diff --git a/Analyser/Static/Acorn/StaticAnalyser.cpp b/Analyser/Static/Acorn/StaticAnalyser.cpp
index 76d655cfc..d5a34167b 100644
--- a/Analyser/Static/Acorn/StaticAnalyser.cpp
+++ b/Analyser/Static/Acorn/StaticAnalyser.cpp
@@ -61,10 +61,6 @@ static std::vector<std::shared_ptr<Storage::Cartridge::Cartridge>>
 
 Analyser::Static::TargetList Analyser::Static::Acorn::GetTargets(const Media &media, const std::string &, TargetPlatform::IntType) {
 	auto target = std::make_unique<Target>();
-	target->confidence = 0.5; // TODO: a proper estimation
-	target->has_dfs = false;
-	target->has_adfs = false;
-	target->should_shift_restart = false;
 
 	// strip out inappropriate cartridges
 	target->media.cartridges = AcornCartridgesFrom(media.cartridges);
@@ -111,9 +107,10 @@ Analyser::Static::TargetList Analyser::Static::Acorn::GetTargets(const Media &me
 		if(dfs_catalogue == nullptr) adfs_catalogue = GetADFSCatalogue(disk);
 		if(dfs_catalogue || adfs_catalogue) {
 			// Accept the disk and determine whether DFS or ADFS ROMs are implied.
+			// Use the Pres ADFS if using an ADFS, as it leaves Page at &EOO.
 			target->media.disks = media.disks;
 			target->has_dfs = bool(dfs_catalogue);
-			target->has_adfs = bool(adfs_catalogue);
+			target->has_pres_adfs = bool(adfs_catalogue);
 
 			// Check whether a simple shift+break will do for loading this disk.
 			Catalogue::BootOption bootOption = (dfs_catalogue ?: adfs_catalogue)->bootOption;
@@ -144,6 +141,28 @@ Analyser::Static::TargetList Analyser::Static::Acorn::GetTargets(const Media &me
 		}
 	}
 
+	// Enable the Acorn ADFS if a mass-storage device is attached;
+	// unlike the Pres ADFS it retains SCSI logic.
+	if(!media.mass_storage_devices.empty()) {
+		target->has_pres_adfs = false;	// To override a floppy selection, if one was made.
+		target->has_acorn_adfs = true;
+
+		// Assume some sort of later-era Acorn work is likely to happen;
+		// so ensure *TYPE, etc are present.
+		target->has_ap6_rom = true;
+		target->has_sideways_ram = true;
+
+		target->media.mass_storage_devices = media.mass_storage_devices;
+
+		// Check for a boot option.
+		const auto sector = target->media.mass_storage_devices.front()->get_block(1);
+		if(sector[0xfd]) {
+			target->should_shift_restart = true;
+		} else {
+			target->loading_command = "*CAT\n";
+		}
+	}
+
 	TargetList targets;
 	if(!target->media.empty()) {
 		targets.push_back(std::move(target));
diff --git a/Analyser/Static/Acorn/Target.hpp b/Analyser/Static/Acorn/Target.hpp
index f415f4b30..17dad7393 100644
--- a/Analyser/Static/Acorn/Target.hpp
+++ b/Analyser/Static/Acorn/Target.hpp
@@ -18,7 +18,8 @@ namespace Static {
 namespace Acorn {
 
 struct Target: public ::Analyser::Static::Target, public Reflection::StructImpl<Target> {
-	bool has_adfs = false;
+	bool has_acorn_adfs = false;
+	bool has_pres_adfs = false;
 	bool has_dfs = false;
 	bool has_ap6_rom = false;
 	bool has_sideways_ram = false;
@@ -27,7 +28,8 @@ struct Target: public ::Analyser::Static::Target, public Reflection::StructImpl<
 
