Work orders between a developer and Steve Jobs show how the Apple II OS was built, along with schematics from Steve Wozniak and the the final operating system code.
Origins of Apple's DOS code
SANTA CRUZ MOUNTAINS, Calif. -- Without a disk drive, the Apple II might never have become one of the most iconic computers in history. But Apple desperately needed a disk operating system to run its hard drives. Newly surfaced documents illustrate the process that led to the creation of that DOS.
Communications between Apple's Steve Jobs and developer Robert Shepardson discuss the components of the Apple II disk operating system, including a file manager, a BASIC and Applesoft BASIC interface, and disk copying, recovery, and backup utilities.