>On Sun, 6 Aug 2000, Warner Losh wrote:
>>In message <[EMAIL PROTECTED]> Warner Losh writes:
>>: The reason you have a ISA to PCI bridge still is that the serial
>>: ports, parallel ports, floppy, keyboard and mouse devices still live
>>: on the ISA bus. They aren't full PCI nodes just yet in most hardware
>>: designs (I've yet to see a floppy, keyboard or mouse on the pci bus,
>>: but I'm sure people will tell me where I can find such beasts).
>>I should have also added:
>>Even though there are no ISA expansion slots on your machine, you
>>still have an ISA bus living inside (unless it is a legacy free
>>machine we keep hearing about, which I didn't think was on the
>>market). The PC-99 standard (not to be confused with the Japanese
>>PC-98 machines) states that you cannot have a ISA expansion slot, but
>>a later clarification to the standard states clearly that you can
>>still have ISA devices built into the mother board.
>>In other words, No ISA slots doesn't necessarily mean that the machine
>>doesn't have an ISA bus.
>Well, I understand that, my question is, why are true PCI devices like
>video controllers still shown as being on isa0 by the kernel? I wanted
>an explanation of that. That's what doesn't make sense to me. Perhaps
>there's a valid PC/AT hardware limitation reason for it. Otherwise it
>seems silly. =)
>Brandon D. Valentine
If you read the PCI's specification, video cards are given special
treatment due to necessary backward compatibility with ISA video
PCI video cards occupies ISA bus resources (ports and memory range)
and these are handled in a special manner which is not quite
PCI bus's way.
If a video card uses only PCI bus resources and does not occupy
any of legacy ISA bus resoruces, it is indeed silly that it is
recognized to be on the ISA bus. But, the reality is that the PCI
video card is a half-PCI and half-ISA device...
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