Apple DOS

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Apple DOS
Apple DOS.png
developer Apple computer
License (s) Proprietary
Current  version 3.3 (August 1983)
Architecture (s) Apple II
Others Language: English

Apple DOS (Apple Disk Operating System) is a diskette operating system released by Apple in 1978 that was used on Apple II computers. In the Apple context, it was mostly simply called DOS (similar to MS-DOS on IBM PC-compatible computers ). The successor at the end of 1983 was the more versatile Apple ProDOS , which was largely based not on Apple DOS, but on Apple SOS , the operating system of the failed Apple III.


The Apple II was launched in the spring of 1977. Initially, the conventional compact cassette served as a storage medium by connecting a standard cassette recorder to the Apple via the microphone and headphone sockets; This storage method was slow because of the necessary modulation into audio signals, inconvenient to operate, unreliable due to the system and hardly practicable for multi-part programs. So Steve Wozniak and Steve Jobs realized that a floppy disk drive would become important in the development of their computers . At that time, the floppy disk drives in the microcomputer sector, invented only a few years earlier, were still an expensive luxury and not available at all for many computer models.

In order to be able to control a floppy disk drive, the later Disk II , Wozniak designed the hardware and the corresponding software Apple DOS. He wrote the hardware-related routines of the DOS for controlling the drive motors and for converting the GCR data stream into individual data sectors (and vice versa), the routines for the file system were assigned as commissioned work. When the system was started, Apple DOS was loaded from a floppy disk using a simple boot loader located in the read-only memory (ROM) of the drive controller. It integrated into the Apple Integer Basic that was stored in the computer's ROM.


DOS versions 0.x, 1.x, 2.x, and 3.0 were unreleased trial versions; the first public Apple DOS was version 3.1 from July 1978. About six months later, DOS 3.2 appeared, which supported the new Apple II + and fixed a large number of program errors; shortly afterwards DOS 3.2.1, another bug-fixed edition. The most widespread Apple version is DOS 3.3 from August 1980, which increased the storage space per diskette from 113 to 140 kB by using an improved GCR coding to accommodate 16 instead of 13 sectors on each diskette track. After that, Apple turned to the Apple III , so that no new DOS appeared for the Apple II for over two and a half years, although a number of known bugs in the DOS code continued to exist; in particular, the APPEND command often did not work properly.

During this time, some highly accelerated third-party Apple DOS versions appeared . These replaced the ineffective GCR coding of the original version, in which the data was copied several times in the memory and only then written to the floppy disk, with an optimized version that did a large part of the necessary work while writing or reading. Known DOS versions of this period include a. ProntoDOS , DaviDOS and ES-DOS .

After the failure of the Apple III, Apple turned back to the Apple II series, which continued to do well. In January and August 1983 two corrected and better adapted to the new Apple IIe , but still slow, versions of Apple DOS appeared. Both still had the version number 3.3, but can be recognized by the year 1983 in the start message. The version from August 1983, which still output "January 1983" in the start message, was also the last operating system sold under the name Apple DOS , and the only one in which the APPEND command worked without errors.

Source code publication

In 2013, 35 years after the Apple II release, the Apple DOS source code was published by the Computer History Museum and its website. Paul Laughton, the programmer, had made it available.

Technical restrictions

Apple DOS did not support any storage media other than 5.25-inch floppy disks, was unsuitable for storage media with a capacity of more than 400 kB without extensive changes  and did not offer any subdirectories . His system of less defined file types was too inflexible for many purposes. In addition, there was a lack of a documented programming interface to DOS for machine language programs, since Apple DOS was designed entirely for BASIC programs. Therefore, the further development was stopped when larger data carriers such as hard drives and 3.5-inch floppy disks became affordable.

See also

Other computers using Apple DOS

Apple DOS was usually used as reprogramming, by other computer manufacturers as an operating system, such as from from Bulgaria coming Prawetz 8D , in turn, a clone of the Oric Atmos is.


Web links

Individual evidence

  1. Len Shustek: Apple II DOS source code ( English ) November 12, 2013. Retrieved November 30, 2013.
  2. Apple II's 35-year-old operating system is now open to the public ( English ) November 13, 2013. Retrieved November 30, 2013.