 	Target() : Analyser::Static::Target(Machine::Electron) {
 		if(needs_declare()) {
-			DeclareField(has_adfs);
+			DeclareField(has_pres_adfs);
+			DeclareField(has_acorn_adfs);
 			DeclareField(has_dfs);
 			DeclareField(has_ap6_rom);
 			DeclareField(has_sideways_ram);
diff --git a/Analyser/Static/StaticAnalyser.cpp b/Analyser/Static/StaticAnalyser.cpp
index ad80cd8fb..57fc02a45 100644
--- a/Analyser/Static/StaticAnalyser.cpp
+++ b/Analyser/Static/StaticAnalyser.cpp
@@ -51,6 +51,7 @@
 #include "../../Storage/Disk/DiskImage/Formats/WOZ.hpp"
 
 // Mass Storage Devices (i.e. usually, hard disks)
+#include "../../Storage/MassStorage/Formats/DAT.hpp"
 #include "../../Storage/MassStorage/Formats/HFV.hpp"
 
 // Tapes
@@ -105,6 +106,7 @@ static Media GetMediaAndPlatforms(const std::string &file_name, TargetPlatform::
 	Format("col", result.cartridges, Cartridge::BinaryDump, TargetPlatform::ColecoVision)						// COL
 	Format("csw", result.tapes, Tape::CSW, TargetPlatform::AllTape)												// CSW
 	Format("d64", result.disks, Disk::DiskImageHolder<Storage::Disk::D64>, TargetPlatform::Commodore)			// D64
+	Format("dat", result.mass_storage_devices, MassStorage::DAT, TargetPlatform::Acorn)							// DAT
 	Format("dmk", result.disks, Disk::DiskImageHolder<Storage::Disk::DMK>, TargetPlatform::MSX)					// DMK
 	Format("do", result.disks, Disk::DiskImageHolder<Storage::Disk::AppleDSK>, TargetPlatform::DiskII)			// DO
 	Format("dsd", result.disks, Disk::DiskImageHolder<Storage::Disk::SSD>, TargetPlatform::Acorn)				// DSD
diff --git a/Machines/Electron/Electron.cpp b/Machines/Electron/Electron.cpp
index 4344e44a4..076547ff1 100644
--- a/Machines/Electron/Electron.cpp
+++ b/Machines/Electron/Electron.cpp
@@ -17,6 +17,9 @@
 #include "../../Configurable/StandardOptions.hpp"
 #include "../../Outputs/Speaker/Implementation/LowpassSpeaker.hpp"
 #include "../../Processors/6502/6502.hpp"
+
+#include "../../Storage/MassStorage/SCSI/SCSI.hpp"
+#include "../../Storage/MassStorage/SCSI/DirectAccessDevice.hpp"
 #include "../../Storage/Tape/Tape.hpp"
 
 #include "../Utility/Typer.hpp"
@@ -31,7 +34,7 @@
 
 namespace Electron {
 
-class ConcreteMachine:
+template <bool has_scsi_bus> class ConcreteMachine:
 	public Machine,
 	public MachineTypes::TimedMachine,
 	public MachineTypes::ScanProducer,
@@ -42,10 +45,15 @@ class ConcreteMachine:
 	public CPU::MOS6502::BusHandler,
 	public Tape::Delegate,
 	public Utility::TypeRecipient<CharacterMapper>,
-	public Activity::Source {
+	public Activity::Source,
+	public SCSI::Bus::Observer,
+	public ClockingHint::Observer {
 	public:
 		ConcreteMachine(const Analyser::Static::Acorn::Target &target, const ROMMachine::ROMFetcher &rom_fetcher) :
 				m6502_(*this),
+				scsi_bus_(4'000'000),
+				hard_drive_(scsi_bus_, 0),
+				scsi_device_(scsi_bus_.add_device()),
 				video_output_(ram_),
 				sound_generator_(audio_queue_),
 				speaker_(sound_generator_) {
@@ -64,10 +72,15 @@ class ConcreteMachine:
 				{machine_name, "the Acorn BASIC II ROM", "basic.rom", 16*1024, 0x79434781},
 				{machine_name, "the Electron MOS ROM", "os.rom", 16*1024, 0xbf63fb1f}
 			};
-			if(target.has_adfs) {
+			const size_t pres_adfs_rom_position = required_roms.size();
+			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);
 			}
+			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);
+			}
 			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);
@@ -91,19 +104,23 @@ class ConcreteMachine:
 
