diff --git a/Machines/Acorn/Archimedes/InputOutputController.hpp b/Machines/Acorn/Archimedes/InputOutputController.hpp
index 3ebbc33f3..ac7e6e18c 100644
--- a/Machines/Acorn/Archimedes/InputOutputController.hpp
+++ b/Machines/Acorn/Archimedes/InputOutputController.hpp
@@ -113,87 +113,110 @@ struct InputOutputController {
 		}
 	}
 
-	static constexpr uint32_t AddressMask = 0x1f'ffff;
+	/// Decomposes an Archimedes bus address into bank, offset and type.
+	struct Address {
+		constexpr Address(uint32_t bus_address) noexcept {
+			bank = (bus_address >> 16) & 0b111;
+			type = Type((bus_address >> 19) & 0b11);
+			offset = bus_address & 0b1111100;
+		}
+
+		/// A value from 0 to 7 indicating the device being addressed.
+		uint32_t bank;
+		/// A seven-bit value which is a multiple of 4, indicating the address within the bank.
+		uint32_t offset;
+		/// Access type.
+		enum class Type {
+			Sync = 0b00,
+			Fast = 0b01,
+			Medium = 0b10,
+			Slow = 0b11
+		} type;
+	};
 
 	bool read(uint32_t address, uint8_t &value) {
-		const auto target = address & AddressMask;
+		const Address target(address);
 		value = 0xff;
-		switch(target) {
+
+		switch(target.bank) {
 			default:
-				logger.error().append("Unrecognised IOC read from %08x", address);
+				logger.error().append("Unrecognised IOC read from %08x i.e. bank %d / type %d", address, target.bank, target.type);
 			break;
 
-			case 0x3200000 & AddressMask:
-				value = control_ | 0xc0;
-				value &= ~(i2c_.clock() ? 2 : 0);
-				value &= ~(i2c_.data() ? 1 : 0);
-//				logger.error().append("IOC control read: C:%d D:%d", !(value & 2), !(value & 1));
-			return true;
+			// Bank 0: internal registers.
+			case 0:
+				switch(target.offset) {
+					default:
+						logger.error().append("Unrecognised IOC bank 0 read; offset %02x", target.offset);
+					break;
 
-			case 0x3200004 & AddressMask:
-				value = serial_.input(IOCParty);
-				irq_b_.clear(IRQB::KeyboardReceiveFull);
-				observer_.update_interrupts();
-//				logger.error().append("IOC keyboard receive: %02x", value);
-			return true;
+					case 0x00:
+						value = control_ | 0xc0;
+						value &= ~(i2c_.clock() ? 2 : 0);
+						value &= ~(i2c_.data() ? 1 : 0);
+//						logger.error().append("IOC control read: C:%d D:%d", !(value & 2), !(value & 1));
+					break;
 
-			// IRQ A.
-			case 0x3200010 & AddressMask:
-				value = irq_a_.status;
-//				logger.error().append("IRQ A status is %02x", value);
-			return true;
-			case 0x3200014 & AddressMask:
-				value = irq_a_.request();
-//				logger.error().append("IRQ A request is %02x", value);
-			return true;
-			case 0x3200018 & AddressMask:
-				value = irq_a_.mask;
-//				logger.error().append("IRQ A mask is %02x", value);
-			return true;
+					case 0x04:
+						value = serial_.input(IOCParty);
+						irq_b_.clear(IRQB::KeyboardReceiveFull);
+						observer_.update_interrupts();
+//						logger.error().append("IOC keyboard receive: %02x", value);
+					break;
 
-			// IRQ B.
-			case 0x3200020 & AddressMask:
-				value = irq_b_.status;
-//				logger.error().append("IRQ B status is %02x", value);
-			return true;
-			case 0x3200024 & AddressMask:
-				value = irq_b_.request();
-//				logger.error().append("IRQ B request is %02x", value);
-			return true;
-			case 0x3200028 & AddressMask:
-				value = irq_b_.mask;
-//				logger.error().append("IRQ B mask is %02x", value);
-			return true;
+					// IRQ A.
+					case 0x10:
+						value = irq_a_.status;
+//						logger.error().append("IRQ A status is %02x", value);
+					break;
+					case 0x14:
+						value = irq_a_.request();
+//						logger.error().append("IRQ A request is %02x", value);
+					break;
+					case 0x18:
+						value = irq_a_.mask;
+//						logger.error().append("IRQ A mask is %02x", value);
+					break;
 
-			// FIQ.
-			case 0x3200030 & AddressMask:
-				value = fiq_.status;
-				logger.error().append("FIQ status is %02x", value);
-			return true;
-			case 0x3200034 & AddressMask:
-				value = fiq_.request();
-				logger.error().append("FIQ request is %02x", value);
-			return true;
-			case 0x3200038 & AddressMask:
-				value = fiq_.mask;
-				logger.error().append("FIQ mask is %02x", value);
-			return true;
+					// IRQ B.
+					case 0x20:
+						value = irq_b_.status;
+//						logger.error().append("IRQ B status is %02x", value);
+					break;
+					case 0x24:
+						value = irq_b_.request();
+//						logger.error().append("IRQ B request is %02x", value);
+					break;
+					case 0x28:
+						value = irq_b_.mask;
+//						logger.error().append("IRQ B mask is %02x", value);
+					break;
 
