music. Custom disk routines allowed Ultima IV to have faster disk access than the previous games, which was also important as the growing size of the game caused it to now use two floppy disks instead of one. The dialog of two NPCs in the Apple II release were accidentally not entered, leaving them in their default test states. One of these NPCs was the most elusive in the game, and provided the player with the final answer they would require to complete the game. With this character not responding properly, players were forced to guess the correct answer or find it from sources outside the game to complete it. This bug would later be acknowledged in Ultima V, where the NPC appears again and admits his mistake to the player. Commodore 64 The Commodore 64 port was the first in the series to take full advantage of the computer's hardware rather than simply converting the sound and graphics from the Apple II, and include in-game music. It came on two 1541 disks and like the Apple II, Side 1 of Disk 1 (labeled "Program") was copy protected while the other disk sides ("Overworld", "Town", and "Dungeon") were not and the user was instructed to make backups of them. Ultima IV also added support for two disk drives, in which case the user would keep the Overworld side of Disk 1 in Drive 0 and flip the Town/Dungeon disk as needed in Drive 1. The Overworld disk is also used to load/save the player's progress. One of the biggest criticisms of the C64 port was a lack of any disk fast loader, which made for extremely slow disk access against the speed-optimized disk routines in the Apple version. Atari 8-bit Ultima IV was the final game in the series ported to the Atari 8-bit family. The game is still designed to support a 48K Atari 800 even though four models of 64K/128K Atari 8-bit computers had been released, and one 64K-upgradable model, starting two and a half years earlier. In order to fit the game in 48K, the Atari 8-bit version cut out music support. The reason 48K was made the requirement instead of the 64K requirement of the Apple II version is that, whereas the earliest Apple II models were upgradable to 64K, the Atari 400/800 were only officially upgradable to 48K. Since the Apple version was programmed to