Compare memory mapped I/O with I/O mapped I/O.
Memory Mapped I/O Scheme: In this scheme there is only one address space. Address space is stated as all possible addresses that microprocessor can generate. Some addresses are allocated to memories and some addresses to I/O devices. An I/O device is also treated just like a memory location and one address is assigned to it. In this scheme all the data transfer instructions of microprocessor can be used for both memory and I/O device. This scheme is suitable for a small system.
In I/O mapped I/O scheme addresses assigned to memory locations can also be assigned to I/O devices. As the same address may be assigned to a memory location or an I/O device, microprocessor should issue a signal to distinguish whether the address on address bus is for a memory location or an I/O device.