Q. What do you mean by Video Memory ?

As declared before video memory is also entitled framebuffer since it buffers video frames to be displayed. The quality of a video display relies a lot on how quickly can the framebuffer be accessed and be updated by video system.  In early video systems video memory was just a fixed area of system RAM. Afterwards there was video RAM that came with video cards themselves and could be increased by putting additional video RAM under UMA (Unified Memory Architecture). Video RAM is again part of system RAM. UMA is what you get in modern low-cost motherboards with on-board video and sound cards etc. 

Amount of video memory necessary is dependent on resolution and colour-depth required of the system.  Let's see how to calculate amount of video memory required. The video memory required is simply the resolution (which means the total number of pixels) multiplied by Colour Depth.