Apple DOS

Infobox_OS
name = Apple DOS


caption =
developer = Apple Computer
family = Apple DOS
version_number = Varies
source_model = Closed source
working_state = Historic
latest_release_version = 3.3
latest_release_date = 1980 (last released bug fix in 1983)
kernel_type = Monolithic kernel
license = Apple Software License Agreement
website =

Apple DOS refers to operating systems for the Apple II series of microcomputers from 1979 through early 1983. Apple DOS had three major releases: DOS 3.1, DOS 3.2, and DOS 3.3; each one of these three releases was followed by a second, minor "bug-fix" release, but only in the case of Apple DOS 3.2 did that minor release receive its own version number, Apple DOS 3.2.1. The best-known and most-used version was Apple DOS 3.3 in the 1980 and 1983 releases. Prior to the release of Apple DOS 3.1, Apple users had to rely on audio cassette tapes for data storage and retrieval, but that method was notoriously slow, inconvenient and unreliable.

Version history

Apple DOS was largely written by Steve Wozniak, Randy Wigginton, and outside contractor Paul Laughton. It was closely tied to the Integer BASIC programming language. To the dismay of many programmers, Apple published no official documentation until release 3.2.

Apple DOS 1 and 2 were purely internal development versions; Apple DOS 3.0 was never publicly released because of remaining bugs. Apple DOS 3.1, which was the first disk-based operating system for any Apple computer, was released in June 1978 for the Apple II, which had been on the market for a little less than one year. A second bug-fix release came afterwards, addressing a problem with its MASTER CREATE utility, which was used to create Apple DOS master disks. (The built-in INIT command created disks that could be booted only on machines with the same amount of memory as the one that had created them. MASTER CREATE included a self-relocating version of DOS that would boot on Apples with any memory configuration.)

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, dubbed Autostart, which could boot a disk automatically when the II+ was powered up.

Apple DOS 3.3 was released in 1980. It improved various functions of release 3.2, while also allowing for large gains in available floppy disk storage; the newer P5A/P6A PROMs in the disk controller could read and write data at a higher density, so that instead of 13 sectors, 16 sectors of data could be stored per disk track, increasing the capacity to 140 KB per disk side, with about 130KB available for user programs. Unfortunately, this had the side effect of making it difficult to read disks formatted in prior versions. To counteract this problem, Apple Computer released a utility called "MUFFIN" to migrate Apple DOS 3.2 files and programs to version 3.3. To migrate Apple DOS 3.3 files in the reverse direction, back to version 3.2, users came up with a "NIFFUM" utility; Apple never officially supported transfers in that direction. Release 3.3 also improved the ability to switch between the old Integer BASIC and the newer Applesoft BASIC, if the computer had a language card memory expansion.

Technical details

Apple DOS 3.1 disks used 13 sectors of data per disk track, each sector being 256 bytes in size. It used 35 tracks per disk side, and could access only one side of the floppy disk, unless the user flipped the disk over. This gave the user a total storage capacity of 113.75 KB per disk side, of which about 10 KB were used to store DOS itself and the disk directory, leaving about 100KB for user programs.

Compared to the modern operating systems of today, Apple DOS was quite primitive. The first layer of the operating system was called the RWTS, which stands for "read/write track sector". This layer consisted of subroutines for track seeking, sector reading and writing, and a disk formatting. An API called the File Manager was built on top of this, and implemented functions to open, close, read, write, delete, lock (i.e. write-protect), unlock (i.e. write-enable), and rename files, and to verify a file's structural integrity. There is also a catalog function, for listing files on the diskette, and an init function, which formats a disk for use with DOS, and stores a startup program (usually called HELLO) that will be auto-started when this disk is booted. On top of the File Manager API, the main DOS routines were implemented which hooked into the machine's BASIC interpreter and intercepted all disk commands. It provided BLOAD, BSAVE, and BRUN for storing, loading and running binary executables. LOAD, RUN, and SAVE were provided for BASIC programs, and an EXEC was provided for running text-based batch files consisting of BASIC and DOS commands. Finally, 4 types of files existed, identified by letters in a catalog listing.

Apple DOS File Formats:
* I: Integer BASIC programs (stored in a compact format, not plain-text).
* A: AppleSoft BASIC programs (also stored in a packed, space-saving format).
* B: Binary files, either executable machine-language programs, or data files.
* T: ASCII text files (or plain-text, unpacked batch files).

There were four additional file types; 'R', 'S' and an additional 'A' and 'B', none of which were fully supported. DOS recognized these types for catalog listings only, and there were no direct ways to manipulate these types of files. The 'R' type found some use for relocatable binary executable files. A few programs supported the 'S' type as data files.

Decline of Apple DOS

After 1980, DOS entered into a state of stagnation, along with all other Apple II products, as Apple concentrated its efforts on the ill-fated Apple III computer and its SOS operating system. After the Apple III had been abandoned by the company, two more versions of Apple DOS, both still called DOS 3.3 but with some bug fixes and better support for the new Apple IIe model, were released in early and mid 1983.

Without third-party patches, Apple DOS could only read floppy disks running in a 5.25-inch Disk II disk drive and could not access any other media, such as hard disk drives, virtual RAM drives, or 3.5-inch floppy disk drives. The structure of DOS was such that it was not possible to have more than 400 KB available per drive without a major rewrite of almost all sections of the code; this was the main reason Apple abandoned DOS in 1983, when Apple DOS was entirely replaced by ProDOS.

ProDOS retained the 16-sector low-level format of DOS 3.3 for 5.25 inch disks, but introduced a new high-level format that was suitable for devices up to 32 MB in size; this made it suitable for hard disks and 3.5-inch floppies. All the Apple computers from the Apple II Plus onward can run both DOS 3.3 and ProDOS, the Apple II Plus requiring a "Language Card" memory expansion to use ProDOS; the Apple //e and later models had built-in Language Card hardware, and so could run ProDOS out of the box. ProDOS included software to copy files from Apple DOS disks. However many people who had no need for the improvements of ProDOS (and who did not like its much higher memory footprint) continued using Apple DOS or one of its clones long after 1983. The Apple convention of storing a bootable OS on every single floppy disk meant that commercial software could be used no matter what OS the user owned. A program called DOS.MASTER enables users to have multiple virtual DOS 3.3 partitions on a larger ProDOS volume, which allowed the use of many floppy-based DOS programs with a hard disk.

Apple stopped authorizing user groups to distribute DOS 3.3 many years ago, but granted one company, Syndicomm, an exclusive license to resell DOS 3.3.

References

* ISBN 0-912985-00-3

External links

* [http://www.laughton.com/Apple/Apple.html Paul Laughton's account of writing DOS 3.1]
* [http://apple2history.org/history/ah14.html Apple II History: DOS]
* [http://www.a2central.com/ A2Central.com] — Apple II news and downloads
* [http://everything2.net/index.pl?node_id=1177572 Everything2.com's DOS 3.1 Article]