Boris Vorontsov from ENBseries has a theory on GTX 970 VRAM

Original post from link: https://www.reddit.com/r/pcgaming/comments/2uco43/boris_vorontsov_from_enbseries_has_a_theory_on/

Boris Vorontsov from ENBseries claims that the GTX 970 actually only has 3.5GB of usable VRAM at any given moment and that system RAM is used in place of the last 0.5GB of VRAM. He also claims that this can be easily proven by allocating blocks into VRAM and then dumping system RAM. By searching the dump, you can find the codes of those last 0.5GB blocks of 'VRAM'. Here's a screenshot of his comment from the PCPER's article from Januray 28, 2015 which talks about 970's memory performance:

    http://i.imgur.com/Lrzlnpj.jpg

Here are two screenshots from his Facebook page 'ENBSeries':

    http://i.imgur.com/UBEVQqw.jpg

    http://i.imgur.com/7vsjK7p.jpg

This, in my opinion, is an interesting theory on the 970's VRAM controversy and apparently it can be easily proven, as well.

Also, many people on Nvidia's forums are claiming sudden high system RAM and pagefile usage when using MSI Kombustor to test VRAM, particularly when testing the last 1gb of the 970's VRAM. Apparently, once the benchmark reaches 3gb of VRAM, system RAM and pagefile suddenly shoot up to 6-9GB (depending on how much RAM you have installed). One user posted: "Do the 1 GB test, then the 2 GB test, the program should use under 1000 MB of system memory. Watch your System RAM and page file shoot up ridiculously with the 3 GB test. It's like the whole framebuffer is being off-loaded to system memory."

I might try doing both the memory dump test and the MSI Kombustor test later tomorrow and come back with the results. If anyone else with a GTX 970 is willing to do these tests, that would be great.

edit: I tried using Nai's benchmark to test the 970's memory performance on 800MHz RAM and stock GTX970, 800MHz RAM and @7800MHz GTX970 (+800MHz from stock), 1600MHz RAM and stock GTX970, 1600MHz RAM @7800MHz GTX970.

I ran the test 2+ times (on some I ran it 5+ times but the results were the same) for each RAM and VRAM setting.

The results are as follows:

RAM at 800MHz, stock 970 (drops to 12-16gb/s, on a 5th or 6th run went up to 18gb/s and then went down to 12-16gb/s again, everything else seems to be the same):

    http://i.imgur.com/iGDLRfF.jpg

    http://i.imgur.com/6quiZUy.jpg

RAM at 800MHz, 7800MHz 970: (almost identical to the stock 970 runs)

    http://i.imgur.com/YZEQPwS.jpg

    http://i.imgur.com/tqkTSq4.jpg

    (after a 5th or so run, it got to 18gb/s, on a sixth went down to 13-16gb/s) http://i.imgur.com/udN9WXU.jpg

RAM at 1600MHz, stock 970 (consistently only drops to 20.15GB/s and no lower, everything else seems to be the same):

    http://i.imgur.com/XQ0lg5C.jpg

    http://i.imgur.com/m4nSWWZ.jpg

    http://i.imgur.com/eGZs7Uq.jpg

RAM at 1600MHz, 7800MHz 970 (again, only drops to around 20.15gb/s and no lower and no higher, everything else seems to be the same)

    http://i.imgur.com/h1qYMjF.jpg

    http://i.imgur.com/wpjkTSl.jpg

Conclusion: The only difference between all of these runs at different RAM and GPU memory speeds is the last number in the DDR test which when at a RAM clock of 800Mhz is lower than at 1600MHz, all the other numbers are almost the same. Surprisingly, overclocking the 970 made absolutely no change to any of the numbers which is very strange to say the least. I'd expected to reach more than ~155GB/s at an overclock of 800MHz to the GPU memory (7000Mhz to 7800MHz), but apparently it changed nothing. Maybe it's an issue with the benchmark or maybe it's the card, who knows.

Tomorrow, I Might try the memory dump test, MSI Kombustor benchmark and filling RAM up to 8gb and running a benchmark on the 970. It's 6:30am here where I live, so I'll be going to sleep now.

I urge everyone with a 970 to do these tests and post back the results. We need more than just 1 person doing these benchmarks.

edit #2: I just tried the AIDA64 RAM stress test which filled up the RAM to almost full 8gb. I tried running Nai's benchmark while the RAM was almost full, but my screen went black halfway through and Nvidia's driver crashed. So, there's that... If anyone knows any other programs that fill up the RAM, let me know.

edit #3: I just tried disabling pagefile and games constantly crashed or absolutely never reached over 3.3-3.5GB of VRAM (SoM, Far Cry 4). Try it yourself.