The magical missing 6 megabytes of mysterious RAM

Terry Lambert tlambert2 at
Wed May 7 00:10:51 PDT 2003

Laszlo Vagner wrote:
> typical BIOS chips are about 1 megabyte and there is an option in the
> bios to copy the flash bios contents into physical ram for more performance
> on some systems (some can be disabled too).
> My idea is that everything before the bios and including the kernel is
> copied to
> ram. naturally you couldnt run the kernel out of the flash memory or off
> the hard disk. Additional kernel drivers would take more ram also.

This would only make the memory reported by CMOS different from
the memory reported by the BIOS.

Since the memory reported by the CMOS is never printed for you
to see, that still leaves the kernel for the "real" vs. "avail"

BTW, if you read the code, you will see that the BIOS call used
gets memory "extents"; the holes in these extents are mapped
devices, BIOS, whatever, as reported by the BIOS.  It's accounted
in "real".

To do what you want, you would need to explicitly modify the BIOS
on your hardware to *not* count the flash as "mirrored BIOS".

Best suggestion is: treat it like a read-only disk, and boot from
it normally: let someone else (the loader) do the copy to RAM.

-- Terry

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