Apple DOS 3.1, which was the first operating system for any Apple computer, was released in 1978 for the Apple II computer. DOS 3.0 was never publicly released as it had some remaining bugs. DOS 3.1 was largely written by Steve Wozniak, Randy Wigginton, and outside contractor Paul Laughton. DOS 3.1 was largely tied to the Integer BASIC programming language. DOS 3.1 lacked any sort of official documentation from Apple, much to the dismay of many programmers.
Apple DOS 3.2 was released in 1979 to reflect major changes in computer booting methods that were built into the successor of the Apple II, the Apple II Plus. Instead of the original Integer BASIC, the newer AppleSoft BASIC was written into the ROM of the II+. Also, the new ROM had an updated computer reset function, which started automatically when the II+ was powered up.
Apple DOS 3.3 was released in 1980. DOS 3.3 improved various functions of DOS 3.2, while also allowing for large gains in available floppy disk storage. Unfortunately, this had the side effect of making it difficult to read disks formatted in DOS 3.2 . DOS 3.3 also improved ability to switch between the old Integer BASIC and the newer AppleSoft BASIC. DOS 3.3 could only read floppy disks running in a Disk II disk drive and could not access hard disk drives, virtual RAM drives, or 3.5-inch floppy disk drives.