I have an ASUS P2B Motherboard that has 3 dimm slots, each capable of
handling 256 MB of RM. I have each filled with 256MB RAM chips, but the
BIOS is only showing 640MB of RAM. When I do a lshw I get the following: etc.
what's going on?

Reply:
This is common on all operating systems. The amount measured is often less than
you have installed. Sometimes it is considerably less. In your case it is only
marginal. It is usually the result of memory mapping and devices that have
overlapping memory. It does not mean necessarily that you have less, just that
it is hard to get an accurate measurement due to hardware and software on your
system and the way they use memory.

For example a video card may have its own RAM, but use a small amount of the
onboard RAM, too.

What does your BIOS show? If it shows what you think then is a good thing.
Sometimes you change the BIOS so that memory is maximised and utilised as you
want. Sometimes not.

According to MS a computer with 4 GBs of RAM in Vista may show only 3 GBs of
RAM, depending on the number of devices that you have installed and your
configuration. So this is not just a Linux thing, but generic.

BTW, I have 3 GBs of RAM and it lists at 2814 MBs. I am sure that others will
find a similar thing. It is nothing to worry over. RAM is cheap now.