Clever Geek Handbook

PCI address spaces

I have a question about PCI. PCI has three address spaces; PCI I / O, PCI Memory and PCI Configuration. Where are they physically located? In a PCI controller? Or in devices? Are any of them part of the system RAM?

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For physical pluggable PCI cards, it is always on the device. The device must declare that it is (config space) and keep this local state independent of the host (I / O and memory space)

PCI is often overused as a configuration mechanism, and there are many devices that don't actually talk to the PCI interface, but only fake it - PCI Express cards always show up as a PCI device, but the magical 33MHz bus that would be in between would magically disappeared.



Almost everything integrated into a chipset these days, most PCI devices are such fakes. However, they still support whatever PCI dictates. For example, the integrated graphics on your northbridge will use system memory, but for all the bats that the graphics device uses, the computer will tell the operating system that the same RAM does not exist.

As far as the OS is concerned, the device will always have its own memory.

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