Suspicious physical memory map from BIOS

[questions]

Hi,

I am sorry if this isn't the correct mailing list to ask my question.
Actually, I posted this on freebsd-questions list but didn't get any reply.
I couldn't find any better mailing list to post this question on.

I have some problem with physical memory being getting reported incorrectly
on Freebsd 6.3. I have a Xeon series 5300 CPU with 4GB of RAM installed but
BIOS call actually returns following usable physical memory map -

base address = 0, length = 640K
base address = 1M, length = 2.5G
base address = 4G, length = 5.5G

How am I getting this third segment?
Also, in function getmemsize() in machdep.c, why the variable 'Maxmem' is
set to 'Maxmem*4' when hw.physmem and the
highest page number obtained from physical memory map don't match?

Any help with this would be wonderful.

Thanks,
Fahad