 					* the keyboard and BASIC ROMs occupy slots 8, 9, 10 and 11;
 					* the DFS, if in use, occupies slot 1;
-					* the ADFS, if in use, occupies slots 4 and 5;
+					* the Pres ADFS, if in use, occupies slots 4 and 5;
+					* the Acorn ADFS, if in use, occupies slot 6;
 					* the AP6, if in use, occupies slot 15; and
 					* if sideways RAM was asked for, all otherwise unused slots are populated with sideways RAM.
 			*/
-			if(target.has_dfs || target.has_adfs) {
+			if(target.has_dfs || target.has_acorn_adfs || target.has_pres_adfs) {
 				plus3_ = std::make_unique<Plus3>();
 
 				if(target.has_dfs) {
 					set_rom(ROM::Slot0, *roms[dfs_rom_position], true);
 				}
-				if(target.has_adfs) {
-					set_rom(ROM::Slot4, *roms[2], true);
-					set_rom(ROM::Slot5, *roms[3], 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);
+				}
+				if(target.has_acorn_adfs) {
+					set_rom(ROM::Slot6, *roms[acorn_adfs_rom_position], true);
 				}
 			}
 
@@ -128,6 +145,11 @@ class ConcreteMachine:
 			if(target.should_shift_restart) {
 				shift_restart_counter_ = 1000000;
 			}
+
+			if(has_scsi_bus) {
+				scsi_bus_.add_observer(this);
+				scsi_bus_.set_clocking_hint_observer(this);
+			}
 		}
 
 		~ConcreteMachine() {
@@ -193,7 +215,12 @@ class ConcreteMachine:
 				set_rom(slot, cartridge->get_segments().front().data, false);
 			}
 
-			return !media.tapes.empty() || !media.disks.empty() || !media.cartridges.empty();
+			// TODO: allow this only at machine startup?
+			if(!media.mass_storage_devices.empty()) {
+				hard_drive_->set_storage(media.mass_storage_devices.front());
+			}
+
+			return !media.empty();
 		}
 
 		forceinline Cycles perform_bus_operation(CPU::MOS6502::BusOperation operation, uint16_t address, uint8_t *value) {
@@ -315,7 +342,73 @@ class ConcreteMachine:
 								plus3_->set_control_register(*value);
 							} else *value = 1;
 						}
+
+						if(has_scsi_bus && (address&0x00f0) == 0x0040) {
+							scsi_acknowledge_ = true;
+							if(!isReadOperation(operation)) {
+								scsi_data_ = *value;
+								push_scsi_output();
+							} else {
+								*value = SCSI::data_lines(scsi_bus_.get_state());
+								push_scsi_output();
+							}
+						}
 					break;
+					case 0xfc03:
+						if(has_scsi_bus && (address&0x00f0) == 0x0040) {
+							scsi_interrupt_state_ = false;
+							scsi_interrupt_mask_ = *value & 1;
+							evaluate_interrupts();
+						}
+					break;
+					case 0xfc01:
+						if(has_scsi_bus && (address&0x00f0) == 0x0040 && isReadOperation(operation)) {
+							// Status byte is:
+							//
+							//	b7:	SCSI C/D
+							//	b6: SCSI I/O
+							//	b5: SCSI REQ
+							//	b4: interrupt flag
+							//	b3:	0
+							//	b2:	0
+							//	b1:	SCSI BSY
+							//	b0: SCSI MSG
+							const auto state = scsi_bus_.get_state();
+							*value =
+								(state & SCSI::Line::Control ? 0x80 : 0x00) |
+								(state & SCSI::Line::Input ? 0x40 : 0x00) |
+								(state & SCSI::Line::Request ? 0x20 : 0x00) |
+								((scsi_interrupt_state_ && scsi_interrupt_mask_) ? 0x10 : 0x00) |
+								(state & SCSI::Line::Busy ? 0x02 : 0x00) |
+								(state & SCSI::Line::Message ? 0x01 : 0x00);
+
+							// Empirical guess: this is also the trigger to affect busy/request/acknowledge
+							// signalling. Maybe?
+							if(scsi_select_ && scsi_bus_.get_state() & SCSI::Line::Busy) {
+								scsi_select_ = false;
+								push_scsi_output();
+							}
+						}
+					break;
+					case 0xfc02:
+						if(has_scsi_bus && (address&0x00f0) == 0x0040) {
+							scsi_select_ = true;
+							push_scsi_output();
+						}
+					break;
+
+					// SCSI locations:
+					//
+					//	fc40:	data, read and write
+					//	fc41:	status read
+					//	fc42:	select write
+					//	fc43:	interrupt latch
+					//
+					//
+					// Interrupt latch is:
+					//
+					//	b0: enable or disable IRQ on REQ
+					//	(and, possibly, writing to the latch acknowledges?)
 
