Random idea about video memory

monktus

monktus

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I had a random (probably unfeasable) idea about video memory.

Now you'll all know that some PCs use shared video memory (borrowed from the system RAM), I'm curious as to whether this is controlled in hardware or by the OS. The reason why is that I was wondering if it would be possible (on a Mac, in theory at least) to write a bit of software to 'borrow' RAM from the system and add it to the VRAM (a bit like virtual memory but using proper RAM). I assume that all the memory management on a video card is done on board but I thought that it would be interesting if there was a way of changing this with drivers or other software.

A bit random I know but it would be nice if I could get my 32mb Radeon to borrow some of my 768mb of system RAM :)
 
Most modern operating systems do this already. What you see on the PC as "share video memory" usually is because the graphics chip is integrated on the mother board, they don't have room to solder VRAM modules so they just borrow system RAM. This is possible without a performance hit because of the AGP bus. AGP allows graphics chips to access system RAM faster than the PCI bus can because it bypasses the need to go through the north bridge, and the path between AGP and sys RAM is 66 MHz rather than 33 MHz of PCI.

So any platform/OS that supports AGP is already doing the shared video memory function. Even you Mac is doing it right now ;) No extra software needed.
 
Ah interesting. But it would still be benficial to add another 32mb or whatever of dedicated memory to compliment the VRAM on the card, I was just wondering how feasible it would be to do this with software.
 
With MacOSX using Quartz Extreme, it's VERY beneficial because QE uses up a lot of video memory for drawing (texture memory to be exact).

But the problem lies in driver support for the video cards. You'd have to convince Apple to invest development time into it, this is not something Joe Programmer can do at home in his free time. Apple has the license from ATI and Nvidia, we don't. Apple engineers have a better understanding and better docs on said video cards, we don't. You see the trend?
 
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