Nvidia’s second top tier graphics card the “GTX 970” at first glance would be the GPU of choice for all gamers “hardcore or casual” but unfortunately has a weird secret that Nvidia didn’t reveal until now..
However to further understand what the issue is I need to explain a little bit about the GPU itself. Both the GTX 970 and GTX 980 have 4GB VRAM (Video Ram), some users over the past few weeks have been reporting weird or horrible performance while the GPU is using higher than 3.5GB.
This seems to occur because Nvidia and all their wisdom decided that they would add the 3.5GB as one memory pool and then add a second memory pool of 500MB.
It seems like there is some communication issues between the two which causes this issue, on top of this memory configuration some games only read the 3.5GB pool of Ram. An example of this would be Sleeping Dogs and Middle-Earth: Shadow of Mordor but the latter seems to have fixed that quite recently. Essentially the issue is when trying to use above 3.5GB VRAM the GPU starts to chug in performance.
Nvidia commented on the issue.
“The GeForce GTX 970 is equipped with 4GB of dedicated graphics memory. However the 970 has a different configuration of SMs than the 980, and fewer crossbar resources to the memory system. To optimally manage memory traffic in this configuration, we segment graphics memory into a 3.5GB section and a 0.5GB section. The GPU has higher priority access to the 3.5GB section. When a game needs less than 3.5GB of video memory per draw command then it will only access the first partition, and 3rd party applications that measure memory usage will report 3.5GB of memory in use on GTX 970, but may report more for GTX 980 if there is more memory used by other commands. When a game requires more than 3.5GB of memory then we use both segments”.
“We understand there have been some questions about how the GTX 970 will perform when it accesses the 0.5GB memory segment. The best way to test that is to look at game performance. Compare a GTX 980 to a 970 on a game that uses less than 3.5GB. Then turn up the settings so the game needs more than 3.5GB and compare 980 and 970 performance again”.
The following graph is benchmark results using less than 3.5GB and above 3.5GB, graph sourced from PCPer.
“On GTX 980, Shadows of Mordor drops about 24% on GTX 980 and 25% on GTX 970, a 1% difference. On Battlefield 4, the drop is 47% on GTX 980 and 50% on GTX 970, a 3% difference. On CoD: AW, the drop is 41% on GTX 980 and 44% on GTX 970, a 3% difference. As you can see, there is very little change in the performance of the GTX 970 relative to GTX 980 on these games when it is using the 0.5GB segment”.
I wont pretend I fully understand the issue from the component perspective but maybe these other sources can.