineItem item, ROM::Request::ListType type, int indentation_level, const ROM::Description *description, bool is_optional, size_t remaining) {
+			if(indentation_level) {
+				output << std::endl;
+				for(int c = 0; c < indentation_level; c++) output << '\t';
+				output << bullet_point << ' ';
+			}
+
+			switch(item) {
+				case ROM::Request::LineItem::NewList:
+					if(remaining > 1) {
+						if(!indentation_level) output << " ";
+						switch(type) {
+							default:
+							case ROM::Request::ListType::All:	output << "all of:";		break;
+							case ROM::Request::ListType::Any:
+								if(remaining == 2) {
+									output << "either of:";
+								} else {
+									output << "any of:";
+								}
+							break;
+						}
+					} else {
+						output << ":";
+					}
+				break;
+
+				case ROM::Request::LineItem::Description:
+					if(is_optional) output << "optionally, ";
+
+					output << wstring_converter.from_bytes(description->description(description_flags));
+
+					if(remaining) {
+						output << ";";
+						if(remaining == 1) {
+							output << ((type == ROM::Request::ListType::All) ? " and" : " or");
+						}
+					} else {
+						output << ".";
+					}
+				break;
+			}
+		}
+	);
+
+	return output.str();
+}
+
+
+Description::Description(Name name) {
+	switch(name) {
+		default: assert(false);	break;
+
+		case Name::AMSDOS:				*this = Description(name, "AmstradCPC", "the Amstrad Disk Operating System", "amsdos.rom", 16*1024, 0x1fe22ecdu);	break;
+		case Name::CPC464Firmware:		*this = Description(name, "AmstradCPC", "the CPC 464 firmware", "os464.rom", 16*1024, 0x815752dfu);					break;
+		case Name::CPC464BASIC:			*this = Description(name, "AmstradCPC", "the CPC 464 BASIC ROM", "basic464.rom", 16*1024, 0x7d9a3bacu);				break;
+		case Name::CPC664Firmware:		*this = Description(name, "AmstradCPC", "the CPC 664 firmware", "os664.rom", 16*1024, 0x3f5a6dc4u);					break;
+		case Name::CPC664BASIC:			*this = Description(name, "AmstradCPC", "the CPC 664 BASIC ROM", "basic664.rom", 16*1024, 0x32fee492u);				break;
+		case Name::CPC6128Firmware:		*this = Description(name, "AmstradCPC", "the CPC 6128 firmware", "os6128.rom", 16*1024, 0x0219bb74u);				break;
+		case Name::CPC6128BASIC:		*this = Description(name, "AmstradCPC", "the CPC 6128 BASIC ROM", "basic6128.rom", 16*1024, 0xca6af63du);			break;
+
+		case Name::AppleIIEnhancedE:	*this = Description(name, "AppleII", "the Enhanced Apple IIe ROM", "apple2e.rom", 32*1024, 0x65989942u);				break;
+		case Name::AppleIIe:			*this = Description(name, "AppleII", "the Apple IIe ROM", "apple2eu.rom", 32*1024, 0xe12be18du);						break;
+		case Name::AppleIIPlus:			*this = Description(name, "AppleII", "the Apple II+ ROM", "apple2.rom", 12*1024, 0xf66f9c26u);							break;
+		case Name::AppleIIOriginal:		*this = Description(name, "AppleII", "the original Apple II ROM", "apple2o.rom", 12*1024, 0xba210588u);					break;
+		case Name::AppleIICharacter:	*this = Description(name, "AppleII", "the basic Apple II character ROM", "apple2-character.rom", 2*1024, 0x64f415c6u);	break;
+		case Name::AppleIIeCharacter:	*this = Description(name, "AppleII", "the Apple IIe character ROM", "apple2eu-character.rom", 4*1024, 0x816a86f1u);		break;
+		case Name::AppleIIEnhancedECharacter:
+			*this = Description(name, "AppleII", "the Enhanced Apple IIe character ROM", "apple2e-character.rom", 4*1024, 0x2651014du);
+		break;
+
+		case Name::AppleIIgsROM00:	/* TODO */
+		case Name::AppleIIgsROM01:		*this = Description(name, "AppleIIgs", "the Apple IIgs ROM01", "apple2gs.rom", 128*1024, 0x42f124b0u);			break;
+		case Name::AppleIIgsROM03:		*this = Description(name, "AppleIIgs", "the Apple IIgs ROM03", "apple2gs.rom2", 256*1024, 0xde7ddf29u);			break;
+		case Name::AppleIIgsCharacter:	*this = Description(name, "AppleIIgs", "the Apple IIgs character ROM", "apple2gs.chr", 4*1024, 0x91e53cd8u);	break;
+		case AppleIIgsMicrocontrollerROM03:
+			*this = Description(name, "AppleIIgs", "the Apple IIgs ROM03 ADB microcontroller ROM", "341s0632-2", 4*1024, 0xe1c11fb0u);
+		break;
+
+		case Name::DiskIIBoot16Sector:
+			*this = Description(name, "DiskII", "the Disk II 16-sector boot ROM", "boot-16.rom", 256, 0xce7144f6u);
+		break;
+		case Name::DiskIIStateMachine16Sector:
+			*this = Description(name, "DiskII", "the Disk II 16-sector state machine ROM", "state-machine-16.rom", 256, std::initializer_list<uint32_t>{ 0x9796a238, 0xb72a2c70 } );
+		break;
+		case Name::DiskIIBoot13Sector:
+			*this = Description(name, "DiskII", "the Disk II 13-sector boot ROM", "boot-13.rom", 256, 0xd34eb2ffu);
+		break;
+		case Name::DiskIIStateMachine13Sector:
+			*this = Description(name, "DiskII", "the Disk II 13-sector state machine ROM", "state-machine-13.rom", 256, 0x62e22620u);
+		break;
+
+		case Name::Macintosh128k:	*this = Description(name, "Macintosh", "the Macintosh 128k ROM", "mac128k.rom", 64*1024, 0x6d0c8a28u);	break;
+		case Name::Macintosh512k:	*this = Description(name, "Macintosh", "the Macintosh 512k ROM", "mac512k.rom", 64*1024, 0xcf759e0d);	break;
+		case Name::MacintoshPlus: {
+			const std::initializer_list<uint32_t> crcs = { 0x4fa5b399, 0x7cacd18f, 0xb2102e8e };
+			*this = Description(name, "Macintosh", "the Macintosh Plus ROM", "macplus.rom", 128*1024, crcs);
+		} break;
+
+		case Name::AtariSTTOS100:		*this = Description(name, "AtariST", "the UK TOS 1.00 ROM", "tos100.img", 192*1024, 0x1a586c64u);		break;
+		case Name::AtariSTTOS104:		*this = Description(name, "AtariST", "the UK TOS 1.04 ROM", "tos104.img", 192*1024, 0xa50d1d43u);		break;
+		case Name::AtariSTEmuTOS192:	*this = Description(name, "AtariST", "the UK EmuTOS 1.92 ROM", "etos192uk.img", 192*1024, 0xfc3b9e61u);	break;
+
+		case Name::ColecoVisionBIOS:
+			*this = Description(name, "ColecoVision", "the ColecoVision BIOS", "coleco.rom", 8*1024, 0x3aa93ef3u);
+		break;
+
+		case Name::ZX80:	*this = Description(name, "ZX8081", "the ZX80 BASIC ROM", "zx80.rom", 4 * 1024, 0x4c7fc597u);	break;
+		case Name::ZX81:	*this = Description(name, "ZX8081", "the ZX81 BASIC ROM", "zx81.rom", 8 * 1024, 0x4b1dd6ebu);	break;
+
+		case Name::Spectrum48k:		*this = Description(name, "ZXSpectrum", "the 48kb ROM", "48.rom", 16 * 1024, 0xddee531fu);		break;
+		case Name::Spectrum128k:	*this = Description(name, "ZXSpectrum", "the 128kb ROM", "128.rom", 32 * 1024, 0x2cbe8995u);	break;
+		case Name::SpecrumPlus2:	*this = Description(name, "ZXSpectrum", "the +2 ROM", "plus2.rom", 32 * 1024, 0xe7a517dcu); 	break;
+		case Name::SpectrumPlus3: {
+			const std::initializer_list<uint32_t> crcs = { 0x96e3c17a, 0xbe0d9ec4 };
+			*this = Description(name, "ZXSpectrum", "the +2a/+3 ROM", "plus3.rom", 64 * 1024, crcs);
+		} break;
+
+		case Name::AcornBASICII:	*this = Description(name, "Electron", "the Acorn BASIC II ROM", "basic.rom", 16*1024, 0x79434781u); 			break;
+		case Name::PRESADFSSlot1:	*this = Description(name, "Electron", "the E00 ADFS ROM, first slot", "ADFS-E00_1.rom", 16*1024, 0x51523993u); 	break;
+		case Name::PRESADFSSlot2:	*this = Description(name, "Electron", "the E00 ADFS ROM, second slot", "ADFS-E00_2.rom", 16*1024, 0x8d17de0eu); break;
+		case Name::AcornADFS:		*this = Description(name, "Electron", "the Acorn ADFS ROM", "adfs.rom", 16*1024, 0x3289bdc6u); 					break;
+		case Name::Acorn1770DFS:	*this = Description(name, "Electron", "the 1770 DFS ROM", "DFS-1770-2.20.rom", 16*1024, 0xf3dc9bc5u);			break;
+		case Name::PRESAdvancedPlus6:
+			*this = Description(name, "Electron", "the 8kb Advanced Plus 6 ROM", "AP6v133.rom", 8*1024, 0xe0013cfcu);
+		break;
+		case Name::AcornElectronMOS100:
+			*this = Description(name, "Electron", "the Electron MOS ROM v1.00", "os.rom", 16*1024, 0xbf63fb1fu);
+		break;
+
+		case Name::MasterSystemJapaneseBIOS:	*this = Description(name, "MasterSystem", "the Japanese Master System BIOS", "japanese-bios.sms", 8*1024, 0x48d44a13u); break;
+		case Name::MasterSystemWesternBIOS:		*this = Description(name, "MasterSystem", "the European/US Master System BIOS", "bios.sms", 8*1024, 0x0072ed54u); 		break;
+
+		case Name::Commodore1540:	*this = Description(name, "Commodore1540", "the 1540 ROM", "1540.bin", 16*1024, 0x718d42b1u);	break;
+		case Name::Commodore1541:	*this = Description(name, "Commodore1540", "the 1541 ROM", "1541.bin", 16*1024, 0xfb760019);	break;
+
+		case Name::Vic20BASIC:				*this = Description(name, "Vic20", "the VIC-20 BASIC ROM", "basic.bin", 8*1024, 0xdb4c43c1u);									break;
+		case Name::Vic20EnglishCharacters:	*this = Description(name, "Vic20", "the English-language VIC-20 character ROM", "characters-english.bin", 4*1024, 0x83e032a6u);	break;
+		case Name::Vic20EnglishPALKernel:	*this = Description(name, "Vic20", "the English-language PAL VIC-20 kernel ROM", "kernel-pal.bin", 8*1024, 0x4be07cb4u);		break;
+		case Name::Vic20EnglishNTSCKernel:	*this = Description(name, "Vic20", "the English-language NTSC VIC-20 kernel ROM", "kernel-ntsc.bin", 8*1024, 0xe5e7c174u);		break;
+		case Name::Vic20DanishCharacters:	*this = Description(name, "Vic20", "the Danish VIC-20 character ROM", "characters-danish.bin", 4*1024, 0x7fc11454u);			break;
+		case Name::Vic20DanishKernel:		*this = Description(name, "Vic20", "the Danish VIC-20 kernel ROM", "kernel-danish.bin", 8*1024, 0x02adaf16u);					break;
+		case Name::Vic20JapaneseCharacters:	*this = Description(name, "Vic20", "the Japanese VIC-20 character ROM", "characters-japanese.bin", 4*1024, 0xfcfd8a4bu);		break;
+		case Name::Vic20JapaneseKernel:		*this = Description(name, "Vic20", "the Japanese VIC-20 kernel ROM", "kernel-japanese.bin", 8*1024, 0x336900d7u);				break;
+		case Name::Vic20SwedishCharacters:	*this = Description(name, "Vic20", "the Swedish VIC-20 character ROM", "characters-swedish.bin", 4*1024, 0xd808551du);			break;
+		case Name::Vic20SwedishKernel:		*this = Description(name, "Vic20", "the Swedish VIC-20 kernel ROM", "kernel-swedish.bin", 8*1024, 0xb2a60662u);					break;
+
+		case Name::OricColourROM:		*this = Description(name, "Oric", "the Oric colour ROM", "colour.rom", 128, 0xd50fca65u);			break;
+		case Name::OricBASIC10:			*this = Description(name, "Oric", "Oric BASIC 1.0", "basic10.rom", 16*1024, 0xf18710b4u);			break;
+		case Name::OricBASIC11:			*this = Description(name, "Oric", "Oric BASIC 1.1", "basic11.rom", 16*1024, 0xc3a92befu);			break;
+		case Name::OricPravetzBASIC:	*this = Description(name, "Oric", "Pravetz BASIC", "pravetz.rom", 16*1024, 0x58079502u);			break;