 					default:
 						if(address >= 0xc000) {
@@ -414,6 +507,12 @@ class ConcreteMachine:
 				}
 			}
 
+			if constexpr (has_scsi_bus) {
+				if(scsi_is_clocked_) {
+					scsi_bus_.run_for(Cycles(int(cycles)));
+				}
+			}
+
 			return Cycles(int(cycles));
 		}
 
@@ -447,6 +546,28 @@ class ConcreteMachine:
 			m6502_.run_for(cycles);
 		}
 
+		void scsi_bus_did_change(SCSI::Bus *, SCSI::BusState new_state, double) final {
+			// Release acknowledge when request is released.
+			if(scsi_acknowledge_ && !(new_state & SCSI::Line::Request)) {
+				scsi_acknowledge_ = false;
+				push_scsi_output();
+			}
+
+			// Output occurs only while SCSI::Line::Input is inactive; therefore a change
+			// in that line affects what's on the bus.
+			if(((new_state^previous_bus_state_)&SCSI::Line::Input)) {
+				push_scsi_output();
+			}
+
+			scsi_interrupt_state_ |= (new_state^previous_bus_state_)&new_state & SCSI::Line::Request;
+			previous_bus_state_ = new_state;
+			evaluate_interrupts();
+		}
+
+		void set_component_prefers_clocking(ClockingHint::Source *, ClockingHint::Preference preference) final {
+			scsi_is_clocked_ = preference != ClockingHint::Preference::None;
+		}
+
 		void tape_did_change_interrupt_status(Tape *) final {
 			interrupt_status_ = (interrupt_status_ & ~(Interrupt::TransmitDataEmpty | Interrupt::ReceiveDataFull | Interrupt::HighToneDetect)) | tape_.get_interrupt_status();
 			evaluate_interrupts();
@@ -503,10 +624,14 @@ class ConcreteMachine:
 			if(activity_observer_) {
 				activity_observer_->register_led(caps_led);
 				activity_observer_->set_led_status(caps_led, caps_led_state_);
+			}
 
-				if(plus3_) {
-					plus3_->set_activity_observer(observer);
-				}
+			if(plus3_) {
+				plus3_->set_activity_observer(observer);
+			}
+
+			if(has_scsi_bus) {
+				scsi_bus_.set_activity_observer(observer);
 			}
 		}
 
@@ -600,7 +725,12 @@ class ConcreteMachine:
 			} else {
 				interrupt_status_ &= ~1;
 			}
-			m6502_.set_irq_line(interrupt_status_ & 1);
+
+			if constexpr (has_scsi_bus) {
+				m6502_.set_irq_line((scsi_interrupt_state_ && scsi_interrupt_mask_) | (interrupt_status_ & 1));
+			} else {
+				m6502_.set_irq_line(interrupt_status_ & 1);
+			}
 		}
 
 		CPU::MOS6502::Processor<CPU::MOS6502::Personality::P6502, ConcreteMachine, false> m6502_;
@@ -644,6 +774,25 @@ class ConcreteMachine:
 		bool is_holding_shift_ = false;
 		int shift_restart_counter_ = 0;
 
