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    SubjectRe: PCI mapping on large memory 32-bit machines
    On Mon, 19 May 2003, Timothy Miller wrote:

    > On x86 with PAE and 4 gigs of RAM or more, where do memory-mapped I/O
    > devices get mapped (in the physical address space)? Most PCI devices
    > can't handle 64-bit addresses. Can PC chipsets physically remap some of
    > the RAM to above 4 gig? Or do you just lose that much RAM? If both RAM
    > and some I/O device are mapped to the same location, isn't there a conflict?

    The answer to PC/PCI is that the I/O space set (usually by the BIOS)
    into the BARs removes any RAM visibility in that area. But.... this
    is BAD bacause the BIOS may still claim that there is 4 gig of RAM.
    The OS may then try to use it. To "solve" this problem, Win/tell started
    the "high-RAM" specification where RAM higher than XXX Megs gets
    mapped with page-registers. The problem is that "XXX" is board-specific!

    So, to answer your entire question... don't do it! Only use 3 gigs max
    and you will not be confused by confused hardware!

    Dick Johnson
    Penguin : Linux version 2.4.20 on an i686 machine (797.90 BogoMips).
    Why is the government concerned about the lunatic fringe? Think about it.

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