+		case Name::OricByteDrive500:	*this = Description(name, "Oric", "the Oric Byte Drive 500 ROM", "bd500.rom", 8*1024, 0x61952e34u);	break;
+		case Name::OricJasmin:			*this = Description(name, "Oric", "the Oric Jasmin ROM", "jasmin.rom", 2*1024, 0x37220e89u);		break;
+		case Name::OricMicrodisc:		*this = Description(name, "Oric", "the Oric Microdisc ROM", "microdisc.rom", 8*1024, 0xa9664a9cu);	break;
+		case Name::Oric8DOSBoot:		*this = Description(name, "Oric", "the 8DOS boot ROM", "8dos.rom", 512, 0x49a74c06u);				break;
+
+		case Name::MSXGenericBIOS:	*this = Description(name, "MSX", "any MSX BIOS", "msx.rom", 32*1024, 0x94ee12f3u);					break;
+		case Name::MSXJapaneseBIOS:	*this = Description(name, "MSX", "a Japanese MSX BIOS", "msx-japanese.rom", 32*1024, 0xee229390u);	break;
+		case Name::MSXAmericanBIOS:	*this = Description(name, "MSX", "an American MSX BIOS", "msx-american.rom", 32*1024, 0u);			break;
+		case Name::MSXEuropeanBIOS:	*this = Description(name, "MSX", "a European MSX BIOS", "msx-european.rom", 32*1024, 0u);			break;
+		case Name::MSXDOS:			*this = Description(name, "MSX", "the MSX-DOS ROM", "disk.rom", 16*1024, 0x721f61dfu);				break;
+
+		case Name::SinclairQLJS:
+			*this = Description(name, "SinclairQL", "the Sinclair QL 'JS' ROM", "js.rom", 48*1024, 0x0f95aab5u);
+		break;
+
+	}
+}
--- a/Machines/Utility/ROMCatalogue.hpp
+++ b/Machines/Utility/ROMCatalogue.hpp
@ -0,0 +1,269 @@
+//
+//  ROMCatalogue.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 01/06/2021.
+//  Copyright © 2021 Thomas Harte. All rights reserved.
+//
+
+#ifndef ROMCatalogue_hpp
+#define ROMCatalogue_hpp
+
+#include <algorithm>
+#include <functional>
+#include <map>
+#include <optional>
+#include <set>
+#include <string>
+#include <vector>
+
+namespace ROM {
+
+enum Name {
+	None,
+
+	// Acorn.
+	AcornBASICII,
+	AcornElectronMOS100,
+	PRESADFSSlot1,
+	PRESADFSSlot2,
+	AcornADFS,
+	PRESAdvancedPlus6,
+	Acorn1770DFS,
+
+	// Amstrad CPC.
+	AMSDOS,
+	CPC464Firmware,		CPC464BASIC,
+	CPC664Firmware,		CPC664BASIC,
+	CPC6128Firmware,	CPC6128BASIC,
+
+	// Apple II.
+	AppleIIOriginal,
+	AppleIIPlus,
+	AppleIICharacter,
+	AppleIIe,
+	AppleIIeCharacter,
+	AppleIIEnhancedE,
+	AppleIIEnhancedECharacter,
+
+	// Apple IIgs.
+	AppleIIgsROM00,
+	AppleIIgsROM01,
+	AppleIIgsROM03,
+	AppleIIgsMicrocontrollerROM03,
+	AppleIIgsCharacter,
+
+	// Atari ST.
+	AtariSTTOS100,
+	AtariSTTOS104,
+	AtariSTEmuTOS192,
+
+	// ColecoVision.
+	ColecoVisionBIOS,
+
+	// Commodore 1540/1541.
+	Commodore1540,
+	Commodore1541,
+
+	// Disk II.
+	DiskIIStateMachine16Sector,
+	DiskIIBoot16Sector,
+	DiskIIStateMachine13Sector,
+	DiskIIBoot13Sector,
+
+	// Macintosh.
+	Macintosh128k,
+	Macintosh512k,
+	MacintoshPlus,
+
+	// Master System.
+	MasterSystemJapaneseBIOS,
+	MasterSystemWesternBIOS,
+
+	// MSX.
+	MSXGenericBIOS,
+	MSXJapaneseBIOS,
+	MSXAmericanBIOS,
+	MSXEuropeanBIOS,
+	MSXDOS,
+
+	// Oric.
+	OricColourROM,
+	OricBASIC10,
+	OricBASIC11,
+	OricPravetzBASIC,
+	OricByteDrive500,
+	OricJasmin,
+	OricMicrodisc,
+	Oric8DOSBoot,
+
+	// Sinclair QL.
+	SinclairQLJS,
+
+	// Vic-20.
+	Vic20BASIC,
+	Vic20EnglishCharacters,
+	Vic20EnglishPALKernel,
+	Vic20EnglishNTSCKernel,
+	Vic20DanishCharacters,
+	Vic20DanishKernel,
+	Vic20JapaneseCharacters,
+	Vic20JapaneseKernel,
+	Vic20SwedishCharacters,
+	Vic20SwedishKernel,
+
+	// ZX80/81.
+	ZX80,
+	ZX81,
+
+	// ZX Spectrum.
+	Spectrum48k,
+	Spectrum128k,
+	SpecrumPlus2,
+	SpectrumPlus3,
+
+};
+
+using Map = std::map<ROM::Name, std::vector<uint8_t>>;
+
+struct Description {
+	/// The ROM's enum name.
+	Name name = Name::None;
+	/// The machine with which this ROM is associated, in a form that is safe for using as
+	/// part of a file name.
+	std::string machine_name;
+	/// A descriptive name for this ROM, suitable for use in a bullet-point list, a bracket
+	/// clause, etc, e.g. "the Electron MOS 1.0".
+	std::string descriptive_name;
+	/// All idiomatic file name for this ROM, e.g. "os10.rom".
+	std::vector<std::string> file_names;
+	/// The expected size of this ROM in bytes, e.g. 32768.
+	size_t size = 0;
+	/// CRC32s for all known acceptable copies of this ROM; intended to allow a host platform
+	/// to test user-provided ROMs of unknown provenance. **Not** intended to be used
+	/// to exclude ROMs where the user's intent is otherwise clear.
+	std::set<uint32_t> crc32s;
+
+	/// Constructs the @c Description that correlates to @c name.
+	Description(Name name);
+
+	/// Constructs the @c Description that correlates to @c crc32, if any.
+	static std::optional<Description> from_crc(uint32_t crc32);
+
+	enum DescriptionFlag {
+		Size = 1 << 0,
+		CRC = 1 << 1,
+		Filename = 1 << 2,
+	};
+
+	/// Provides a single-line of text describing this ROM, including the usual base text
+	/// plus all the fields provided as @c flags .
+	std::string description(int flags) const;
+
+	private:
+		template <typename FileNameT, typename CRC32T> Description(
+			Name name, std::string machine_name, std::string descriptive_name, FileNameT file_names, size_t size, CRC32T crc32s = uint32_t(0)
+		) : name{name}, machine_name{machine_name}, descriptive_name{descriptive_name}, file_names{file_names}, size{size}, crc32s{crc32s} {
+			// Slightly lazy: deal with the case where the constructor wasn't provided with any
+			// CRCs by spotting that the set has exactly one member, which has value 0. The alternative
+			// would be to provide a partial specialisation that never put anything into the set.
+			if(this->crc32s.size() == 1 && !*this->crc32s.begin()) {
+				this->crc32s.clear();
+			}
+		}
+};
+
+/// @returns a vector of all possible instances of ROM::Description — i.e. descriptions of every ROM
+/// currently known to the ROM catalogue.
+std::vector<Description> all_descriptions();
+
+struct Request {
+	Request(Name name, bool optional = false);
+	Request() {}
+
+	/// Forms the request that would be satisfied by @c this plus the right-hand side.
+	Request operator &&(const Request &);
+
+	/// Forms the request that would be satisfied by either @c this or the right-hand side.
+	Request operator ||(const Request &);
+
+	/// Inspects the ROMMap to ensure that it satisfies this @c Request.
+	/// @c returns @c true if the request is satisfied; @c false otherwise.
+	///
+	/// All ROMs in the map will be resized to their idiomatic sizes.
+	bool validate(Map &) const;
+
+	/// Returns a flattened array of all @c ROM::Descriptions that relate to anything
+	/// anywhere in this ROM request.
+	std::vector<Description> all_descriptions() const;
+
+	/// @returns @c true if this request is empty, i.e. would be satisfied with no ROMs; @c false otherwise.
+	bool empty();
+
+	/// @returns what remains of this ROM request given that everything in @c map has been found.
+	Request subtract(const ROM::Map &map) const;
+
+	enum class ListType {
+		Any, All, Single
+	};
+	void visit(
+		const std::function<void(ListType, size_t size)> &enter_list,
+		const std::function<void(void)> &exit_list,
+		const std::function<void(ROM::Request::ListType type, const ROM::Description &, bool is_optional, size_t remaining)> &add_item
+	) const;
+
+	enum class LineItem {
+		NewList, Description
+	};
+	void visit(
+		const std::function<void(LineItem, ListType, int level, const ROM::Description *, bool is_optional, size_t remaining)> &add_item
+	) const;
+
+	/// @returns a full bullet-pointed list of the requirements of this request, including
+	/// appropriate conjuntives. This text is intended to be glued to the end of an opening
+	/// portion of a sentence, e.g. "Please supply" + request.description(0, L'*').
+	std::wstring description(int description_flags, wchar_t bullet_point);
+
+	private:
+		struct Node {
+			enum class Type {
+				Any, All, One
+			};
+			Type type = Type::One;
+			Name name = Name::None;
+			/// @c true if this ROM is optional for machine startup. Generally indicates something
+			/// that would make emulation more accurate, but not sufficiently so to make it
+			/// a necessity.
+			bool is_optional = false;
+			std::vector<Node> children;
+
+			void add_descriptions(std::vector<Description> &) const;
+			bool validate(Map &) const;
+			void visit(
+				const std::function<void(ListType, size_t)> &enter_list,
+				const std::function<void(void)> &exit_list,
+				const std::function<void(ROM::Request::ListType type, const ROM::Description &, bool is_optional, size_t remaining)> &add_item
+			) const;
+			bool subtract(const ROM::Map &map);
+			void sort() {
+				// Don't do a full sort, but move anything optional to the back.
+				// This makes them print more nicely; it's a human-facing tweak only.
+				ssize_t index = ssize_t(children.size() - 1);
+				bool has_seen_non_optional = false;
+				while(index >= 0) {
+					has_seen_non_optional |= !children[size_t(index)].is_optional;
+					if(children[size_t(index)].is_optional && has_seen_non_optional) {
+						std::rotate(children.begin() + index, children.begin() + index + 1, children.end());
+					}
+					--index;
+				}
+			}
+		};
+		Node node;
+
+		Request append(Node::Type type, const Request &rhs);
+};
+
+}
+
+#endif /* ROMCatalogue_hpp */
--- a/Signal.xcodeproj/project.pbxproj
+++ b/Signal.xcodeproj/project.pbxproj
@ -12,6 +12,11 @@
 		4B0333AF2094081A0050B93D /* AppleDSK.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B0333AD2094081A0050B93D /* AppleDSK.cpp */; };
 		4B0333B02094081A0050B93D /* AppleDSK.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B0333AD2094081A0050B93D /* AppleDSK.cpp */; };
 		4B049CDD1DA3C82F00322067 /* BCDTest.swift in Sources */ = {isa = PBXBuildFile; fileRef = 4B049CDC1DA3C82F00322067 /* BCDTest.swift */; };
+		4B051C912669C90B00CA44E8 /* ROMCatalogue.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B051C5826670A9300CA44E8 /* ROMCatalogue.cpp */; };
+		4B051C922669C90B00CA44E8 /* ROMCatalogue.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B051C5826670A9300CA44E8 /* ROMCatalogue.cpp */; };
+		4B051C93266D9D6900CA44E8 /* ROMImages in Resources */ = {isa = PBXBuildFile; fileRef = 4BC9DF441D044FCA00F44158 /* ROMImages */; };
+		4B051C95266EF50200CA44E8 /* AppleIIOptionsPanel.swift in Sources */ = {isa = PBXBuildFile; fileRef = 4B051C94266EF50200CA44E8 /* AppleIIOptionsPanel.swift */; };
+		4B051C97266EF5F600CA44E8 /* CSAppleII.mm in Sources */ = {isa = PBXBuildFile; fileRef = 4B051C96266EF5F600CA44E8 /* CSAppleII.mm */; };