+		// Hard drive.
+		SCSI::Bus scsi_bus_;
+		SCSI::Target::Target<SCSI::DirectAccessDevice> hard_drive_;
+		SCSI::BusState previous_bus_state_ = SCSI::DefaultBusState;
+		const size_t scsi_device_ = 0;
+		uint8_t scsi_data_ = 0;
+		bool scsi_select_ = false;
+		bool scsi_acknowledge_ = false;
+		bool scsi_is_clocked_ = false;
+		bool scsi_interrupt_state_ = false;
+		bool scsi_interrupt_mask_ = false;
+		void push_scsi_output() {
+			scsi_bus_.set_device_output(scsi_device_,
+				(scsi_bus_.get_state()&SCSI::Line::Input ? 0 : scsi_data_) |
+				(scsi_select_ ? SCSI::Line::SelectTarget : 0) |
+				(scsi_acknowledge_ ? SCSI::Line::Acknowledge : 0)
+			);
+		}
+
 		// Outputs
 		VideoOutput video_output_;
 
@@ -666,7 +815,12 @@ using namespace Electron;
 Machine *Machine::Electron(const Analyser::Static::Target *target, const ROMMachine::ROMFetcher &rom_fetcher) {
 	using Target = Analyser::Static::Acorn::Target;
 	const Target *const acorn_target = dynamic_cast<const Target *>(target);
-	return new Electron::ConcreteMachine(*acorn_target, rom_fetcher);
+
+	if(acorn_target->media.mass_storage_devices.empty()) {
+		return new Electron::ConcreteMachine<false>(*acorn_target, rom_fetcher);
+	} else {
+		return new Electron::ConcreteMachine<true>(*acorn_target, rom_fetcher);
+	}
 }
 
 Machine::~Machine() {}
diff --git a/Machines/Electron/Keyboard.cpp b/Machines/Electron/Keyboard.cpp
index 887ac5aff..c554c2cbe 100644
--- a/Machines/Electron/Keyboard.cpp
+++ b/Machines/Electron/Keyboard.cpp
@@ -16,6 +16,7 @@ uint16_t KeyboardMapper::mapped_key_for_key(Inputs::Keyboard::Key key) const {
 		default: break;
 
 		BIND(BackTick, KeyCopy);
+		BIND(Backslash, KeyCopy);
 
