x86_64 - 4 Gig DRAM 500Meg missing

[Wolfgang S. Rupprecht]

I'm trying to understand what I need to do to make the last 500Meg of
my 4GB memory visible on a FC4 x86_64.  I assume that the 3.5GB - 4GB
area is being used for hardware and I need to arrange for the memory
to be mapped elsewhere.

My motherboard, a tyan k8e (s2865) has entries in the bios for
something called:

          S/W memory hole Remapping     disable / enable
          H/W memory hole Remapping     disable / enable
          MTRR mapping mode             continuous / discrete
 
It looked like one or both of the first two entries would do the
trick, but when I enabled them all that happened was my add-in network
card stopped working.  At boot dhcp was unable to get an address and
booting hung at that point.  This happened s/w or h/w remapping was
active (either singly or together.  I have no idea what the third item
is used for, the motherboard "manual" is a joke with it simply
repeating the same meaningless phrase with no explanation.

Hints?  I'd really like to use all 4 Gigs.

-wolfgang
-- 
Wolfgang S. Rupprecht                http://www.wsrcc.com/wolfgang/