The issue has been known and widely discussed in online forums. Nvidia markets the chip as having 4GB of video RAM, but some users have identified that the chip falters after using 3.5GB of that allocation.
The lawsuit says the remaining half gigabyte runs 80 percent slower than it's supposed to. That can cause images to stutter on a high resolution screen and some games to perform poorly, the suit says.
Nvidia has responded to the issue, saying that the GTX 970 uses a different memory subsystem design than its higher-end GTX 980, and that the difference has a negligible impact on performance. It has also said that, due to an error, the original specifications it published for the GTX 970 were incorrect.
The suit was filed in the U.S. District Court for Northern California and names as defendants Nvidia and Giga-Byte Technology, which sells the GTX 970 in graphics cards.