 		BIND(k0, Key0);		BIND(k1, Key1);		BIND(k2, Key2);		BIND(k3, Key3);		BIND(k4, Key4);
 		BIND(k5, Key5);		BIND(k6, Key6);		BIND(k7, Key7);		BIND(k8, Key8);		BIND(k9, Key9);
diff --git a/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj b/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj
index 92ace4adc..d33f3f630 100644
--- a/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj	
+++ b/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj	
@@ -850,6 +850,7 @@
 		4BE211DE253E4E4800435408 /* 65C02_no_Rockwell_test.bin in Resources */ = {isa = PBXBuildFile; fileRef = 4BE211DD253E4E4800435408 /* 65C02_no_Rockwell_test.bin */; };
 		4BE34438238389E10058E78F /* AtariSTVideoTests.mm in Sources */ = {isa = PBXBuildFile; fileRef = 4BE34437238389E10058E78F /* AtariSTVideoTests.mm */; };
 		4BE76CF922641ED400ACD6FA /* QLTests.mm in Sources */ = {isa = PBXBuildFile; fileRef = 4BE76CF822641ED300ACD6FA /* QLTests.mm */; };
+		4BE8EB6625C750B50040BC40 /* DAT.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BE8EB6425C750B50040BC40 /* DAT.cpp */; };
 		4BE90FFD22D5864800FB464D /* MacintoshVideoTests.mm in Sources */ = {isa = PBXBuildFile; fileRef = 4BE90FFC22D5864800FB464D /* MacintoshVideoTests.mm */; };
 		4BE9A6B11EDE293000CBCB47 /* zexdoc.com in Resources */ = {isa = PBXBuildFile; fileRef = 4BE9A6B01EDE293000CBCB47 /* zexdoc.com */; };
 		4BEA525E1DF33323007E74F2 /* Tape.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BEA525D1DF33323007E74F2 /* Tape.cpp */; };
@@ -1788,6 +1789,8 @@
 		4BE34437238389E10058E78F /* AtariSTVideoTests.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = AtariSTVideoTests.mm; sourceTree = "<group>"; };
 		4BE76CF822641ED300ACD6FA /* QLTests.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = QLTests.mm; sourceTree = "<group>"; };
 		4BE845201F2FF7F100A5EA22 /* CRTC6845.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; name = CRTC6845.hpp; path = 6845/CRTC6845.hpp; sourceTree = "<group>"; };
+		4BE8EB6425C750B50040BC40 /* DAT.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = DAT.cpp; sourceTree = "<group>"; };
+		4BE8EB6525C750B50040BC40 /* DAT.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = DAT.hpp; sourceTree = "<group>"; };
 		4BE90FFC22D5864800FB464D /* MacintoshVideoTests.mm */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.objcpp; path = MacintoshVideoTests.mm; sourceTree = "<group>"; };
 		4BE9A6B01EDE293000CBCB47 /* zexdoc.com */ = {isa = PBXFileReference; lastKnownFileType = file; name = zexdoc.com; path = Zexall/zexdoc.com; sourceTree = "<group>"; };
 		4BEA525D1DF33323007E74F2 /* Tape.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = Tape.cpp; path = Electron/Tape.cpp; sourceTree = "<group>"; };
