The function of VRAM is to "store image data that the computer displays; it acts as a buffer between the CPU and the video card. When a picture is to be displayed on the screen, the image is first read by the processor and then written to the VRAM."

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Video Random Acess Memory

From my personal experience, I do not believe there is too much of a performance impact. It depends on how much vram is needed and how much you have. And sometimes it depends on how the engine handles textures. For example, if a game requires around 1.5GB (Average) of VRam for textures, and your GPU has only 1GB, you should be fine.

Furthermore, If you are only off by a little, it is not a big deal. But if the game requires 1.5GB or so of VRam, and you only have 256MB of VRam, then you are going to be seeing some issues.

If you are suffering from performance issues, do not first assume it is the Vram, as it could just be the GPU itself. I find people usually claiming the Vram to be the culprit of bad performance, even if the person is off by just a little.

From this, I conclude that you can be missing around .5GB (512MB) of Vram, and you won't notice too much of an issue.

VRAM is to GPU as RAM is to CPU.

VRAM is basically video memory that's installed on the same board as the GPU in your video/graphics card. When you load up a game, it's responsible for storing texture and graphical data that requires to be rendered and be displayed on your monitor.

In the case of integrated GPUs, some may use your physical RAM that's also being used by the CPU as VRAM instead.