Witcher 3 Dev: PS4 Is A High End PC, CD Projekt Happy With New Architecture

[Pemalite]

ethomaz said:

CGI-Quality said:

This may be a bit off-topic, and a stupid question, but if you have two GPUs (SLI), each with 6GB of RAM (GDDR5 of course), are you allocated 6GB of VRAM total? I thought it did mean that, but a buddy of mine claims otherwise.

SLI uses the total RAM of the GPU that have the less RAM.

1x GPU 2GB
1x GPU 1GB

Your SLI will use only 1GB... because the used RAM on both card are mirrored.

Correct.

Simple reason for this, PCI-E and the SLI/Crossfire bridge doesn't have the bandwidth or latency required in order to share the memory contents on each card for one big fat giant memory pool.
However, if you go farther back in the cache hierachy, aka System Ram, the GPU's can all share the same memory before it gets sent off to each GPU, which is what is important for compute tasks.

However, with that said despite the memory pools having duplicated information, SLI/Crossfire still manages almost 100% scaling in dual GPU gaming scenarios, compute is a whole different ball game however.

So in the end, even though I have in total 9Gb of GDDR5 memory, only 3Gb of that is useable by games, the whole 9Gb however is available for compute. :)