@@ -2733,6 +2736,8 @@
 			children = (
 				4B74CF7F2312FA9C00500CE8 /* HFV.hpp */,
 				4B74CF802312FA9C00500CE8 /* HFV.cpp */,
+				4BE8EB6425C750B50040BC40 /* DAT.cpp */,
+				4BE8EB6525C750B50040BC40 /* DAT.hpp */,
 			);
 			path = Formats;
 			sourceTree = "<group>";
@@ -4770,6 +4775,7 @@
 				4B2BFDB21DAEF5FF001A68B8 /* Video.cpp in Sources */,
 				4BEDA3BF25B25563000C2DBD /* Decoder.cpp in Sources */,
 				4B4DC82B1D2C27A4003C5BF8 /* SerialBus.cpp in Sources */,
+				4BE8EB6625C750B50040BC40 /* DAT.cpp in Sources */,
 				4BBFFEE61F7B27F1005F3FEB /* TrackSerialiser.cpp in Sources */,
 				4BAE49582032881E004BE78E /* CSZX8081.mm in Sources */,
 				4B0333AF2094081A0050B93D /* AppleDSK.cpp in Sources */,
diff --git a/OSBindings/Mac/Clock Signal/Info.plist b/OSBindings/Mac/Clock Signal/Info.plist
index 7f07c53ec..83809e66f 100644
--- a/OSBindings/Mac/Clock Signal/Info.plist	
+++ b/OSBindings/Mac/Clock Signal/Info.plist	
@@ -552,6 +552,26 @@
 			<key>NSDocumentClass</key>
 			<string>$(PRODUCT_MODULE_NAME).MachineDocument</string>
 		</dict>
+		<dict>
+			<key>CFBundleTypeExtensions</key>
+			<array>
+				<string>dat</string>
+			</array>
+			<key>CFBundleTypeName</key>
+			<string>Electron/BBC Hard Disk Image</string>
+			<key>CFBundleTypeOSTypes</key>
+			<array>
+				<string>????</string>
+			</array>
+			<key>CFBundleTypeRole</key>
+			<string>Editor</string>
+			<key>LSHandlerRank</key>
+			<string>Owner</string>
+			<key>LSTypeIsPackage</key>
+			<false/>
+			<key>NSDocumentClass</key>
+			<string>$(PRODUCT_MODULE_NAME).MachineDocument</string>
+		</dict>
 	</array>
 	<key>CFBundleExecutable</key>
 	<string>$(EXECUTABLE_NAME)</string>
diff --git a/OSBindings/Mac/Clock Signal/Machine/StaticAnalyser/CSStaticAnalyser.mm b/OSBindings/Mac/Clock Signal/Machine/StaticAnalyser/CSStaticAnalyser.mm
index 71eb87247..a302b5f3c 100644
--- a/OSBindings/Mac/Clock Signal/Machine/StaticAnalyser/CSStaticAnalyser.mm	
+++ b/OSBindings/Mac/Clock Signal/Machine/StaticAnalyser/CSStaticAnalyser.mm	
@@ -99,7 +99,7 @@
 		using Target = Analyser::Static::Acorn::Target;
 		auto target = std::make_unique<Target>();
 		target->has_dfs = dfs;
-		target->has_adfs = adfs;
+		target->has_pres_adfs = adfs;
 		target->has_ap6_rom = ap6;
 		target->has_sideways_ram = sidewaysRAM;
 		_targets.push_back(std::move(target));
diff --git a/OSBindings/Qt/mainwindow.cpp b/OSBindings/Qt/mainwindow.cpp
index 8a0b781da..86afb4691 100644
--- a/OSBindings/Qt/mainwindow.cpp
+++ b/OSBindings/Qt/mainwindow.cpp
@@ -1163,7 +1163,7 @@ void MainWindow::start_electron() {
 	auto target = std::make_unique<Target>();
 
