NVIDIA explains why GTX 970 cannot use its full 4GB VRAM
 

Owners of the new NVIDIA GTX 970 graphics card have been complaining that it doesn’t seem to be using any more than 3.5GB of available memory when playing games at Quad-HD or 4K resolutions, which is lower than the 4GB of VRAM that NVIDIA claimed the card comes with. NVIDIA mentions in the official spec-sheet...

http://vr-zone.com/articles/nvidia-e...ram/86055.html