The game was first released in 1985 on a self-booting disk that supported CGA, PCjr, and Tandy graphic cards (as opposed to "King's Quest I", which had separate versions for all three) in 1985 as a disk that booted on start-up. Sierra included several modifications to the AGI engine for compatibility with the IBM AT and EGA cards, which had been introduced since King's Quest I was released. The copy protection used on King's Quest I proved to be incompatible with the AT BIOS, so a different scheme was used. Color palette selection in CGA mode was changed to utilize the BIOS instead of modifying the palette register directly. The game engine was also changed to utilize the PC's timer chip instead of a CPU-based speed loop which would result in the game running too fast on the AT.