Ram Not Showing

[Hal Vaughan <hal@thresholddigital.com>]

I had 1.5 GB  (333 Mhz) in a system running Sarge with a 2.6 kernel and all of 
it was used.  I've just replaced the .5 GB stick with a 1 GB stick, giving me 
2 GB of RAM.  When I boot, the motherboard reports 2 GB, but when I check:

[root@threshnet:root]$ cat /proc/meminfo
MemTotal:       906736 kB
MemFree:        685608 kB
Buffers:          5288 kB
Cached:          36948 kB
SwapCached:          0 kB
Active:         177848 kB
Inactive:        20896 kB
HighTotal:           0 kB
HighFree:            0 kB
LowTotal:       906736 kB
LowFree:        685608 kB
SwapTotal:      120476 kB
SwapFree:       120476 kB
Dirty:            1564 kB
Writeback:           0 kB
Mapped:         166400 kB
Slab:            12468 kB
Committed_AS:   289708 kB
PageTables:        760 kB
VmallocTotal:   122800 kB
VmallocUsed:      3012 kB
VmallocChunk:   119324 kB

The motherboard uses onboard RAM for the onboard video, but that still doesn't 
explain why the motherboard reports 2GB and Linux seems to be using less than 
1 GB of RAM.  I'm actually better off with the .5GB stick in place of the 1GB 
stick.  What can I do to get Linux to use all the RAM?

Thanks!

Hal