Monday, January 26th 2015
The GeForce GTX 970 memory allocation bug discovery, made towards last Friday, wrecked some NVIDIA engineers' weekends, who composed a response to what they tell is a non-issue. A bug was discovered in the way GeForce GTX 970 was allocating its 4 GB of video memory, giving some power-users the impression that the GPU isn't addressing the last 700-500 MB of its memory. NVIDIA, in its response, explained that the GPU is fully capable of addressing its 4 GB, but does so in an unusual way. Without further ado, the statement.
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.Continued
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.
Here's an example of some performance data:
|Shadow of Mordor|
|<3.5GB setting = 2688x1512 Very High||72 fps||60 fps|
|>3.5GB setting = 3456x1944||55fps (-24%)||45fps (-25%)|
|<3.5GB setting = 3840x2160 2xMSAA||36 fps||30 fps|
|>3.5GB setting = 3840x2160 135% res||19fps (-47%)||15fps (-50%)|
|Call of Duty: Advanced Warfare|
|<3.5GB setting = 3840x2160 FSMAA T2x, Supersampling off||82 fps||71 fps|
|<3.5GB setting = >3.5GB setting = 3840x2160 FSMAA T2x, Supersampling on||48fps (-41%)||40fps (-44%)|
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.Source: The TechReport