Memory-mapped IO
lastmod 2025-11-12created 2017-02-214 edits
Memory-mapped I/O (MMIO) is a method in which, when a microprocessor (CPU) accesses I/O devices, the I/O and memory address spaces are not separated but are treated and laid out as a single memory space. In other words, the memory or registers of I/O devices are treated as memory and allocated to a specific region of the overall memory address space as part of the whole memory. Because the memory addresses of I/O devices are not separate, they share the same address space as memory, so they are accessed with the same machine code instructions. Whereas I/O-mapped I/O has a separate address space, memory-mapped I/O is just one part of memory.