Compare memory mapped I/O with I/O mapped I/O.
Memory Mapped I/O Scheme: In this type of scheme there is merely one address space. These address space is explained as all possible addresses which microprocessor can create. Several addresses are allocated to memories and several addresses to I/O devices. That I/O device is also functions as a memory location and one address is assigned to that. In such scheme all the data transfer instructions of the microprocessor can be utilized for both I/O device and memory also. This scheme is suitable for a small system.
Within I/O mapped I/O scheme the addresses assigned to memory locations can also be assigned to I/O devices. Because the same address may be assigned to a memory location or an I/O device, microprocessor should issue a signal to distinguish when the address on the address bus is for a certain memory location or an I/O device.