Nvidia has a couple of video cards, the GTX 70 and the GTX80. Looking at them from a glance, one would think that the GTX80 would provide higher performance and better performance. Well and good.
But the model in the limelight is actually the GTX70, which for some reason, has reportedly providing unusual VRAM allocation and bandwidth. To be more precise, the GTX70 was allocating less of its available memory than expected.
Both cards do have 4GB on board but the GTX70 does not max out to the full 4GB. Techies discovered that it could only go as much as 3.5GB with the remaining 512 GB available in certain instances but at lower transfer rates.
So of course, unlike the GTX80, one would think that the GTX70 could have a flaw. However, such is not the case according to Nvidia. And to prove their claim, an official release was brought out to explain why the GTX970 performed that way.
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.
Nvidia Senior VP Jonah Alben further explained that the GT970 is working like it was designed to and that the said unusual behavior is due to the Maxwell-class GPUs. However he does admit that the company faltered a bit in properly communicating the GPU specs to reviewers, since it does take advantage of Maxwell's ability to disable selectively a portion of L2 cache.
As it turns out, Alben believes that the GTX970 is working as designed and that their goal was achieved. Hence, it seems that everything was a misunderstanding as far as properly relaying the specs and explaining them altogether.
Hopefully the technically sane people would feel the same way.
Here is a video explaining the features of the GeForce GTX980 and 970 to give you a better overview.
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