Mode 13h
VGA's simplest graphics mode: 320×200 pixels in 256 colours with one byte per pixel in a flat memory buffer.
IBM shipped the mode with the VGA card in 1987. One byte per pixel in contiguous memory from segment A000h made drawing trivial: write a value, get a coloured dot. That was enough for most DOS games and early PC demos, and the 256 colours could be chosen freely from a palette of 262,144 shades. The catch is that only 64 KB is visible at once, with no hardware page flipping and no easy double buffering — exactly what Mode X fixes by unlocking the whole card's memory.