Apple DOS

Apple DOS is a disk operating system from Apple, which was used in the Apple II computers. Usually simply called the Apple DOS area, it is still not to be confused with the better-known MS -DOS. Was succeeded by the end of 1983 the more versatile Apple ProDOS, which was not in much of Apple DOS, but Apple SOS, the operating system of the failed Apple III, modeled.


The Apple II was launched in spring 1977. First, the conventional Compact Cassette served as a storage medium by a standard cassette recorder is connected via its microphone and headphone jacks on the Apple; This storage method was necessary because of the modulation sound signals in slow, uncomfortable by the manual operation and due to the system unreliable and impractical for multipart programs. So recognized Steve Wozniak and Steve Jobs that a drive for floppy disks would be important for the development of their computer. At that time only a few years previously invented floppy disk drives in the microcomputer area even more expensive luxury for many computer models were not available.

In order to control a floppy disk drive, the Disk II later, Wozniak designed the design of the Disk II hardware and the necessary operating system Apple DOS ( Disk Operating System Apple ). The hardware-related routines of DOS for controlling the drive motors as well as for the conversion of the GCR data stream into individual sectors of data (and vice versa ), he wrote himself, the routines for the file system were awarded as a commission. The Apple DOS was loaded during system start with a very simple boot loader that was in the ROM of the drive controller from a floppy disk. It integrated itself into the Apple Integer Basic, which was stored in the read only memory of the computer.


The DOS versions 0.x, 1.x, 2.x and 3.0 were unpublished trials; the first public Apple DOS was version 3.1 in July 1978. Approximately half a year later appeared DOS 3.2 (which is the new Apple II supported and a large number of bugs removed ), and shortly thereafter DOS 3.2.1 (another bugfix version). The most common Apple DOS 3.3 DOS version is dated August, 1980, increased the amount of space per disk from 113 to 140 KB by effectively brought by an improved GCR coding 16 instead of 13 sectors on each track disks. After that, Apple turned to the Apple III, so about two and a half years, no new DOS for the Apple II appeared more, though continued to exist a number of known bugs in the DOS code; in particular the APPEND command often did not work properly.

During this time, however, some highly accelerated Apple DOS versions from other vendors released. This replaced the ineffective GCR-Codierung/Decodierung the original version in which the data repeatedly copied in memory and were not written to the disk by an optimized version, which already completed much of the necessary work during the writing / reading. Known DOS versions of this period are, inter alia, ProntoDOS, Davidos and ES- DOS.

After the disastrous failure of the Apple III in the market, Apple turned back to the still well-running Apple II series; it appeared in January and August 1983 with two error-corrected and better adapted to the new Apple IIe, but still slow versions of Apple DOS, both still wore the version number 3.3, but can be recognized in the annual statement 1983 in the startup message. The version of August 1983, however, the message is still in the start " January 1983 " spent, was also the last marketed under the name Apple DOS operating system, and the only one in which the APPEND command actually worked flawlessly.

Source publication

2013, 35 years after the Apple II publication, the Apple DOS source code from the Computer History Museum and its website has been published. Paul Laughton, the programmer had made ​​him available.

Technical limitations

Apple DOS supported in unmodified form any storage media except 5.25-inch floppy disks, was not very far-reaching changes unsuitable for disks with more than 400 KB capacity, and offered no subdirectories. His system less defined file types was too inflexible for many purposes. In addition, there was a lack of documented programming interface for DOS for machine-language programs, because Apple DOS was entirely designed for BASIC programs out. Therefore, the development has not been as larger media such as hard drives and 3.5 -inch floppy disks were affordable.