-			// Counters.
-			case 0x3200040 & AddressMask:
-			case 0x3200050 & AddressMask:
-			case 0x3200060 & AddressMask:
-			case 0x3200070 & AddressMask:
-				value = counters_[(target >> 4) - 0x4].output & 0xff;
-//				logger.error().append("%02x: Counter %d low is %02x", target, (target >> 4) - 0x4, value);
-			return true;
+					// FIQ.
+					case 0x30:
+						value = fiq_.status;
+						logger.error().append("FIQ status is %02x", value);
+					break;
+					case 0x34:
+						value = fiq_.request();
+						logger.error().append("FIQ request is %02x", value);
+					break;
+					case 0x38:
+						value = fiq_.mask;
+						logger.error().append("FIQ mask is %02x", value);
+					break;
 
-			case 0x3200044 & AddressMask:
-			case 0x3200054 & AddressMask:
-			case 0x3200064 & AddressMask:
-			case 0x3200074 & AddressMask:
-				value = counters_[(target >> 4) - 0x4].output >> 8;
-//				logger.error().append("%02x: Counter %d high is %02x", target, (target >> 4) - 0x4, value);
+					// Counters.
+					case 0x40:	case 0x50:	case 0x60:	case 0x70:
+						value = counters_[(target.offset >> 4) - 0x4].output & 0xff;
+//						logger.error().append("%02x: Counter %d low is %02x", target, (target >> 4) - 0x4, value);
+					break;
+
+					case 0x44:	case 0x54:	case 0x64:	case 0x74:
+						value = counters_[(target.offset >> 4) - 0x4].output >> 8;
+//						logger.error().append("%02x: Counter %d high is %02x", target, (target >> 4) - 0x4, value);
+					break;
+				}
 			return true;
 		}
 
@@ -201,113 +224,109 @@ struct InputOutputController {
 	}
 
 	bool write(uint32_t address, uint8_t value) {
-		const auto target = address & AddressMask;
-		switch(target) {
+		const Address target(address);
+		switch(target.bank) {
 			default:
-				logger.error().append("Unrecognised IOC write of %02x at %08x", value, address);
+				logger.error().append("Unrecognised IOC write of %02x to %08x i.e. bank %d / type %d", value, address, target.bank, target.type);
 			break;
 
-			case 0x320'0000 & AddressMask:
-				// TODO: does the rest of the control register relate to anything?
-				control_ = value;
-				i2c_.set_clock_data(!(value & 2), !(value & 1));
-			return true;
+			// Bank 0: internal registers.
+			case 0:
+				switch(target.offset) {
+					default:
+						logger.error().append("Unrecognised IOC bank 0 write; %02x to offset %02x", value, target.offset);
+					break;
 
-			case 0x320'0004 & AddressMask:
-				serial_.output(IOCParty, value);
-				irq_b_.clear(IRQB::KeyboardTransmitEmpty);
-				observer_.update_interrupts();
-			return true;
+					case 0x00:
+						// TODO: does the rest of the control register relate to anything?
+						control_ = value;
+						i2c_.set_clock_data(!(value & 2), !(value & 1));
+					break;
 
-			case 0x320'0014 & AddressMask:
-				// b2: clear IF.
-				// b3: clear IR.
-				// b4: clear POR.
-				// b5: clear TM[0].
-				// b6: clear TM[1].
-				irq_a_.clear(value & 0x7c);
-				observer_.update_interrupts();
-			return true;
+					case 0x04:
+						serial_.output(IOCParty, value);
+						irq_b_.clear(IRQB::KeyboardTransmitEmpty);
+						observer_.update_interrupts();
+					break;
 
-			// Interrupts.
-			case 0x320'0018 & AddressMask:	irq_a_.mask = value;	return true;
-			case 0x320'0028 & AddressMask:	irq_b_.mask = value;	return true;
-			case 0x320'0038 & AddressMask:	fiq_.mask = value;		return true;
+					case 0x14:
+						// b2: clear IF.
+						// b3: clear IR.
+						// b4: clear POR.
+						// b5: clear TM[0].
+						// b6: clear TM[1].
+						irq_a_.clear(value & 0x7c);
+						observer_.update_interrupts();
+					break;
 
-			// Counters.
-			case 0x320'0040 & AddressMask:
-			case 0x320'0050 & AddressMask:
-			case 0x320'0060 & AddressMask:
-			case 0x320'0070 & AddressMask:
-				counters_[(target >> 4) - 0x4].reload = uint16_t(
-					(counters_[(target >> 4) - 0x4].reload & 0xff00) | value
-				);
-			return true;
+					// Interrupts.
+					case 0x18:	irq_a_.mask = value;	break;
+					case 0x28:	irq_b_.mask = value;	break;
+					case 0x38:	fiq_.mask = value;		break;
 
