If you're running your PC in 1600 by 1200 resolution, with 32 bit colour, then that's a total of 61,440,000 bits for the whole display. Which is 7,680,000 bytes, which is 7,500 kilobytes, which is about 7.32 megabytes. It's not 7.5 megabytes, because there are 1024 bytes in a kilobyte and 1024 kilobytes in a megabyte. This is something that marketing people conveniently forget when they're telling you how big hard drives are. But I digress.
If you're using "double buffering" (more informatively referred to as
page flipping) - and, today, you almost certainly are - then that doubles this memory requirement. Double buffering renders the upcoming frame into another area of memory from the frame buffer, so the incoming data doesn't affect the currently-displayed frame.
Even at 1600 by 1200, though, 16Mb is still plenty for double buffered 2D video. Heck, it's enough for
triple buffering, if you drop your resolution to 1280 by 960.
Full Scene Anti-Aliasing (
FSAA) can eat a lot more memory. Basically, all flavours of FSAA render more pixels than they have to, and then average them out to give a final image with smoother diagonal edges. Jaggy diagonals look bad enough in still frames; they look even worse when there's animation going on, causing the stair-steps to "crawl" up and down the lines.
FSAA doesn't change the amount of memory needed for the final display buffer or its double- or triple-buffered cousins, but it adds yet another buffer, for the intermediate higher resolution data, that's two or four times as big as any of the others.
But, assuming 2X FSAA and double buffering, we still haven't used up all of the memory on a humble 32Mb video card.
All of the
rest of the modern graphics card memory budget is taken up by 3D data.
