Those phosphors light up to produce colored dots, or pixels . Basically, it's the ability to move lots of pixels with many colors at high speed. To accomplish this, modern boards incorporate video co-processors , or accelerators, which take the video work away from your computer's main processor. Instead of figuring out where to put each dot on the screen, your processor passes the work along to the video board, which frees up the main processor to do other things. Good video boards contain a substantial amount of memory to store screen images.
More memory enables a video board to produce higher- resolution images with more colors.
Most video adapters let you choose how much you want of each. The higher the resolution and color depth, the better the picture. Unfortunately, as image quality goes up, speed usually goes down. The best boards will provide the highest quality image with the fewest compromises in performance. This is the number of horizontal and vertical pixels the video board produces, expressed in terms of counts.