 		4B05401E219D1618001BF69C /* ScanTarget.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B05401D219D1618001BF69C /* ScanTarget.cpp */; };
 		4B05401F219D1618001BF69C /* ScanTarget.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B05401D219D1618001BF69C /* ScanTarget.cpp */; };
 		4B055A7A1FAE78A00060FFFF /* SDL2.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 4B055A771FAE78210060FFFF /* SDL2.framework */; };
@ -566,7 +571,6 @@
 		4B9F11CA2272433900701480 /* libz.tbd in Frameworks */ = {isa = PBXBuildFile; fileRef = 4B69FB451C4D950F00B5F0AA /* libz.tbd */; };
 		4B9F11CC22729B3600701480 /* OPCLOGR2.BIN in Resources */ = {isa = PBXBuildFile; fileRef = 4B9F11CB22729B3500701480 /* OPCLOGR2.BIN */; };
 		4BA0F68E1EEA0E8400E9489E /* ZX8081.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BA0F68C1EEA0E8400E9489E /* ZX8081.cpp */; };
-		4BA3189422E7A4CA00D18CFA /* ROMImages in Resources */ = {isa = PBXBuildFile; fileRef = 4BC9DF441D044FCA00F44158 /* ROMImages */; };
 		4BA61EB01D91515900B3C876 /* NSData+StdVector.mm in Sources */ = {isa = PBXBuildFile; fileRef = 4BA61EAF1D91515900B3C876 /* NSData+StdVector.mm */; };
 		4BA91E1D216D85BA00F79557 /* MasterSystemVDPTests.mm in Sources */ = {isa = PBXBuildFile; fileRef = 4BA91E1C216D85BA00F79557 /* MasterSystemVDPTests.mm */; };
 		4BAD13441FF709C700FD114A /* MSX.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B0E61051FF34737002A9DBD /* MSX.cpp */; };
@ -1019,6 +1023,11 @@
 		4B047075201ABC180047AB0D /* Cartridge.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = Cartridge.hpp; sourceTree = "<group>"; };
 		4B049CDC1DA3C82F00322067 /* BCDTest.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = BCDTest.swift; sourceTree = "<group>"; };
 		4B04B65622A58CB40006AB58 /* Target.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = Target.hpp; sourceTree = "<group>"; };
+		4B051C5826670A9300CA44E8 /* ROMCatalogue.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = ROMCatalogue.cpp; sourceTree = "<group>"; };
+		4B051C5926670A9300CA44E8 /* ROMCatalogue.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = ROMCatalogue.hpp; sourceTree = "<group>"; };
+		4B051C94266EF50200CA44E8 /* AppleIIOptionsPanel.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = AppleIIOptionsPanel.swift; sourceTree = "<group>"; };
+		4B051C96266EF5F600CA44E8 /* CSAppleII.mm */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.objcpp; path = CSAppleII.mm; sourceTree = "<group>"; };
+		4B051C98266EF60500CA44E8 /* CSAppleII.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = CSAppleII.h; sourceTree = "<group>"; };
 		4B05401D219D1618001BF69C /* ScanTarget.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = ScanTarget.cpp; sourceTree = "<group>"; };
 		4B055A6A1FAE763F0060FFFF /* Clock Signal Kiosk */ = {isa = PBXFileReference; explicitFileType = "compiled.mach-o.executable"; includeInIndex = 0; path = "Clock Signal Kiosk"; sourceTree = BUILT_PRODUCTS_DIR; };
 		4B055A771FAE78210060FFFF /* SDL2.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = SDL2.framework; path = ../../../../Library/Frameworks/SDL2.framework; sourceTree = SOURCE_ROOT; };
@ -2401,8 +2410,10 @@
 		4B2A53981D117D36003C6002 /* Wrappers */ = {
 			isa = PBXGroup;
 			children = (
+				4B051C98266EF60500CA44E8 /* CSAppleII.h */,
 				4B2A53991D117D36003C6002 /* CSAtari2600.h */,
 				4B14978D1EE4B4D200CE2596 /* CSZX8081.h */,
+				4B051C96266EF5F600CA44E8 /* CSAppleII.mm */,
 				4B2A539A1D117D36003C6002 /* CSAtari2600.mm */,
 				4B14978E1EE4B4D200CE2596 /* CSZX8081.mm */,
 			);
@ -2415,11 +2426,13 @@
 				4B055ABE1FAE98000060FFFF /* MachineForTarget.cpp */,
 				4B2B3A481F9B8FA70062DABF /* MemoryFuzzer.cpp */,
 				4BCE005B227D30CC000CA200 /* MemoryPacker.cpp */,
+				4B051C5826670A9300CA44E8 /* ROMCatalogue.cpp */,
 				4B17B58920A8A9D9007CCA8F /* StringSerialiser.cpp */,
 				4B2B3A471F9B8FA70062DABF /* Typer.cpp */,
 				4B055ABF1FAE98000060FFFF /* MachineForTarget.hpp */,
 				4B2B3A491F9B8FA70062DABF /* MemoryFuzzer.hpp */,
 				4BCE005C227D30CC000CA200 /* MemoryPacker.hpp */,
+				4B051C5926670A9300CA44E8 /* ROMCatalogue.hpp */,
 				4B17B58A20A8A9D9007CCA8F /* StringSerialiser.hpp */,
 				4B79A4FE1FC9082300EEDAD5 /* TypedDynamicMachine.hpp */,
 				4B2B3A4A1F9B8FA70062DABF /* Typer.hpp */,
@ -2771,6 +2784,7 @@
 		4B55CE551C3B7D360093A61B /* Documents */ = {
 			isa = PBXGroup;
 			children = (
+				4B051C94266EF50200CA44E8 /* AppleIIOptionsPanel.swift */,
 				4B8FE21F1DA19D7C0090D3CE /* Atari2600OptionsPanel.swift */,
 				4B55CE5E1C3B7D960093A61B /* MachineDocument.swift */,
 				4B8FE2211DA19FB20090D3CE /* MachinePanel.swift */,
@ -4762,7 +4776,7 @@
 				4BB73EAC1B587A5100552FC2 /* MainMenu.xib in Resources */,
 				4B8FE21D1DA19D5F0090D3CE /* QuickLoadCompositeOptions.xib in Resources */,
 				4B49F0A923346F7A0045E6A6 /* MacintoshOptions.xib in Resources */,
-				4BA3189422E7A4CA00D18CFA /* ROMImages in Resources */,
+				4B051C93266D9D6900CA44E8 /* ROMImages in Resources */,
 				4B79E4461E3AF38600141F11 /* floppy525.png in Resources */,
 				4BEEE6BD20DC72EB003723BF /* CompositeOptions.xib in Resources */,
 				4B1497981EE4B97F00CE2596 /* ZX8081Options.xib in Resources */,
@ -5321,6 +5335,7 @@
 				4BB0A65C2044FD3000FB3688 /* SN76489.cpp in Sources */,
 				4B595FAE2086DFBA0083CAA8 /* AudioToggle.cpp in Sources */,
 				4B0F1C242605996900B85C66 /* ZXSpectrumTAP.cpp in Sources */,
+				4B051C912669C90B00CA44E8 /* ROMCatalogue.cpp in Sources */,
 				4B055AB91FAE86170060FFFF /* Acorn.cpp in Sources */,
 				4B302185208A550100773308 /* DiskII.cpp in Sources */,
 				4B0F1BB32602645900B85C66 /* StaticAnalyser.cpp in Sources */,
@ -5395,11 +5410,13 @@
 				4B4518861F75E91A00926311 /* MFMDiskController.cpp in Sources */,
 				4B0ACC2C23775819008902D0 /* IntelligentKeyboard.cpp in Sources */,
 				4B92E26A234AE35100CD6D1B /* MFP68901.cpp in Sources */,
+				4B051C97266EF5F600CA44E8 /* CSAppleII.mm in Sources */,
 				4B0ACC2A23775819008902D0 /* Video.cpp in Sources */,
 				4B54C0BF1F8D8F450050900F /* Keyboard.cpp in Sources */,
 				4B3FE75E1F3CF68B00448EE4 /* CPM.cpp in Sources */,
 				4B2BFDB21DAEF5FF001A68B8 /* Video.cpp in Sources */,
 				4BEDA3BF25B25563000C2DBD /* Decoder.cpp in Sources */,
+				4B051C95266EF50200CA44E8 /* AppleIIOptionsPanel.swift in Sources */,
 				4B4DC82B1D2C27A4003C5BF8 /* SerialBus.cpp in Sources */,
 				4BE8EB6625C750B50040BC40 /* DAT.cpp in Sources */,
 				4BBFFEE61F7B27F1005F3FEB /* TrackSerialiser.cpp in Sources */,
@ -5537,6 +5554,7 @@
 				4B15A9FC208249BB005E6C8D /* StaticAnalyser.cpp in Sources */,
 				4B5FADC01DE3BF2B00AEC565 /* Microdisc.cpp in Sources */,
 				4B0F1BDA2602FF9800B85C66 /* Video.cpp in Sources */,
+				4B051C922669C90B00CA44E8 /* ROMCatalogue.cpp in Sources */,
 				4B54C0C81F8D91E50050900F /* Keyboard.cpp in Sources */,
 				4B79A5011FC913C900EEDAD5 /* MSX.cpp in Sources */,
 				4BEE0A701D72496600532C7B /* PRG.cpp in Sources */,
--- a/Signal.xcodeproj/xcshareddata/xcschemes/Clock
+++ b/Signal.xcodeproj/xcshareddata/xcschemes/Clock
@ -56,6 +56,18 @@
            argument = "/Users/thomasharte/Downloads/test-dsk-for-rw-and-50-60-hz/TEST-RW-60Hz.DSK"
            isEnabled = "NO">
         </CommandLineArgument>
+         <CommandLineArgument
+            argument = "&quot;/Users/thomasharte/Desktop/Soft/Apple II/WOZs/Prince of Persia side A.woz&quot;"
+            isEnabled = "YES">
+         </CommandLineArgument>
+         <CommandLineArgument
+            argument = "--rompath=~/ROMs"
+            isEnabled = "NO">
+         </CommandLineArgument>
+         <CommandLineArgument
+            argument = "--has-disk-drive"
+            isEnabled = "NO">
+         </CommandLineArgument>
         <CommandLineArgument
            argument = "&quot;/Users/thomasharte/Library/Mobile Documents/com~apple~CloudDocs/Desktop/Soft/Macintosh/MusicWorks 0.42.image&quot;"
            isEnabled = "NO">
@ -70,11 +82,11 @@
         </CommandLineArgument>
         <CommandLineArgument
            argument = "--volume=0.001"
-            isEnabled = "NO">
+            isEnabled = "YES">
         </CommandLineArgument>
         <CommandLineArgument
            argument = "--new=amstradcpc"
-            isEnabled = "YES">
+            isEnabled = "NO">
         </CommandLineArgument>
         <CommandLineArgument
            argument = "&quot;/Users/thomasharte/Library/Mobile Documents/com~apple~CloudDocs/Desktop/Soft/ColecoVision/Galaxian (1983)(Atari).col&quot;"
@ -116,6 +128,14 @@
            argument = "--model=cpc6128"
            isEnabled = "NO">
         </CommandLineArgument>
+         <CommandLineArgument
+            argument = "--new=appleii"
+            isEnabled = "NO">
+         </CommandLineArgument>
+         <CommandLineArgument
+            argument = "--use-square-pixels"
+            isEnabled = "YES">
+         </CommandLineArgument>
      </CommandLineArguments>
   </LaunchAction>
   <ProfileAction
--- a/Signal/Base.lproj/AppleIIOptions.xib
+++ b/Signal/Base.lproj/AppleIIOptions.xib
@ -1,8 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="14460.31" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
+<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="18122" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
    <dependencies>
        <deployment identifier="macosx"/>
-        <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="14460.31"/>
+        <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="18122"/>
        <capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>
    </dependencies>
    <objects>
@ -13,17 +13,27 @@
        </customObject>
        <customObject id="-1" userLabel="First Responder" customClass="FirstResponder"/>
        <customObject id="-3" userLabel="Application" customClass="NSObject"/>
-        <window title="Options" allowsToolTipsWhenApplicationIsInactive="NO" autorecalculatesKeyViewLoop="NO" hidesOnDeactivate="YES" releasedWhenClosed="NO" visibleAtLaunch="NO" frameAutosaveName="" animationBehavior="default" id="ZW7-Bw-4RP" customClass="MachinePanel" customModule="Clock_Signal" customModuleProvider="target">
+        <window title="Options" allowsToolTipsWhenApplicationIsInactive="NO" autorecalculatesKeyViewLoop="NO" hidesOnDeactivate="YES" releasedWhenClosed="NO" visibleAtLaunch="NO" frameAutosaveName="" animationBehavior="default" id="ZW7-Bw-4RP" customClass="AppleIIOptionsPanel" customModule="Clock_Signal" customModuleProvider="target">
