Mode 13h

Mode 13h is an IBM VGA BIOS mode. It is the specific standard 256-color mode on IBM's VGA graphics hardware. It features a resolution of 320×200 pixels. It was used extensively in computer games and art/animation software of the late 1980s and early to mid-1990s. Since the earlier CGA and EGA graphics standards provided a similar resolution mode, its use simplified conversions to those formats.

Mode 13h provided programmers with a straightforward manner of accessing video memory (nicknamed chunky graphics), at the expense of not being able to access other useful features of the VGA hardware.

Given the aspect ratio of a 320×200 resolution screen for use on a 4:3 display, Mode 13h does not have square pixels.

Mode 13h is something of a curiosity, because the VGA is a planar device from a hardware perspective, and not suited to chunky graphics operation. The VGA has 256 KiB of video memory consisting of 4 banks of 64 KiB, known as planes (or 'maps' in IBM's documentation). Planar memory arrangement splits the pixels horizontally into groups of four. For any given byte in the PC's 64 KiB video memory aperture, four pixels can be accessed on screen by selecting the required plane(s). This is more complicated for the programmer, but allows access to all of the available video memory and other benefits (see Mode X).

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