 	target->has_dfs = ui->electronDFSCheckBox->isChecked();
-	target->has_adfs = ui->electronADFSCheckBox->isChecked();
+	target->has_pres_adfs = ui->electronADFSCheckBox->isChecked();
 	target->has_ap6_rom = ui->electronAP6CheckBox->isChecked();
 	target->has_sideways_ram = ui->electronSidewaysRAMCheckBox->isChecked();
 
diff --git a/ROMImages/Electron/readme.txt b/ROMImages/Electron/readme.txt
index 995145ee9..349144e2a 100644
--- a/ROMImages/Electron/readme.txt
+++ b/ROMImages/Electron/readme.txt
@@ -8,10 +8,9 @@ DFS-1770-2.20.rom	— used only if the user opens a DFS disk image
 ADFS-E00_1.rom		— used only if the user opens an ADFS disk image
 ADFS-E00_2.rom
 AP6v133.rom			— used only if the user opens a disk image that makes use of any of the commands given below.
+adfs.rom			- used only if the user opens a hard disk image
 
 Possibly to be desired in the future:
-* adfs.rom
-* ElectronExpansionRomPresAP2-v1.23.rom
 * os300.rom
 
 Commands that trigger a request for the AP6v133 ROM:
diff --git a/Storage/MassStorage/Formats/DAT.cpp b/Storage/MassStorage/Formats/DAT.cpp
new file mode 100644
index 000000000..ceb00c7ab
--- /dev/null
+++ b/Storage/MassStorage/Formats/DAT.cpp
@@ -0,0 +1,41 @@
+//
+//  DAT.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 31/01/2021.
+//  Copyright © 2021 Thomas Harte. All rights reserved.
+//
+
+#include "DAT.hpp"
+
+using namespace Storage::MassStorage;
+
+DAT::DAT(const std::string &file_name) : file_(file_name) {
+	// Is the file a multiple of 256 bytes in size?
+	const auto file_size = file_.stats().st_size;
+	if(file_size & 255) throw std::exception();
+
+	// Does it contain the 'Hugo' signature?
+	file_.seek(0x201, SEEK_SET);
+	if(!file_.check_signature("Hugo")) {
+		throw std::exception();
+	}
+}
+
+size_t DAT::get_block_size() {
+	return 256;
+}
+
+size_t DAT::get_number_of_blocks() {
+	return size_t(file_.stats().st_size) / 256;
+}
+
+std::vector<uint8_t> DAT::get_block(size_t address) {
+	file_.seek(long(address * 256), SEEK_SET);
+	return file_.read(256);
+}
+
+void DAT::set_block(size_t address, const std::vector<uint8_t> &contents) {
+	file_.seek(long(address * 256), SEEK_SET);
+	file_.write(contents);
+}
diff --git a/Storage/MassStorage/Formats/DAT.hpp b/Storage/MassStorage/Formats/DAT.hpp
new file mode 100644
index 000000000..7ec0350e4
--- /dev/null
+++ b/Storage/MassStorage/Formats/DAT.hpp
@@ -0,0 +1,40 @@
+//
+//  DAT.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 31/01/2021.
+//  Copyright © 2021 Thomas Harte. All rights reserved.
+//
+
+#ifndef MassStorage_DAT_hpp
+#define MassStorage_DAT_hpp
+
+#include "../MassStorageDevice.hpp"
+#include "../../FileHolder.hpp"
+
+namespace Storage {
+namespace MassStorage {
+
+/*!
+	Provides a @c MassStorageDevice containing an Acorn ADFS image, which is just a
+	sector dump of an ADFS volume. It will be validated for an ADFS catalogue and communicate
+	in 256-byte blocks.
+*/
+class DAT: public MassStorageDevice {
+	public:
+		DAT(const std::string &file_name);
+
+	private:
+		FileHolder file_;
+
+		/* MassStorageDevices overrides. */
+		size_t get_block_size() final;
+		size_t get_number_of_blocks() final;
+		std::vector<uint8_t> get_block(size_t address) final;
+		void set_block(size_t address, const std::vector<uint8_t> &) final;
+};
+
+}
+}
+
+#endif /* MassStorage_DAT_hpp */
diff --git a/Storage/MassStorage/SCSI/DirectAccessDevice.cpp b/Storage/MassStorage/SCSI/DirectAccessDevice.cpp
index 2fc6039b7..f6944d2f0 100644
--- a/Storage/MassStorage/SCSI/DirectAccessDevice.cpp
+++ b/Storage/MassStorage/SCSI/DirectAccessDevice.cpp
@@ -38,6 +38,7 @@ bool DirectAccessDevice::write(const Target::CommandState &state, Target::Respon
 	if(!device_) return false;
 
 	const auto specs = state.read_write_specs();
+	LOG("Write: " << specs.number_of_blocks << " to " << specs.address);
 
 	responder.receive_data(device_->get_block_size() * specs.number_of_blocks, [this, specs] (const Target::CommandState &state, Target::Responder &responder) {
 		const auto received_data = state.received_data();
diff --git a/Storage/MassStorage/SCSI/SCSI.hpp b/Storage/MassStorage/SCSI/SCSI.hpp
index 538f1f30f..c896f7c3b 100644
--- a/Storage/MassStorage/SCSI/SCSI.hpp
+++ b/Storage/MassStorage/SCSI/SCSI.hpp
@@ -90,6 +90,13 @@ constexpr double DeskewDelay		= ns(45.0);
 /// any two devices.
 constexpr double CableSkew			= ns(10.0);
 
+/*!
+	@returns The value of the data lines per @c state.
+*/
+constexpr uint8_t data_lines(BusState state) {
+	return uint8_t(state & 0xff);
+}
+
 #undef ns
 #undef us
 
diff --git a/Storage/MassStorage/SCSI/TargetImplementation.hpp b/Storage/MassStorage/SCSI/TargetImplementation.hpp
index ff6ccb297..5a4596d1a 100644
--- a/Storage/MassStorage/SCSI/TargetImplementation.hpp
+++ b/Storage/MassStorage/SCSI/TargetImplementation.hpp
@@ -17,8 +17,8 @@ template <typename Executor> void Target<Executor>::scsi_bus_did_change(Bus *, B
 	/*
 		"The target determines that it is selected when the SEL# signal
 		and its SCSI ID bit are active and the BSY# and I#/O signals
-		are false. It then asserts the signal within a selection abort
-		time."
+		are false. It then asserts the signal within a selection
+		abort time."
 	*/
 
 	// Wait for deskew, at the very least.