            <windowStyleMask key="styleMask" titled="YES" closable="YES" utility="YES" nonactivatingPanel="YES" HUD="YES"/>
            <windowPositionMask key="initialPositionMask" leftStrut="YES" rightStrut="YES" topStrut="YES" bottomStrut="YES"/>
-            <rect key="contentRect" x="80" y="150" width="200" height="61"/>
-            <rect key="screenRect" x="0.0" y="0.0" width="1440" height="900"/>
+            <rect key="contentRect" x="80" y="150" width="200" height="159"/>
+            <rect key="screenRect" x="0.0" y="0.0" width="2560" height="1440"/>
            <view key="contentView" id="tpZ-0B-QQu">
-                <rect key="frame" x="0.0" y="0.0" width="200" height="61"/>
+                <rect key="frame" x="0.0" y="0.0" width="200" height="84"/>
                <autoresizingMask key="autoresizingMask"/>
                <subviews>
+                    <button verticalHuggingPriority="750" translatesAutoresizingMaskIntoConstraints="NO" id="kDb-7g-cVx">
+                        <rect key="frame" x="18" y="47" width="162" height="18"/>
+                        <buttonCell key="cell" type="check" title="Use Square Pixels" bezelStyle="regularSquare" imagePosition="left" state="on" inset="2" id="h9q-Wb-em8">
+                            <behavior key="behavior" changeContents="YES" doesNotDimImage="YES" lightByContents="YES"/>
+                            <font key="font" metaFont="system"/>
+                        </buttonCell>
+                        <connections>
+                            <action selector="optionDidChange:" target="ZW7-Bw-4RP" id="pNS-aK-0no"/>
+                        </connections>
+                    </button>
                    <popUpButton verticalHuggingPriority="750" translatesAutoresizingMaskIntoConstraints="NO" id="ex3-VM-58z">
-                        <rect key="frame" x="18" y="17" width="165" height="25"/>
+                        <rect key="frame" x="17" y="16" width="167" height="25"/>
                        <popUpButtonCell key="cell" type="push" title="Colour" bezelStyle="rounded" alignment="left" lineBreakMode="truncatingTail" state="on" borderStyle="borderAndBezel" tag="1" imageScaling="proportionallyDown" inset="2" selectedItem="gOu-dv-tre" id="u3N-Je-c2L">
                            <behavior key="behavior" lightByBackground="YES" lightByGray="YES"/>
                            <font key="font" metaFont="menu"/>
@ -40,16 +50,20 @@
                    </popUpButton>
                </subviews>
                <constraints>
-                    <constraint firstAttribute="bottom" secondItem="ex3-VM-58z" secondAttribute="bottom" constant="20" id="4ZS-q5-TJL"/>
+                    <constraint firstAttribute="bottom" secondItem="ex3-VM-58z" secondAttribute="bottom" constant="20" symbolic="YES" id="4ZS-q5-TJL"/>
                    <constraint firstItem="ex3-VM-58z" firstAttribute="leading" secondItem="tpZ-0B-QQu" secondAttribute="leading" constant="20" id="8Pj-Ns-TrJ"/>
+                    <constraint firstAttribute="trailing" secondItem="kDb-7g-cVx" secondAttribute="trailing" constant="20" symbolic="YES" id="KHa-of-eY7"/>
+                    <constraint firstItem="kDb-7g-cVx" firstAttribute="leading" secondItem="tpZ-0B-QQu" secondAttribute="leading" constant="20" symbolic="YES" id="OcZ-Xa-394"/>
                    <constraint firstAttribute="trailing" secondItem="ex3-VM-58z" secondAttribute="trailing" constant="20" id="QWA-lY-ugz"/>
-                    <constraint firstItem="ex3-VM-58z" firstAttribute="top" secondItem="tpZ-0B-QQu" secondAttribute="top" constant="20" id="szw-WO-3tS"/>
+                    <constraint firstItem="ex3-VM-58z" firstAttribute="top" secondItem="kDb-7g-cVx" secondAttribute="bottom" constant="8" id="jDW-N8-c4V"/>
+                    <constraint firstItem="kDb-7g-cVx" firstAttribute="top" secondItem="tpZ-0B-QQu" secondAttribute="top" constant="20" symbolic="YES" id="wdj-PF-zxO"/>
                </constraints>
            </view>
            <connections>
                <outlet property="displayTypeButton" destination="ex3-VM-58z" id="lmZ-aN-lcj"/>
+                <outlet property="squarePixelButton" destination="kDb-7g-cVx" id="zbx-o8-7yC"/>
            </connections>
-            <point key="canvasLocation" x="-161" y="38.5"/>
+            <point key="canvasLocation" x="-161" y="104.5"/>
        </window>
    </objects>
 </document>
--- a/Signal/Base.lproj/Atari2600Options.xib
+++ b/Signal/Base.lproj/Atari2600Options.xib
@ -1,8 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="14113" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
+<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="18122" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
    <dependencies>
        <deployment identifier="macosx"/>
-        <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="14113"/>
+        <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="18122"/>
        <capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>
    </dependencies>
    <objects>
@ -13,17 +13,17 @@
        </customObject>
        <customObject id="-1" userLabel="First Responder" customClass="FirstResponder"/>
        <customObject id="-3" userLabel="Application" customClass="NSObject"/>
-        <window title="Options" allowsToolTipsWhenApplicationIsInactive="NO" autorecalculatesKeyViewLoop="NO" hidesOnDeactivate="YES" oneShot="NO" releasedWhenClosed="NO" showsToolbarButton="NO" visibleAtLaunch="NO" frameAutosaveName="" animationBehavior="default" id="gsl-7V-TTU" customClass="Atari2600OptionsPanel" customModule="Clock_Signal" customModuleProvider="target">
+        <window title="Options" allowsToolTipsWhenApplicationIsInactive="NO" autorecalculatesKeyViewLoop="NO" hidesOnDeactivate="YES" releasedWhenClosed="NO" visibleAtLaunch="NO" frameAutosaveName="" animationBehavior="default" id="gsl-7V-TTU" customClass="Atari2600OptionsPanel" customModule="Clock_Signal" customModuleProvider="target">
            <windowStyleMask key="styleMask" titled="YES" closable="YES" utility="YES" nonactivatingPanel="YES" HUD="YES"/>
            <windowPositionMask key="initialPositionMask" leftStrut="YES" rightStrut="YES" topStrut="YES" bottomStrut="YES"/>
            <rect key="contentRect" x="80" y="150" width="200" height="121"/>
-            <rect key="screenRect" x="0.0" y="0.0" width="1440" height="900"/>
+            <rect key="screenRect" x="0.0" y="0.0" width="2560" height="1440"/>
            <view key="contentView" id="aQh-Pm-DEo">
                <rect key="frame" x="0.0" y="0.0" width="200" height="121"/>
                <autoresizingMask key="autoresizingMask"/>
                <subviews>
                    <button verticalHuggingPriority="750" translatesAutoresizingMaskIntoConstraints="NO" id="rQO-uD-fwn">
-                        <rect key="frame" x="14" y="73" width="86" height="32"/>
+                        <rect key="frame" x="13" y="74" width="88" height="32"/>
                        <buttonCell key="cell" type="push" title="Reset" bezelStyle="rounded" alignment="center" borderStyle="border" imageScaling="proportionallyDown" inset="2" id="l3H-0m-aK0">
                            <behavior key="behavior" pushIn="YES" lightByBackground="YES" lightByGray="YES"/>
                            <font key="font" metaFont="system"/>
@ -33,7 +33,7 @@
                        </connections>
                    </button>
                    <button translatesAutoresizingMaskIntoConstraints="NO" id="3qw-C1-NYW">
-                        <rect key="frame" x="18" y="58" width="164" height="18"/>
+                        <rect key="frame" x="18" y="58" width="162" height="18"/>
                        <buttonCell key="cell" type="check" title="Black and White" bezelStyle="regularSquare" imagePosition="left" inset="2" id="UP7-mf-IKo">
                            <behavior key="behavior" changeContents="YES" doesNotDimImage="YES" lightByContents="YES"/>
                            <font key="font" metaFont="system"/>
@ -43,7 +43,7 @@
                        </connections>
                    </button>
                    <button translatesAutoresizingMaskIntoConstraints="NO" id="Xbc-cw-Sc2">
-                        <rect key="frame" x="18" y="38" width="164" height="18"/>
+                        <rect key="frame" x="18" y="36" width="162" height="18"/>
                        <buttonCell key="cell" type="check" title="Left Player Difficulty" bezelStyle="regularSquare" imagePosition="left" inset="2" id="wlJ-8s-PEh">
                            <behavior key="behavior" changeContents="YES" doesNotDimImage="YES" lightByContents="YES"/>
                            <font key="font" metaFont="system"/>
@ -53,7 +53,7 @@
                        </connections>
                    </button>
                    <button translatesAutoresizingMaskIntoConstraints="NO" id="kPV-Tm-TTc">
-                        <rect key="frame" x="18" y="18" width="164" height="18"/>
+                        <rect key="frame" x="18" y="14" width="162" height="18"/>
                        <buttonCell key="cell" type="check" title="Right Player Difficulty" bezelStyle="regularSquare" imagePosition="left" inset="2" id="F05-cA-66S">
                            <behavior key="behavior" changeContents="YES" doesNotDimImage="YES" lightByContents="YES"/>
                            <font key="font" metaFont="system"/>
@ -63,7 +63,7 @@
                        </connections>
                    </button>
                    <button verticalHuggingPriority="750" translatesAutoresizingMaskIntoConstraints="NO" id="nt7-8K-xY9">
-                        <rect key="frame" x="100" y="73" width="86" height="32"/>
+                        <rect key="frame" x="99" y="74" width="88" height="32"/>
                        <buttonCell key="cell" type="push" title="Select" bezelStyle="rounded" alignment="center" borderStyle="border" imageScaling="proportionallyDown" inset="2" id="8Na-Z1-EXS">
                            <behavior key="behavior" pushIn="YES" lightByBackground="YES" lightByGray="YES"/>
                            <font key="font" metaFont="system"/>
--- a/Signal/Documents/MachineDocument.swift
+++ b/Signal/Documents/MachineDocument.swift
@ -137,22 +137,22 @@ class MachineDocument:
 		volumeSlider.floatValue = userDefaultsVolume()
 	}