-			case 0x320'0044 & AddressMask:
-			case 0x320'0054 & AddressMask:
-			case 0x320'0064 & AddressMask:
-			case 0x320'0074 & AddressMask:
-				counters_[(target >> 4) - 0x4].reload = uint16_t(
-					(counters_[(target >> 4) - 0x4].reload & 0x00ff) | (value << 8)
-				);
-			return true;
+					// Counters.
+					case 0x40:	case 0x50:	case 0x60:	case 0x70:
+						counters_[(target.offset >> 4) - 0x4].reload = uint16_t(
+							(counters_[(target.offset >> 4) - 0x4].reload & 0xff00) | value
+						);
+					break;
 
-			case 0x320'0048 & AddressMask:
-			case 0x320'0058 & AddressMask:
-			case 0x320'0068 & AddressMask:
-			case 0x320'0078 & AddressMask:
-				counters_[(target >> 4) - 0x4].value = counters_[(target >> 4) - 0x4].reload;
-			return true;
+					case 0x44:	case 0x54:	case 0x64:	case 0x74:
+						counters_[(target.offset >> 4) - 0x4].reload = uint16_t(
+							(counters_[(target.offset >> 4) - 0x4].reload & 0x00ff) | (value << 8)
+						);
+					break;
 
-			case 0x320'004c & AddressMask:
-			case 0x320'005c & AddressMask:
-			case 0x320'006c & AddressMask:
-			case 0x320'007c & AddressMask:
-				counters_[(target >> 4) - 0x4].output = counters_[(target >> 4) - 0x4].value;
-			return true;
+					case 0x48:	case 0x58:	case 0x68:	case 0x78:
+						counters_[(target.offset >> 4) - 0x4].value = counters_[(target.offset >> 4) - 0x4].reload;
+					break;
 
-			case 0x327'0000 & AddressMask:
-				logger.error().append("TODO: exteded external podule space");
-			return true;
-
-			case 0x331'0000 & AddressMask:
-				logger.error().append("TODO: 1772 / disk write");
-			return true;
-
-			case 0x335'0000 & AddressMask:
-				logger.error().append("TODO: LS374 / printer data write");
-			return true;
-
-			case 0x335'0018 & AddressMask:
-				logger.error().append("TODO: latch B write: %02x", value);
-			return true;
-
-			case 0x335'0040 & AddressMask:
-				logger.error().append("TODO: latch A write: %02x", value);
-			return true;
-
-			case 0x335'0048 & AddressMask:
-				logger.error().append("TODO: latch C write: %02x", value);
-			return true;
-
-			case 0x336'0000 & AddressMask:
-				logger.error().append("TODO: podule interrupt request");
-			return true;
-
-			case 0x336'0004 & AddressMask:
-				logger.error().append("TODO: podule interrupt mask");
-			return true;
-
-			case 0x33a'0000 & AddressMask:
-				logger.error().append("TODO: 6854 / econet write");
-			return true;
-
-			case 0x33b'0000 & AddressMask:
-				logger.error().append("TODO: 6551 / serial line write");
-			return true;
+					case 0x4c:	case 0x5c:	case 0x6c:	case 0x7c:
+						counters_[(target.offset >> 4) - 0x4].output = counters_[(target.offset >> 4) - 0x4].value;
+					break;
+				}
+				return true;
 		}
 
+//			case 0x327'0000 & AddressMask:	// Bank 7
+//				logger.error().append("TODO: exteded external podule space");
+//			return true;
+//
+//			case 0x331'0000 & AddressMask:
+//				logger.error().append("TODO: 1772 / disk write");
+//			return true;
+//
+//			case 0x335'0000 & AddressMask:
+//				logger.error().append("TODO: LS374 / printer data write");
+//			return true;
+//
+//			case 0x335'0018 & AddressMask:
+//				logger.error().append("TODO: latch B write: %02x", value);
+//			return true;
+//
+//			case 0x335'0040 & AddressMask:
+//				logger.error().append("TODO: latch A write: %02x", value);
+//			return true;
+//
+//			case 0x335'0048 & AddressMask:
+//				logger.error().append("TODO: latch C write: %02x", value);
+//			return true;
+//
+//			case 0x336'0000 & AddressMask:
+//				logger.error().append("TODO: podule interrupt request");
+//			return true;
+//
+//			case 0x336'0004 & AddressMask:
+//				logger.error().append("TODO: podule interrupt mask");
+//			return true;
+//
+//			case 0x33a'0000 & AddressMask:
+//				logger.error().append("TODO: 6854 / econet write");
+//			return true;
+//
+//			case 0x33b'0000 & AddressMask:
+//				logger.error().append("TODO: 6551 / serial line write");
+//			return true;
 		return true;
 	}