Editing Intel 8080 (section)

====Input output port space====
The 8080 supports 256 [[input/output]] (I/O) ports,<ref>Note: Some Intel datasheets from the 1970s advertise 512 I/O ports, because they count input and output ports separately.</ref> accessed via dedicated I/O instructions taking port addresses as operands.<ref>{{cite book |title=Computer Architecture and Organization |last1=HAYES
  |first1=JOHN P. |isbn=0-07-027363-4 |year=1978 |publisher= McGraw-Hill|pages=420–423 }}</ref> This I/O mapping scheme is regarded as an advantage, as it frees up the processor's limited address space. Many CPU architectures instead use so-called [[memory-mapped I/O]] (MMIO), in which a common address space is used for both RAM and peripheral chips. This removes the need for dedicated I/O instructions, although a drawback in such designs may be that special hardware must be used to insert wait states, as peripherals are often slower than memory. However, in some simple 8080 computers, I/O is indeed addressed as if they were memory cells, "memory-mapped", leaving the I/O commands unused. I/O addressing can also sometimes employ the fact that the processor outputs the same 8-bit port address to both the lower and the higher address byte (i.e., {{code|IN 05h}} would put the address 0505h on the 16-bit address bus). Similar I/O-port schemes are used in the backward-compatible Zilog Z80 and Intel 8085, and the closely related x86 microprocessor families.