|I/O Mapped I/P||Memory mapped I/O|
|I/O devices are treated as I/O and memory as memory.||Both the devices i.e I/O and memory are treated as memory.|
|Device address is 8/16 bits.||Device address is 20 bits.|
|Central signals used for I/O are IOR and LOW.||Control signals used for I/O are MEMR and MEMw.|
|Larger in size due to more buses||Smaller in size|
|In this I/O address are called ports.||Normal memory address are for both.|
|Data transfer is possible between accumulator and I/O only.||Data transfer is possible between any register and I/O.|
Memory mapped IO uses one address space for memory and input and output devices. In other words, some addresses are assigned to memory while others are assigned to store the addresses of IO devices. There is one set of read and write instruction lines. The same set of instructions work for both memory and IO operations. Therefore, the instructions used to manipulate memory can be used for IO devices too. Hence, it can lessen the addressing capability of memory because some are occupied by the IO.
IO mapped IO uses two separate address spaces for memory locations and for IO devices. There are two separate control lines for both memory and IO transfer. In other words, there are different read-write instruction for both IO and memory. IO read and IO write are for IO transfer whereas memory read and memory write are for memory transfer. IO mapped IO is also called port-mapped IO or isolated IO.