wtf_man wrote on Mar 12, 2014, 15:48:
Creston wrote on Mar 12, 2014, 15:06:
It just has to do with how much memory you have on your GPU. You can even easily test it. Just swap out the 512MB card with a 2GB one, and watch how your available system memory plummets.
I'll have to check that out! I always thought is was system drivers and RAM reserved for onboard graphics... not a discrete card.
Even an old dog learns new tricks from time to time.
Generally the OS reserves the top 512MB for memory mappings (whether you really have memory or not). So even if you have 4GB, you only have at most 3.5GB available.
Note that the discrete GPUs do NOT map their whole RAM to the system RAM, it would make no sense. Only frame buffers are mapped, and that's a tiny amount.
If the OS needs more for hardware mapping than the top 512MB, it will add a chunk of 256MB I think, and keep going. If you find that your OS can't use nowhere near the amount of RAM that you're supposed to be able to use, chances are that some of the RAM is deficient.