Mode 13h

Mode 13h provides programmers with a linear 320 × 200 block of video memory, where each byte represents one pixel.

[2] 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.

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).

The color palette data is not stored in memory per se, but rather modified, read and written to by low level I/O port calls, to the DAC registers.

Due to the way chunks of memory are allocated in such an environment, the bytes in segment 0xA000 from offset 64000 to 64768, can be written to with no negative effects.

In x86 assembly language the mode is entered when AL is 13h, AH is 0 and BIOS INT 10h is executed.

[1] However, the "h" is sometimes dropped for languages that don't support that method of notation; for example, it is known as screen mode 13 in QuickBASIC and its spinoffs.