copied from technotes here
Video Mode Resolution and Color Depth
CGA 320 x 200 with 4 colors
640 x 200 with 2 colors
EGA 640 x 350 with 16 colors from a palette of 64 colors (text mode)
640 x 200 with 2 colors (graphics mode)
VGA 640 x 480
SVGA 640 x 480, 800 x 600, 1024x 768 and higher with X colors from a palette of 16.7 million color.
(X depends on the amount of video ram, ranges from 256 - 16.7 million)
VRAM or Video RAM is dual ported (it can be read to and written from at the same time). Although VRAM is fast, it is not as fast as WRAM.
WRAM or Windows Accelerator Card RAM is faster than VRAM, and thus produces better video than VRAM. WRAM is also dual ported, meaning it can be both read from and written to at the same time.
SGRAM or Synchronous Graphic RAM synchronizes with the CPU bus. SGRAM uses masked writes and blocked writes in order to increase bandwidth for intensive graphics. SGRAM is not dual ported, and cannot be read to and written from at the same time, although it can open two memory pages at once.