Mode X is a 320 × 240 256-color graphics display mode of the VGA graphics hardware for IBM PC compatibles. It was first publicized by Michael Abrash in his July 1991 "Ramblings in Realtime" column in Dr. Dobb's Journal. The articles were reprinted in chapters 47-49 of Abrash's Graphics Programming Black Book. The term "Mode X" was coined by Abrash. Mode X is a variant of the 320 × 200 Mode 13h with the resolution increased to 320 × 240, giving square pixels instead of the slightly elongated pixels of Mode 13h. It is enabled by entering Mode 13h via a BIOS system call, then changing the values of several VGA registers.