NVIDIA now has responded to the findings:

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 3^rdparty 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.

http://www.guru3d.com/news-story/does-the-geforce-gtx-970-have-a-memory-allocation-bug.html

요약: GTX970은 980에서 몇 개의 SMM이 잘려나간 프로세서이기 때문에 VRAM에 접근하는 방식이 다르다. 첫 3.5GB를 먼저 사용하고, 게임 등의 어플리케이션이 꼭 사용해야 하는 경우에 마지막 .5G도 사용하기 시작한다

요약2: GTX970 = 208bit / GTX980 = 256bit

그러니까 탑재된건 4GB GDDR5 VRAM이지만 실질적으로 일부분밖에 효율적으로 사용 할 수 없는

208bit 카드를 256bit 카드로 속여팔고 있다는 얘기가 되네요?

970으로 게임에서 뚝뚝 끊기는 현상이 일어나시는 분들 참고하시면 좋을 것 같습니다