INT 10H

The BIOS typically sets up a real mode interrupt handler at this vector that provides video services.

Such services include setting the video mode, character and string output, and graphics primitives (reading and writing pixels in graphics mode).

INT 10h is fairly slow, so many programs bypass this BIOS routine and access the display hardware directly.

Setting the video mode, which is done infrequently, can be accomplished by using the BIOS, while drawing graphics on the screen in a game needs to be done quickly, so direct access to video RAM is more appropriate than making a BIOS call for every pixel.

AL = video mode (For Old IBM Only) Normally a character cell has 8 scan lines, 0–7.