Display: 320x400

The IBM VGA standard has a 320x200 mode that allows for up to 256 colors. There are other VGA modes that allow 400 scan lines, 640x400, for example. But these do not allow for 256 colors due mainly because to memory constraints. But, because of several successive choices in the progression from MDA, CGA, to MCGA (each using 200 scan lines in popular modes), apparently, IBM chose have 400 scan lines as the standard in all VGA modes. Conveniently double the 200 scan lines of previous standards. The result is, 320x200 is not actually 200 scan lines, it is 400. But each scan line is repeated to fill the 400 scan lines by default when mode 13h (320x200x256) is activated. But by flipping some registers and loading graphics into the proper memory locations, the line doubling is switched off and the hardware looks at different memory locations to fill every other line. The result is an effective 320x400x256 with a negligible number of clock cycles added to each frame.