My new machine has 4GB RAM, the BIOS sees it just fine, but Windows XP Pro only sees a little over 3GB. Googling this phenomenon turns up nuggets of info that explain PCI devices take up much of this space.

I verified this by taking out my second video card, and the Windows memory jumped to roughly 3.5GB. Conversely, when I take 1GB out, and go down to 3, I still see all 3.

Can anyone explain why PCI devices steal system RAM, but only when there is 4GB installed in the machine? Also, why wouldn't that memory appear to Windows at all? I would expect the device resources to be listed somewhere.