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    SubjectRe: how to tell linux (on x86) to ignore 1M or memory
    On 06/22/2007 03:46 AM, H. Peter Anvin wrote:

    > Rene Herman wrote:
    >> On 04/19/2007 04:18 PM, Bart Trojanowski wrote:
    >>> I need to preserve some state from the bios before entering protected
    >>> mode. For now I want to copy it into some ram accessible by
    >>> real-mode, say the last megabyte visible in real-mode.
    >>> What's the easiest way to have linux ignore the megabyte starting at 15M?
    >> Note that real-mode can only access the first megabyte (*) and not the
    >> first 16. 16MB is the 16-bit protected mode (286) limit.
    > No, 16-bit protected mode (on 386+) is not limited to 16 MB.

    That all depends on one's definition of 16-bit protected mode. The "(286)"
    after mine meant I was talking about the definition in which descriptors
    have a 24-bit base (and 16-bit limit) field -- ie, real 286 and arguably,
    "real 16-bit protected mode".

    Yes, I guess another valid definition is "code with a 16-bit address and
    operand size default" on a 386+ and sure, that's just flipping a bit away.
    In the context of Linux I agree it's also a sensible definition, so, well,
    whatever. The point was that real mode could only access the first 1M, not
    the first 16... :-)


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      Last update: 2007-06-22 15:23    [W:0.022 / U:1.940 seconds]
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