-	private var missingROMs: [CSMissingROM] = []
+	private var missingROMs: String = ""
 	func configureAs(_ analysis: CSStaticAnalyser) {
 		self.machineDescription = analysis

 		actionLock.lock()
 		drawLock.lock()

-		let missingROMs = NSMutableArray()
+		let missingROMs = NSMutableString()
 		if let machine = CSMachine(analyser: analysis, missingROMs: missingROMs) {
+			setRomRequesterIsVisible(false)
+
 			self.machine = machine
 			machine.setVolume(userDefaultsVolume())
 			setupMachineOutput()
 		} else {
-			// Store the selected machine and list of missing ROMs, and
-			// show the missing ROMs dialogue.
-			self.missingROMs = missingROMs.map({$0 as! CSMissingROM})
+			self.missingROMs = missingROMs as String
 			requestRoms()
 		}

@ -413,23 +413,42 @@ class MachineDocument:
 	@IBOutlet var romReceiverErrorField: NSTextField?
 	@IBOutlet var romReceiverView: CSROMReceiverView?
 	private var romRequestBaseText = ""
+
+	private func setRomRequesterIsVisible(_ visible : Bool) {
+		if !visible && self.romRequesterPanel == nil {
+			return;
+		}
+
+		if self.romRequesterPanel!.isVisible == visible {
+			return
+		}
+
+		if visible {
+			self.windowControllers[0].window?.beginSheet(self.romRequesterPanel!, completionHandler: nil)
+		} else {
+			self.windowControllers[0].window?.endSheet(self.romRequesterPanel!)
+		}
+	}
+
 	func requestRoms() {
 		// Don't act yet if there's no window controller yet.
 		if self.windowControllers.count == 0 {
 			return
 		}

-		// Load the ROM requester dialogue.
-		Bundle.main.loadNibNamed("ROMRequester", owner: self, topLevelObjects: nil)
-		self.romReceiverView!.delegate = self
-		self.romRequestBaseText = romRequesterText!.stringValue
-		romReceiverErrorField?.alphaValue = 0.0
+		// Load the ROM requester dialogue if it's not already loaded.
+		if self.romRequesterPanel == nil {
+			Bundle.main.loadNibNamed("ROMRequester", owner: self, topLevelObjects: nil)
+			self.romReceiverView!.delegate = self
+			self.romRequestBaseText = romRequesterText!.stringValue
+			romReceiverErrorField?.alphaValue = 0.0
+		}

 		// Populate the current absentee list.
 		populateMissingRomList()

 		// Show the thing.
-		self.windowControllers[0].window?.beginSheet(self.romRequesterPanel!, completionHandler: nil)
+		setRomRequesterIsVisible(true)
 	}

 	@IBAction func cancelRequestROMs(_ sender: NSButton?) {
@ -437,89 +456,17 @@ class MachineDocument:
 	}

 	func populateMissingRomList() {
-		// Fill in the missing details; first build a list of all the individual
-		// line items.
-		var requestLines: [String] = []
-		for missingROM in self.missingROMs {
-			if let descriptiveName = missingROM.descriptiveName {
-				requestLines.append("• " + descriptiveName)
-			} else {
-				requestLines.append("• " + missingROM.fileName)
-			}
-		}
-
-		// Suffix everything up to the penultimate line with a semicolon;
-		// the penultimate line with a semicolon and a conjunctive; the final
-		// line with a full stop.
-		for x in 0 ..< requestLines.count {
-			if x < requestLines.count - 2 {
-				requestLines[x].append(";")
-			} else if x < requestLines.count - 1 {
-				requestLines[x].append("; and")
-			} else {
-				requestLines[x].append(".")
-			}
-		}
-		romRequesterText!.stringValue = self.romRequestBaseText + requestLines.joined(separator: "\n")
+		romRequesterText!.stringValue = self.romRequestBaseText + self.missingROMs
 	}

 	func romReceiverView(_ view: CSROMReceiverView, didReceiveFileAt URL: URL) {
 		// Test whether the file identified matches any of the currently missing ROMs.
 		// If so then remove that ROM from the missing list and update the request screen.
 		// If no ROMs are still missing, start the machine.
-		do {
-			let fileData = try Data(contentsOf: URL)
-			var didInstallRom = false
-
-			// Try to match by size first, CRC second. Accept that some ROMs may have
-			// some additional appended data. Arbitrarily allow them to be up to 10kb
-			// too large.
-			var index = 0
-			for missingROM in self.missingROMs {
-				if fileData.count >= missingROM.size && fileData.count < missingROM.size + 10*1024 {
-					// Trim to size.
-					let trimmedData = fileData[0 ..< missingROM.size]
-
-					// Get CRC.
-					if missingROM.crc32s.contains( (trimmedData as NSData).crc32 ) {
-						// This ROM matches; copy it into the application library,
-						// strike it from the missing ROM list and decide how to
-						// proceed.
-						let fileManager = FileManager.default
-						let targetPath = fileManager.urls(for: .applicationSupportDirectory, in: .userDomainMask)[0]
-							.appendingPathComponent("ROMImages")
-							.appendingPathComponent(missingROM.machineName)
-						let targetFile = targetPath
-							.appendingPathComponent(missingROM.fileName)
-
-						do {
-							try fileManager.createDirectory(atPath: targetPath.path, withIntermediateDirectories: true, attributes: nil)
-							try trimmedData.write(to: targetFile)
-						} catch let error {
-							showRomReceiverError(error: "Couldn't write to application support directory: \(error)")
-						}
-
-						self.missingROMs.remove(at: index)
-						didInstallRom = true
-						break
-					}
-				}
-
-				index = index + 1
-			}
-
-			if didInstallRom {
-				if self.missingROMs.count == 0 {
-					self.windowControllers[0].window?.endSheet(self.romRequesterPanel!)
-					configureAs(self.machineDescription!)
-				} else {
-					populateMissingRomList()
-				}
-			} else {
-				showRomReceiverError(error: "Didn't recognise contents of \(URL.lastPathComponent)")
-			}
-		} catch let error {
-			showRomReceiverError(error: "Couldn't read file at \(URL.absoluteString): \(error)")
+		if CSMachine.attemptInstallROM(URL) {
+			configureAs(self.machineDescription!)
+		} else {
+			showRomReceiverError(error: "Didn't recognise contents of \(URL.lastPathComponent)")
 		}
 	}

--- a/Signal/Machine/CSMachine.h
+++ b/Signal/Machine/CSMachine.h
@ -33,20 +33,15 @@ typedef NS_ENUM(NSInteger, CSMachineKeyboardInputMode) {
 	CSMachineKeyboardInputModeJoystick,
 };

-@interface CSMissingROM: NSObject
-@property (nonatomic, readonly, nonnull) NSString *machineName;
-@property (nonatomic, readonly, nonnull) NSString *fileName;
-@property (nonatomic, readonly, nullable) NSString *descriptiveName;
-@property (nonatomic, readonly) NSUInteger size;
-@property (nonatomic, readonly, nonnull) NSArray<NSNumber *> *crc32s;
-@end
-
 // Deliberately low; to ensure CSMachine has been declared as an @class already.
 #import "CSAtari2600.h"
 #import "CSZX8081.h"
+#import "CSAppleII.h"

@interface CSMachine : NSObject

+ (BOOL)attemptInstallROM:(nonnull NSURL *)url;
+
 - (nonnull instancetype)init NS_UNAVAILABLE;

 /*!
@ -56,7 +51,7 @@ typedef NS_ENUM(NSInteger, CSMachineKeyboardInputMode) {
 	@param missingROMs An array that is filled with a list of ROMs that the machine requested but which
 		were not found; populated only if this `init` has failed.
 */
- (nullable instancetype)initWithAnalyser:(nonnull CSStaticAnalyser *)result missingROMs:(nullable inout NSMutableArray<CSMissingROM *> *)missingROMs NS_DESIGNATED_INITIALIZER;
+- (nullable instancetype)initWithAnalyser:(nonnull CSStaticAnalyser *)result missingROMs:(nullable inout NSMutableString *)missingROMs NS_DESIGNATED_INITIALIZER;

 - (float)idealSamplingRateFromRange:(NSRange)range;
@property (readonly, getter=isStereo) BOOL stereo;
@ -109,5 +104,6 @@ typedef NS_ENUM(NSInteger, CSMachineKeyboardInputMode) {
 // Special-case accessors; undefined behaviour if accessed for a machine not of the corresponding type.
@property (nonatomic, readonly, nullable) CSAtari2600 *atari2600;
@property (nonatomic, readonly, nullable) CSZX8081 *zx8081;
+@property (nonatomic, readonly, nullable) CSAppleII *appleII;

@end
--- a/Signal/Machine/CSMachine.mm
+++ b/Signal/Machine/CSMachine.mm
@ -31,6 +31,8 @@

 #include <atomic>
 #include <bitset>
+#include <codecvt>
+#include <locale>

@interface CSMachine() <CSScanTargetViewDisplayLinkDelegate>
 - (void)speaker:(Outputs::Speaker::Speaker *)speaker didCompleteSamples:(const int16_t *)samples length:(int)length;
@ -74,28 +76,6 @@ struct ActivityObserver: public Activity::Observer {
 	__unsafe_unretained CSMachine *machine;
 };

