System Memory per Video Memory

Hi, I have a basic question that probably has no real answer. Is there a formula or something that will tell me how much system memory is reserved per video card memory, pci-e of course. I know how memory mapping works in general, I just don't know this!

I ask because I have a 128MB video card on a 4GB system, and my system memory is down to 3.5GB. That's 1:4! (Of course there's other things that reserve memory too). But of course, assuming linearity then a 512MB video card would map 2GB of system memory, which I know is wrong.

?

Actually, you may be missing a fundamental part of the equation. 32-bit Operating systems cannot use the full 4 gigs, so you're already handicapped to begin with. Subtract the 128MB of VRAM and without doing precise calcs, off the top of my head I'd say you're right about what you quoted.

So the answer: it's certainly not 4:1. I'm pretty sure it's 1:1, but you don't have full 4 gigs to start with ;)

If you upgrade to a 64-bit OS, you'll be able to use the full 4GB of RAM.

Actually, a 32 bit operating system CAN access the full 4GB of ram. However the computer allocates some of the upper high end for memory mapped devices. If you didn't have any memory mapped, an OS could get the full 4GB. But in the end, Windows XP sets a soft limit for driver compatibility.

But that wasn't the question I asked. So 1:1 it is. Thank you.