> What exactly is the significance of the amount of on-board RAM? I
> realise it's used for holding texture data, but what happens if the data
> doesn't all fit? Does the program just point-blank refuse to work, or
> does it merely cause a reduction in performance?

If the data doesn't all fit, the GPU will simply overwrite the RAM that 
hasn't been used for the longest and carry on (a bit like a circular 
buffer). This is not an ideal situation if you are trying to use 600MB 
of textures per frame on a card with 512MB RAM, because obviously every 
single frame you'll be transferring texture data between system RAM and 
video RAM (which is relatively slow).

Needless to say games are written to avoid this situation, they will 
select which size textures or compression to use based on the amount of 
video RAM you have. There is probably a minimum amount that below which 
the game will refuse to run, but the GPU won't actually error out if you 
try and load too many textures.

Or there are more complex algorithms, like keeping some "core" low res 
textures for everything in VRAM all the time, then only swapping in the 
high res versions for things near you in the world. If you can only move 
around the world at a certain speed then you can plan to pre-load the 
high res textures seamlessly.

Post a reply to this message