Suspicious physical memory map from BIOS

[questions]

Hi,

I have some problem with physical memory being getting reported incorrectly
on Freebsd 6.3. I have 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