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Port IO: Difference between revisions
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The x86 architecture separates the address space in two programmatically distinct groups: memory and ports. In ancient history, memory was used as the storage of data where reads and writes would not have side-effects, and ports were used to control external hardware, which needed different timings to work. Which is also why accessing ports is so much slower than accessing memory. Many other common architectures have a unified space, where devices run at the same speed as memory, or where the address space is divided into blocks with separately configurable properties.
Modern
== How to access ports ==
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== Which ports belong to this device ==
There are three groups of devices, each requiring a different approach. The first group contains all PC-AT hardware, devices like [[PIT|timers]], [[PIC|interrupt controllers]], [[
The second group is plug-and-play hardware. Most modern cards and optional features are PCI, AGP or PCI express. At boot, their requirements are checked, and the BIOS will assign port ranges to each device. Enumerating the [[PCI]] bus will list all these devices, and can also tell you what ports (and memory mapped ranges) they use.
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