-@interface CSMissingROM (/*Mutability*/)
-@property (nonatomic, nonnull, copy) NSString *machineName;
-@property (nonatomic, nonnull, copy) NSString *fileName;
-@property (nonatomic, nullable, copy) NSString *descriptiveName;
-@property (nonatomic, readwrite) NSUInteger size;
-@property (nonatomic, copy) NSArray<NSNumber *> *crc32s;
-@end
-
-@implementation CSMissingROM
-
-@synthesize machineName=_machineName;
-@synthesize fileName=_fileName;
-@synthesize descriptiveName=_descriptiveName;
-@synthesize size=_size;
-@synthesize crc32s=_crc32s;
-
- (NSString *)description {
-	return [NSString stringWithFormat:@"%@/%@, %lu bytes, CRCs: %@", _fileName, _descriptiveName, (unsigned long)_size, _crc32s];
-}
-
-@end
-
@implementation CSMachine {
 	SpeakerDelegate _speakerDelegate;
 	ActivityObserver _activityObserver;
@ -126,35 +106,18 @@ struct ActivityObserver: public Activity::Observer {
 	NSMutableArray<dispatch_block_t> *_inputEvents;
 }

- (instancetype)initWithAnalyser:(CSStaticAnalyser *)result missingROMs:(inout NSMutableArray<CSMissingROM *> *)missingROMs {
+- (instancetype)initWithAnalyser:(CSStaticAnalyser *)result missingROMs:(inout NSMutableString *)missingROMs {
 	self = [super init];
 	if(self) {
 		_analyser = result;

 		Machine::Error error;
-		std::vector<ROMMachine::ROM> missing_roms;
+		ROM::Request missing_roms;
 		_machine.reset(Machine::MachineForTargets(_analyser.targets, CSROMFetcher(&missing_roms), error));
 		if(!_machine) {
-			for(const auto &missing_rom : missing_roms) {
-				CSMissingROM *rom = [[CSMissingROM alloc] init];
-
-				// Copy/convert the primitive fields.
-				rom.machineName = @(missing_rom.machine_name.c_str());
-				rom.fileName = @(missing_rom.file_name.c_str());
-				rom.descriptiveName = missing_rom.descriptive_name.empty() ? nil : @(missing_rom.descriptive_name.c_str());
-				rom.size = missing_rom.size;
-
-				// Convert the CRC list.
-				NSMutableArray<NSNumber *> *crc32s = [[NSMutableArray alloc] initWithCapacity:missing_rom.crc32s.size()];
-				for(const auto &crc : missing_rom.crc32s) {
-					[crc32s addObject:@(crc)];
-				}
-				rom.crc32s = crc32s;
-
-				// Add to the missing list.
-				[missingROMs addObject:rom];
-			}
-
+			std::wstring_convert<std::codecvt_utf8<wchar_t>> wstring_converter;
+			const std::wstring description = missing_roms.description(0, L'•');
+			[missingROMs appendString:[NSString stringWithUTF8String:wstring_converter.to_bytes(description).c_str()]];
 			return nil;
 		}

@ -614,6 +577,10 @@ struct ActivityObserver: public Activity::Observer {
 	return [[CSZX8081 alloc] initWithZX8081:_machine->raw_pointer() owner:self];
 }

+- (CSAppleII *)appleII {
+	return [[CSAppleII alloc] initWithAppleII:_machine->raw_pointer() owner:self];
+}
+
 #pragma mark - Input device queries

 - (BOOL)hasJoystick {
@ -783,4 +750,8 @@ struct ActivityObserver: public Activity::Observer {
 	_timer = nil;
 }

+ (BOOL)attemptInstallROM:(NSURL *)url {
+	return CSInstallROM(url);
+}
+
@end
--- a/Signal/Machine/CSROMFetcher.hpp
+++ b/Signal/Machine/CSROMFetcher.hpp
@ -8,4 +8,5 @@

 #include "ROMMachine.hpp"

-ROMMachine::ROMFetcher CSROMFetcher(std::vector<ROMMachine::ROM> *missing_roms = nullptr);
+ROMMachine::ROMFetcher CSROMFetcher(ROM::Request *missing = nullptr);
+BOOL CSInstallROM(NSURL *);
--- a/Signal/Machine/CSROMFetcher.mm
+++ b/Signal/Machine/CSROMFetcher.mm
@ -11,47 +11,96 @@

 #import "NSBundle+DataResource.h"
 #import "NSData+StdVector.h"
+#import "NSData+CRC32.h"

 #include <string>

-ROMMachine::ROMFetcher CSROMFetcher(std::vector<ROMMachine::ROM> *missing_roms) {
-	return [missing_roms] (const std::vector<ROMMachine::ROM> &roms) -> std::vector<std::unique_ptr<std::vector<std::uint8_t>>> {
-		NSArray<NSURL *> *const supportURLs = [[NSFileManager defaultManager] URLsForDirectory:NSApplicationSupportDirectory inDomains:NSUserDomainMask];
+namespace {

-		std::vector<std::unique_ptr<std::vector<std::uint8_t>>> results;
-		for(const auto &rom: roms) {
-			NSData *fileData;
-			NSString *const subdirectory = [@"ROMImages/" stringByAppendingString:[NSString stringWithUTF8String:rom.machine_name.c_str()]];
+NSString *directoryFor(const ROM::Description &description) {
+	return [@"ROMImages/" stringByAppendingString:[NSString stringWithUTF8String:description.machine_name.c_str()]];
+}

-			// Check for this file first within the application support directories.
-			for(NSURL *supportURL in supportURLs) {
-				NSURL *const fullURL = [[supportURL URLByAppendingPathComponent:subdirectory]
-							URLByAppendingPathComponent:[NSString stringWithUTF8String:rom.file_name.c_str()]];
-				fileData = [NSData dataWithContentsOfURL:fullURL];
-				if(fileData) break;
+NSArray<NSURL *> *urlsFor(const ROM::Description &description, const std::string &file_name) {
+	NSMutableArray<NSURL *> *const urls = [[NSMutableArray alloc] init];
+	NSArray<NSURL *> *const supportURLs = [[NSFileManager defaultManager] URLsForDirectory:NSApplicationSupportDirectory inDomains:NSUserDomainMask];
+	NSString *const subdirectory = directoryFor(description);
+
+	for(NSURL *supportURL in supportURLs) {
+		[urls addObject:[[supportURL URLByAppendingPathComponent:subdirectory]
+								URLByAppendingPathComponent:[NSString stringWithUTF8String:file_name.c_str()]]];
+	}
+
+	return urls;
+}
+
+}
+
+BOOL CSInstallROM(NSURL *url) {
+	NSData *const data = [NSData dataWithContentsOfURL:url];
+	if(!data) return NO;
+
+	// Try for a direct CRC match.
+	std::optional<ROM::Description> target_description;
+	target_description = ROM::Description::from_crc(uint32_t(data.crc32.integerValue));
+
+	// See whether there's an acceptable trimming that creates a CRC match.
+	if(!target_description) {
+		const std::vector<ROM::Description> descriptions = ROM::all_descriptions();
+		for(const auto &description: descriptions) {
+			if(description.size > data.length) continue;
+
+			NSData *const trimmedData = [data subdataWithRange:NSMakeRange(0, description.size)];
+			if(description.crc32s.find(uint32_t(trimmedData.crc32.unsignedIntValue)) != description.crc32s.end()) {
+				target_description = description;
+				break;
 			}
+		}
+	}

-			// Failing that, check inside the application bundle.
-			if(!fileData) {
-				fileData = [[NSBundle mainBundle]
-					dataForResource:[NSString stringWithUTF8String:rom.file_name.c_str()]
-					withExtension:nil
-					subdirectory:subdirectory];
-			}
+	// If no destination was found, stop.
+	if(!target_description) {
+		return NO;
+	}

-			// Store an appropriate result, accumulating a list of the missing if requested.
-			if(!fileData) {
-				results.emplace_back(nullptr);
+	// Copy the data to its destination and report success.
+	NSURL *const targetURL = [urlsFor(*target_description, target_description->file_names[0]) firstObject];
+	[[NSFileManager defaultManager] createDirectoryAtPath:targetURL.URLByDeletingLastPathComponent.path withIntermediateDirectories:YES attributes:nil error:nil];
+	[data writeToURL:targetURL atomically:NO];

-				if(missing_roms) {
-					missing_roms->push_back(rom);
+	return YES;
+}
+
+ROMMachine::ROMFetcher CSROMFetcher(ROM::Request *missing) {
+	return [missing] (const ROM::Request &roms) -> ROM::Map {
+		ROM::Map results;
+		for(const auto &description: roms.all_descriptions()) {
+			for(const auto &file_name: description.file_names) {
+				NSData *fileData;
+
+				// Check for this file first within the application support directories.
+				for(NSURL *fileURL in urlsFor(description, file_name)) {
+					fileData = [NSData dataWithContentsOfURL:fileURL];
+					if(fileData) break;
+				}
+
+				// Failing that, check inside the application bundle.
+				if(!fileData) {
+					fileData = [[NSBundle mainBundle]
+						dataForResource:[NSString stringWithUTF8String:file_name.c_str()]
+						withExtension:nil
+						subdirectory:directoryFor(description)];
+				}
+
+				// Store an appropriate result.
+				if(fileData) {
+					results[description.name] = fileData.stdVector8;
 				}
 			}
-			else {
-				auto data = std::make_unique<std::vector<std::uint8_t>>();
-				*data = fileData.stdVector8;
-				results.emplace_back(std::move(data));
-			}
+		}
+
+		if(missing) {
+			*missing = roms.subtract(results);
 		}

