320x200x256 was the only 256-color mode available through the standard VGA BIOS. aka "mode 13" because it's mode 0x13 on interrupt 0x10, subfunction 0.
is one byte, there is only one bit plane
. All of the pixels fit in 64k at one time thus bit planes and page switching
This mode was popular for it's ease of programming and its plethora of colors, but the low resolution was a severe limitation. It was probably intended for use in games that require lots of color/images and very little text.
320x200 does not fit the standard 4:3 aspect ratio, so pixels are not square and circles become ellipses.