Port Input and Output Compared With Memory Mapping
Some processors, x86 especially, have a second, older way to reach devices: a separate address space reached only by special instructions rather than by ordinary loads and stores. That is port input and output, and modern devices mostly do not use it. You need to recognise it because old documentation and old drivers are full of it, and because the two kinds of address look alike in a datasheet but must be accessed with different calls.
Questions this Concept answers
- Why must a driver know which kind of region a device advertises before it touches that region?
Memory Mapped IO versus IO Mapped IO in Computer Architecture
Memory-mapped I/O and I/O-mapped I/O are two competing schemes for how a processor addresses peripheral devices: memory-mapped I/O assigns peripherals addresses within the same unified address space …