 		return results;
--- a/Signal/Machine/Wrappers/CSAppleII.h
+++ b/Signal/Machine/Wrappers/CSAppleII.h
@ -0,0 +1,18 @@
+//
+//  CSAppleII.h
+//  Clock Signal
+//
+//  Created by Thomas Harte on 07/06/2021.
+//  Copyright © 2021 Thomas Harte. All rights reserved.
+//
+
+@class CSAppleII;
+#import "CSMachine.h"
+
+@interface CSAppleII : NSObject
+
+- (instancetype)initWithAppleII:(void *)appleII owner:(CSMachine *)machine;
+
+@property (nonatomic, assign) BOOL useSquarePixels;
+
+@end
--- a/Signal/Machine/Wrappers/CSAppleII.mm
+++ b/Signal/Machine/Wrappers/CSAppleII.mm
@ -0,0 +1,57 @@
+//
+//  CSAppleII.m
+//  Clock Signal
+//
+//  Created by Thomas Harte on 07/06/2021.
+//  Copyright © 2021 Thomas Harte. All rights reserved.
+//
+
+#import "CSAppleII.h"
+
+#include "AppleII.hpp"
+
+@implementation CSAppleII {
+	Apple::II::Machine *_appleII;
+	__weak CSMachine *_machine;
+}
+
+- (instancetype)initWithAppleII:(void *)appleII owner:(CSMachine *)machine {
+	self = [super init];
+	if(self) {
+		_appleII = (Apple::II::Machine *)appleII;
+		_machine = machine;
+	}
+	return self;
+}
+
+#pragma mark - Options
+
+- (void)setUseSquarePixels:(BOOL)useSquarePixels {
+	Configurable::Device *const configurable = dynamic_cast<Configurable::Device *>(_appleII);
+#ifndef NDEBUG
+	assert(configurable);
+#endif
+
+	@synchronized(_machine) {
+		auto options = configurable->get_options();
+#ifndef NDEBUG
+		assert(dynamic_cast<Apple::II::Machine::Options *>(options.get()));
+#endif
+
+		auto appleii_configurable = static_cast<Apple::II::Machine::Options *>(options.get());
+		appleii_configurable->use_square_pixels = useSquarePixels;
+		configurable->set_options(options);
+	}
+}
+
+- (BOOL)useSquarePixels {
+	Configurable::Device *const configurable = dynamic_cast<Configurable::Device *>(_appleII);
+
+	@synchronized(_machine) {
+		auto options = configurable->get_options();
+		auto appleii_configurable = dynamic_cast<Apple::II::Machine::Options *>(options.get());
+		return appleii_configurable->use_square_pixels ? YES : NO;
+	}
+}
+
+@end
--- a/Signal/ROMRequester/ROMRequester.xib
+++ b/Signal/ROMRequester/ROMRequester.xib
@ -1,8 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="17506" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
+<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="18122" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
    <dependencies>
        <deployment identifier="macosx"/>
-        <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="17506"/>
+        <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="18122"/>
        <capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>
    </dependencies>
    <objects>
@ -20,18 +20,16 @@
            <windowStyleMask key="styleMask" titled="YES"/>
            <windowPositionMask key="initialPositionMask" leftStrut="YES" rightStrut="YES" topStrut="YES" bottomStrut="YES"/>
            <rect key="contentRect" x="196" y="240" width="480" height="270"/>
-            <rect key="screenRect" x="0.0" y="0.0" width="1440" height="900"/>
+            <rect key="screenRect" x="0.0" y="0.0" width="2560" height="1440"/>
            <view key="contentView" wantsLayer="YES" id="EiT-Mj-1SZ" customClass="CSROMReceiverView">
                <rect key="frame" x="0.0" y="0.0" width="480" height="270"/>
                <autoresizingMask key="autoresizingMask"/>
                <subviews>
                    <textField verticalHuggingPriority="750" horizontalCompressionResistancePriority="250" setsMaxLayoutWidthAtFirstLayout="YES" textCompletion="NO" translatesAutoresizingMaskIntoConstraints="NO" id="5qG-I3-Qav">
-                        <rect key="frame" x="18" y="154" width="444" height="96"/>
+                        <rect key="frame" x="18" y="186" width="444" height="64"/>
                        <textFieldCell key="cell" enabled="NO" allowsUndo="NO" id="itJ-2T-0ia">
                            <font key="font" usesAppearanceFont="YES"/>
-                            <string key="title">Clock Signal requires you to provide images of the system ROMs for this machine. They will be stored permanently; you need do this only once.  Please drag and drop the following over this text:
-
-</string>
+                            <string key="title">Clock Signal requires you to provide images of the system ROMs for this machine. They will be stored permanently; you need do this only once.  Please drag and drop over this text</string>
                            <color key="textColor" name="labelColor" catalog="System" colorSpace="catalog"/>
                            <color key="backgroundColor" name="textBackgroundColor" catalog="System" colorSpace="catalog"/>
                        </textFieldCell>
--- a/SignalTests/Bridges/C1540Bridge.mm
+++ b/SignalTests/Bridges/C1540Bridge.mm
@ -35,7 +35,8 @@ class VanillaSerialPort: public Commodore::Serial::Port {
 		_serialPort = std::make_shared<VanillaSerialPort>();

 		auto rom_fetcher = CSROMFetcher();
-		_c1540 = std::make_unique<Commodore::C1540::Machine>(Commodore::C1540::Personality::C1540, rom_fetcher);
+		auto roms = rom_fetcher(Commodore::C1540::Machine::rom_request(Commodore::C1540::Personality::C1540));
+		_c1540 = std::make_unique<Commodore::C1540::Machine>(Commodore::C1540::Personality::C1540, roms);
 		_c1540->set_serial_bus(_serialBus);
 		Commodore::Serial::AttachPortAndBus(_serialPort, _serialBus);
 	}
--- a/SignalTests/EmuTOSTests.mm
+++ b/SignalTests/EmuTOSTests.mm
@ -103,21 +103,20 @@ class EmuTOS: public ComparativeBusHandler {
 	std::unique_ptr<EmuTOS> _machine;
 }

- (void)testImage:(NSString *)image trace:(NSString *)trace length:(int)length {
-	const std::vector<ROMMachine::ROM> rom_names = {{"AtariST", "", image.UTF8String, 0, 0 }};
-	const auto roms = CSROMFetcher()(rom_names);
+- (void)testImage:(ROM::Name)name trace:(NSString *)trace length:(int)length {
+	const auto roms = CSROMFetcher()(ROM::Request(name));
 	NSString *const traceLocation = [[NSBundle bundleForClass:[self class]] pathForResource:trace ofType:@"trace.txt.gz"];
-	_machine = std::make_unique<EmuTOS>(*roms[0], traceLocation.fileSystemRepresentation);
+	_machine = std::make_unique<EmuTOS>(roms.find(name)->second, traceLocation.fileSystemRepresentation);
 	_machine->run_for(HalfCycles(length));
 }

 - (void)testEmuTOSStartup {
-	[self testImage:@"etos192uk.img" trace:@"etos192uk" length:313490];
+	[self testImage:ROM::Name::AtariSTEmuTOS192 trace:@"etos192uk" length:313490];
 	// TODO: assert that machine is now STOPped.
 }

 - (void)testTOSStartup {
-	[self testImage:@"tos100.img" trace:@"tos100" length:54011091];
+	[self testImage:ROM::Name::AtariSTTOS100 trace:@"tos100" length:54011091];
 }

@end
--- a/SignalTests/QLTests.mm
+++ b/SignalTests/QLTests.mm
@ -101,10 +101,11 @@ class QL: public ComparativeBusHandler {
 	Tests the progression of Clock Signal's 68000 through the Sinclair QL's ROM against a known-good trace.
 */
 - (void)testStartup {
-	const std::vector<ROMMachine::ROM> rom_names = {{"SinclairQL", "", "js.rom", 0, 0 }};
-	const auto roms = CSROMFetcher()(rom_names);
+	constexpr ROM::Name rom_name = ROM::Name::SinclairQLJS;
+	ROM::Request request(rom_name);
+	const auto roms = CSROMFetcher()(request);
 	NSString *const traceLocation = [[NSBundle bundleForClass:[self class]] pathForResource:@"qltrace" ofType:@".txt.gz"];
-	_machine = std::make_unique<QL>(*roms[0], traceLocation.UTF8String);
+	_machine = std::make_unique<QL>(roms.find(rom_name)->second, traceLocation.UTF8String);

 	// This is how many cycles it takes to exhaust the supplied trace file.
 	_machine->run_for(HalfCycles(23923180));
--- a/SignalTests/SpectrumVideoContentionTests.mm
+++ b/SignalTests/SpectrumVideoContentionTests.mm
@ -24,8 +24,10 @@ struct ContentionAnalysis {
 	HalfCycles pattern[8];
 };

-template <Sinclair::ZXSpectrum::VideoTiming video_timing> ContentionAnalysis analyse() {
-	Sinclair::ZXSpectrum::Video<video_timing> video;
+using Timing = Sinclair::ZXSpectrum::Video::Timing;
+
+template <Timing video_timing> ContentionAnalysis analyse() {
+	Sinclair::ZXSpectrum::Video::Video<video_timing> video;
 	ContentionAnalysis analysis;

 	// Advance to the start of the first interrupt.
@ -82,7 +84,7 @@ template <Sinclair::ZXSpectrum::VideoTiming video_timing> ContentionAnalysis ana
 }

 - (void)test48k {
-	const auto analysis = analyse<Sinclair::ZXSpectrum::VideoTiming::FortyEightK>();
+	const auto analysis = analyse<Timing::FortyEightK>();

 	// Check time from interrupt.
 	XCTAssertEqual(analysis.time_after_interrupt, 14335*2);
@ -105,7 +107,7 @@ template <Sinclair::ZXSpectrum::VideoTiming video_timing> ContentionAnalysis ana
 }

 - (void)test128k {
-	const auto analysis = analyse<Sinclair::ZXSpectrum::VideoTiming::OneTwoEightK>();
+	const auto analysis = analyse<Timing::OneTwoEightK>();

 	// Check time from interrupt.
 	XCTAssertEqual(analysis.time_after_interrupt, 14361*2);
@ -128,7 +130,7 @@ template <Sinclair::ZXSpectrum::VideoTiming video_timing> ContentionAnalysis ana
 }

 - (void)testPlus3 {
-	const auto analysis = analyse<Sinclair::ZXSpectrum::VideoTiming::Plus3>();
+	const auto analysis = analyse<Timing::Plus3>();

 	// Check time from interrupt.
 	XCTAssertEqual(analysis.time_after_interrupt, 14361*2);
--- a/OSBindings/Qt/mainwindow.cpp
+++ b/OSBindings/Qt/mainwindow.cpp
@ -251,33 +251,33 @@ void MainWindow::tile(const QMainWindow *previous) {

 void MainWindow::launchMachine() {
 	const QStringList appDataLocations = QStandardPaths::standardLocations(QStandardPaths::AppDataLocation);
-	missingRoms.clear();

 	ROMMachine::ROMFetcher rom_fetcher = [&appDataLocations, this]
-		(const std::vector<ROMMachine::ROM> &roms) -> std::vector<std::unique_ptr<std::vector<uint8_t>>> {
-		std::vector<std::unique_ptr<std::vector<uint8_t>>> results;
+		(const ROM::Request &roms) -> ROM::Map {
+		ROM::Map results;

-		for(const auto &rom: roms) {
-			FILE *file = nullptr;
-			for(const auto &path: appDataLocations) {
-				const std::string source = path.toStdString() + "/ROMImages/" + rom.machine_name + "/" + rom.file_name;
-				const std::string nativeSource = QDir::toNativeSeparators(QString::fromStdString(source)).toStdString();
+		for(const auto &description: roms.all_descriptions()) {
+			for(const auto &file_name: description.file_names) {
+				FILE *file = nullptr;
+				for(const auto &path: appDataLocations) {
+					const std::string source = path.toStdString() + "/ROMImages/" + description.machine_name + "/" + file_name;
+					const std::string nativeSource = QDir::toNativeSeparators(QString::fromStdString(source)).toStdString();

-				file = fopen(nativeSource.c_str(), "rb");
-				if(file) break;
-			}
+					file = fopen(nativeSource.c_str(), "rb");
+					if(file) break;
+				}

-			if(file) {
-				auto data = fileContentsAndClose(file);
-				if(data) {
-					results.push_back(std::move(data));
-					continue;
+				if(file) {
+					auto data = fileContentsAndClose(file);
+					if(data) {
+						results[description.name] = *data;
+						continue;
+					}
 				}
 			}
-
-			results.push_back(nullptr);
-			missingRoms.push_back(rom);
 		}
+
+		missingRoms = roms.subtract(results);
 		return results;
 	};
 	Machine::Error error;
@ -291,22 +291,7 @@ void MainWindow::launchMachine() {

 				// Populate request text.
 				QString requestText = romRequestBaseText;
-				size_t index = 0;
-				for(const auto &rom: missingRoms) {
-					requestText += "• ";
-					requestText += rom.descriptive_name.c_str();
-
-					++index;
-					if(index == missingRoms.size()) {
-						requestText += ".\n";
-						continue;
-					}
-					if(index == missingRoms.size() - 1) {
-						requestText += "; and\n";
-						continue;
-					}
-					requestText += ";\n";
-				}
+				requestText += QString::fromWCharArray(missingRoms.description(0, L'•').c_str());
 				ui->missingROMsBox->setPlainText(requestText);
 			} break;
 		}
@ -418,7 +403,7 @@ void MainWindow::launchMachine() {
 		break;

 		case Analyser::Machine::AppleII:
-			addDisplayMenu(settingsPrefix, "Colour", "Monochrome", "", "");
+			addAppleIIMenu();
 		break;

 		case Analyser::Machine::Atari2600:
@ -686,6 +671,41 @@ void MainWindow::toggleAtari2600Switch(Atari2600Switch toggleSwitch) {
 	});
 }

