Port-mapped IO
lastmod 2026-11-10created 2025-11-123 edits
Port-mapped I/O is a method in which the CPU exchanges data with peripheral devices through an I/O port address space set up separately from the memory address space. On x86, ports are accessed by specifying a port number with dedicated instructions such as in and out; it does not consume memory addresses, but in exchange it requires dedicated instructions and bus signals. It contrasts with memory-mapped I/O, which reads and writes device registers like ordinary memory; most modern systems use the latter, and port I/O remains in legacy devices.