Compare memory-mapped I/O with port-mapped I/O.

Memory-mapped I/O maps device registers to memory addresses - same instructions for memory and I/O, full addressing modes, but consumes address space. Port-mapped I/O uses separate address space with special instructions (IN/OUT on x86) - doesn't use memory addresses, but limited instructions. Modern systems prefer memory-mapped: easier programming, cache coherency protocols apply, works with virtual memory. x86 supports both; ARM uses memory-mapped exclusively.