+void MainWindow::addAppleIIMenu() {
+	// Add the standard display settings.
+	addDisplayMenu("appleII", "Colour", "Monochrome", "", "");
+
+	// Add an additional tick box, for square pixels.
+	QAction *const squarePixelsAction = new QAction(tr("Square Pixels"));
+	squarePixelsAction->setCheckable(true);
+	connect(squarePixelsAction, &QAction::triggered, this, [=] {
+		std::lock_guard lock_guard(machineMutex);
+
+		// Apply the new setting to the machine.
+		setAppleIISquarePixels(squarePixelsAction->isChecked());
+
+		// Also store it.
+		Settings settings;
+		settings.setValue("appleII.squarePixels", squarePixelsAction->isChecked());
+	});
+	displayMenu->addAction(squarePixelsAction);
+
+	// Establish initial selection.
+	Settings settings;
+	const bool useSquarePixels = settings.value("appleII.squarePixels").toBool();
+	squarePixelsAction->setChecked(useSquarePixels);
+	setAppleIISquarePixels(useSquarePixels);
+}
+
+void MainWindow::setAppleIISquarePixels(bool squarePixels) {
+	Configurable::Device *const configurable = machine->configurable_device();
+	auto options = configurable->get_options();
+	auto appleii_options = static_cast<Apple::II::Machine::Options *>(options.get());
+
+	appleii_options->use_square_pixels = squarePixels;
+	configurable->set_options(options);
+}
+
 void MainWindow::speaker_did_complete_samples(Outputs::Speaker::Speaker *, const std::vector<int16_t> &buffer) {
 	audioBuffer.write(buffer);
 }
@ -736,28 +756,23 @@ void MainWindow::dropEvent(QDropEvent* event) {
 				CRC::CRC32 generator;
 				const uint32_t crc = generator.compute_crc(*contents);

-				bool wasUsed = false;
-				for(const auto &rom: missingRoms) {
-					if(std::find(rom.crc32s.begin(), rom.crc32s.end(), crc) != rom.crc32s.end()) {
-						foundROM = true;
+				std::optional<ROM::Description> target_rom = ROM::Description::from_crc(crc);
+				if(target_rom) {
+					// Ensure the destination folder exists.
+					const std::string path = appDataLocation + "/ROMImages/" + target_rom->machine_name;
+					const QDir dir(QString::fromStdString(path));
+					if (!dir.exists())
+						dir.mkpath(".");

-						// Ensure the destination folder exists.
-						const std::string path = appDataLocation + "/ROMImages/" + rom.machine_name;
-						const QDir dir(QString::fromStdString(path));
-						if (!dir.exists())
-							dir.mkpath(".");
+					// Write into place.
+					const std::string destination =  QDir::toNativeSeparators(QString::fromStdString(path+ "/" + target_rom->file_names[0])).toStdString();
+					FILE *const target = fopen(destination.c_str(), "wb");
+					fwrite(contents->data(), 1, contents->size(), target);
+					fclose(target);

-						// Write into place.
-						const std::string destination =  QDir::toNativeSeparators(QString::fromStdString(path+ "/" + rom.file_name)).toStdString();
-						FILE *const target = fopen(destination.c_str(), "wb");
-						fwrite(contents->data(), 1, contents->size(), target);
-						fclose(target);
-
-						wasUsed = true;
-					}
-				}
-
-				if(!wasUsed) {
+					// Note that at least one meaningful ROM was supplied.
+					foundROM = true;
+				} else {
 					if(!unusedRoms.isEmpty()) unusedRoms += ", ";
 					unusedRoms += url.fileName();
 				}
--- a/OSBindings/Qt/mainwindow.h
+++ b/OSBindings/Qt/mainwindow.h
@ -20,8 +20,9 @@
 #include "../../Activity/Observer.hpp"

 // There are machine-specific controls for the following:
-#include "../../Machines/Sinclair/ZX8081/ZX8081.hpp"
+#include "../../Machines/Apple/AppleII/AppleII.hpp"
 #include "../../Machines/Atari/2600/Atari2600.hpp"
+#include "../../Machines/Sinclair/ZX8081/ZX8081.hpp"

 QT_BEGIN_NAMESPACE
 namespace Ui { class MainWindow; }
@ -60,7 +61,7 @@ class MainWindow : public QMainWindow, public Outputs::Speaker::Speaker::Delegat
 		void launchMachine();

 		QString romRequestBaseText;
-		std::vector<ROMMachine::ROM> missingRoms;
+		ROM::Request missingRoms;

 		// File drag and drop is supported.
 		void dragEnterEvent(QDragEnterEvent* event) override;
@ -137,6 +138,9 @@ class MainWindow : public QMainWindow, public Outputs::Speaker::Speaker::Delegat
 		void addAtari2600Menu();
 		void toggleAtari2600Switch(Atari2600Switch toggleSwitch);

+		void addAppleIIMenu();
+		void setAppleIISquarePixels(bool);
+
 		void setWindowTitle();
 		bool mouseIsCaptured = false;

--- a/OSBindings/Qt/mainwindow.ui
+++ b/OSBindings/Qt/mainwindow.ui
@ -860,9 +860,7 @@
      <property name="plainText">
       <string>Clock Signal requires you to provide images of the system ROMs for this machine. They will be stored permanently; you need do this only once.

-Please drag and drop the following over this window:
-
-</string>
+Please drag and drop over this window</string>
      </property>
     </widget>
    </item>
--- a/OSBindings/SDL/main.cpp
+++ b/OSBindings/SDL/main.cpp
@ -694,11 +694,10 @@ int main(int argc, char *argv[]) {
 	//	/usr/local/share/CLK/[system];
 	//	/usr/share/CLK/[system]; or
 	//	[user-supplied path]/[system]
-	std::vector<ROMMachine::ROM> requested_roms;
-	ROMMachine::ROMFetcher rom_fetcher = [&requested_roms, &arguments]
-		(const std::vector<ROMMachine::ROM> &roms) -> std::vector<std::unique_ptr<std::vector<uint8_t>>> {
-			requested_roms.insert(requested_roms.end(), roms.begin(), roms.end());
-
+	ROM::Request missing_roms;
+	std::vector<std::string> checked_paths;
+	ROMMachine::ROMFetcher rom_fetcher = [&missing_roms, &arguments, &checked_paths]
+		(const ROM::Request &roms) -> ROM::Map {
 			std::vector<std::string> paths = {
 				"/usr/local/share/CLK/",
 				"/usr/share/CLK/"
@ -706,41 +705,56 @@ int main(int argc, char *argv[]) {

 			const auto rompath = arguments.selections.find("rompath");
 			if(rompath != arguments.selections.end()) {
-				if(rompath->second.back() != '/') {
-					paths.push_back(rompath->second + "/");
-				} else {
-					paths.push_back(rompath->second);
+				std::string path = rompath->second;
+
+				// Ensure the path ends in a slash.
+				if(path.back() != '/') {
+					path += '/';
+				}
+
+				// If ~ is present, expand it to %HOME%.
+				const size_t tilde_position = path.find("~");
+				if(tilde_position != std::string::npos) {
+					path.replace(tilde_position, 1, getenv("HOME"));
+				}
+
+				paths.push_back(path);
+			}
+
+			ROM::Map results;
+			for(const auto &description: roms.all_descriptions()) {
+				for(const auto &file_name: description.file_names) {
+					FILE *file = nullptr;
+					std::vector<std::string> rom_checked_paths;
+					for(const auto &path: paths) {
+						std::string local_path = path + description.machine_name + "/" + file_name;
+						file = std::fopen(local_path.c_str(), "rb");
+						rom_checked_paths.push_back(local_path);
+						if(file) break;
+					}
+
+					if(!file) {
+						std::copy(rom_checked_paths.begin(), rom_checked_paths.end(), std::back_inserter(checked_paths));
+						continue;
+					}
+
+					std::vector<uint8_t> data;
+
+					std::fseek(file, 0, SEEK_END);
+					data.resize(std::ftell(file));
+					std::fseek(file, 0, SEEK_SET);
+					std::size_t read = fread(data.data(), 1, data.size(), file);
+					std::fclose(file);
+
+					if(read == data.size()) {
+						results[description.name] = std::move(data);
+					} else {
+						std::copy(rom_checked_paths.begin(), rom_checked_paths.end(), std::back_inserter(checked_paths));
+					}
 				}
 			}

-			std::vector<std::unique_ptr<std::vector<uint8_t>>> results;
-			for(const auto &rom: roms) {
-				FILE *file = nullptr;
-				for(const auto &path: paths) {
-					std::string local_path = path + rom.machine_name + "/" + rom.file_name;
-					file = std::fopen(local_path.c_str(), "rb");
-					if(file) break;
-				}
-
-				if(!file) {
-					results.emplace_back(nullptr);
-					continue;
-				}
-
-				auto data = std::make_unique<std::vector<uint8_t>>();
-
-				std::fseek(file, 0, SEEK_END);
-				data->resize(std::ftell(file));
-				std::fseek(file, 0, SEEK_SET);
-				std::size_t read = fread(data->data(), 1, data->size(), file);
-				std::fclose(file);
-
-				if(read == data->size())
-					results.emplace_back(std::move(data));
-				else
-					results.emplace_back(nullptr);
-			}
-
+			missing_roms = roms.subtract(results);
 			return results;
 		};

@ -758,24 +772,22 @@ int main(int argc, char *argv[]) {
 	if(!machine) {
 		switch(error) {
 			default: break;
-			case ::Machine::Error::MissingROM:
-				std::cerr << "Could not find system ROMs; please install to /usr/local/share/CLK/ or /usr/share/CLK/, or provide a --rompath." << std::endl;
-				std::cerr << "One or more of the following was needed but not found:" << std::endl;
-				for(const auto &rom: requested_roms) {
-					std::cerr << rom.machine_name << '/' << rom.file_name << " (";
-					if(!rom.descriptive_name.empty()) {
-						std::cerr << rom.descriptive_name << "; ";
-					}
-					std::cerr << "usual crc32s: ";
-					bool is_first = true;
-					for(const auto crc32: rom.crc32s) {
-						if(!is_first) std::cerr << ", ";
-						is_first = false;
-						std::cerr << std::hex << std::setfill('0') << std::setw(8) << crc32;
-					}
-					std::cerr << ")" << std::endl;
+			case ::Machine::Error::MissingROM: {
+				std::cerr << "Could not find system ROMs; please install to /usr/local/share/CLK/ or /usr/share/CLK/, or provide a --rompath, e.g. --rompath=~/ROMs." << std::endl;
+				std::cerr << "Needed — but didn't find —";
+
+				using DescriptionFlag = ROM::Description::DescriptionFlag;
+				std::wcerr << missing_roms.description(DescriptionFlag::Filename | DescriptionFlag::CRC, L'*');
+
+				std::cerr << std::endl << std::endl << "Searched unsuccessfully: ";
+				bool is_first = true;
+				for(const auto &path: checked_paths) {
+					if(!is_first) std::cerr << "; ";
+					std::cerr << path;
+					is_first = false;
 				}
-			break;
+				std::cerr << std::endl;
+			} break;
 		}

 		return EXIT_FAILURE;