GeForce GTX 970 cards may have memory problem
The GeForce GTX 970 is a really nice high-end video card but according to numerous reports on the Internet the card has a memory problem – it cannot efficiently access some of the memory installed.
Most GTX 970 models come with 4 GB of GDDR5 memory installed and while 3 GB of the memory is accessed normally (read at full speed and with insane memory bandwidth) the upper 1 GB offers much lower speed. The problem is best seen in games and applications that use the entire on-board memory – if you stay below 3 GB or in some cases below 3.3 GB or 3.5 GB everything is fine, if you go above then you will experience lower performance. This problem is currently not seen in the faster GeForce GTX 980 model.
NVIDIA has responded to the news by saying that the memory subsystem of the GTX 970 works differently compared to the memory subsystem of the GTX 980 – the memory of the GTX 970 is divided into two chunks with the first one being 3.5 GB and the second one being 0.5 GB. This is due to the fact that the GTX 970 has a different configuration of SMs and fewer crossbar resources to the memory. Thus the GPU happens to have higher priority access to the 3.5 GB partition, while the 0.5 GB chunk is not as important and hence as fast. Moreover NVIDIA has tested the two video cards in both <3.5 GB and >3.5 GB modes and has not found extraordinary performance degradation. In a few words – everything is OK, folks. Then again there are some opinions online that suggest NVIDIA may fix this issue with a new driver or even with new GTX 970 microcode.
Source: The Tech Report