WinXP RAM Available with 3 Different Video Cards in 4GB Environment.

I'm optimizing my recording computer/Digital Audio Workstation (DAW) for Windows XP SP3. I can not move to Win 7 due to flaky drivers for my two Delta 1010LT audio input cards. Each card has 8 audio inputs and all 16 are cabled into my home recording studio.

My DAW is an MSI P43 Neo3 (MS-7514) motherboard with 4 GB RAM. CPU is an Intel Core2 Quad Q9650 @ 3GHz. I'm running dual 1920 x 1200 monitors.

With a 512mb PCI Express 16 video card available RAM drops to 2.75 GB

I then tried a 256MB PCI Express 16 video card available RAM increases to 3.0 GB.

Next up was an ATI Radeon X600 video card with 128mb. Available RAM jumps to 3.5 GB.

(I ordered a 64mb video card that is clearly marked 64mb but really has 256mb (verified by the Windows driver and CPU-Z) so I don't know how much RAM will be available with a 64MB video card).

With a 512mb card WinXP loses 1.25GB of RAM.
With a 256mm card WinXP loses 1.0 GB of RAM.
With a 128mb card WinXP loses 512MB of RAM.

I understand that the video RAM has to mapped in the 4 GB 32bit memory space but why does XP lose at lease double the amount of RAM on the video card? I would expect XP to lose the amount of RAM on the video card and maybe a bit more but double the amount? And with a 128mb card it loses 4 times the video RAM.

With 2 GB of RAM installed on the motherboard XP loses ZERO ram with the 512MB card installed. So all the video card has is 512MB that is on the card and nothing else. Yet with 4 GB installed the video card causes a 1.25 GB drop in RAM.

Does anyone know why the memory penalty is so great in a 4GB environment?

The good news is that I have yet to max out the CPU or RAM demands when recording and Sonar X1 is very happy with 2.75 GB of RAM. I'm using the 128MB video card and it has no problems with the two 1920 x 1200 monitors.

My WinXP SP3 DAW computer is far more secure than my Win 7 system. It's not connected to the internet !