Apple DOS
Apple DOS refers to
operating systems for the
Apple II series of
microcomputers from
1978 through early
1983. Also known simply as
DOS 3.x, 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 DOS 3.2 did that minor release receive its own version number, DOS 3.2.1. The best-known and most-used version is DOS 3.3 in the
1980 and
1983 releases. Prior to the release of DOS 3.1, Apple users had had to rely on audio cassette tapes for data storage and retrieval, but that method was notoriously slow, inconvenient and unreliable.
DOS 1 and DOS 2 were purely internal development versions; DOS 3.0 was never publicly released either as it had some remaining bugs. Apple DOS was largely written by
Steve Wozniak, Randy Wigginton, and outside contractor Paul Laughton and was closely tied to the
Integer BASIC programming language. It lacked any sort of official documentation from
Apple, much to the dismay of many programmers, until release 3.2.
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 at that point. A second bug-fix release came afterwards, addressing a problem with its MASTER.CREATE
computer program, used to create more DOS disks.
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 could boot a disk 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; 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 DOS 3.1 or 3.2 when the computer was running DOS 3.3. To counteract this problem, Apple Computer released a utility called "MUFFIN" to migrate DOS 3.2 files and programs to DOS 3.3. To migrate DOS 3.3 files in the reverse direction, back to DOS 3.2, users came up with a "NIFFUM" utility, but Apple Computer never officially supported transfers in that direction. DOS 3.3 also improved ability to switch between the old Integer BASIC and the newer AppleSoft BASIC if the user had a "Language Card" memory expansion.
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Beneath Apple DOS was a popular guide to Apple DOS. |
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, unlock, rename, and verify a file's 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 accepts a startup program (usually HELLO). On top of the File Manager, the Main DOS Routine were implemented which hooked into the machine's BASIC interpreter and intercepted all disk commands. It provided BLOAD, BSAVE, and BRUN for loading and running binary executables. LOAD, RUN, and SAVE were provided for running BASIC programs, and a EXEC was provided for running text files as BASIC programs. 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 basic programs).
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 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 didn't like its much higher memory footprint) continued using Apple DOS or one of its
clones long after 1983. The Apple convention to store 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.
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.
* ISBN 0-912985-00-3
*
Paul Laughton's account of writing DOS 3.1*
Apple II History: DOS*
A2Central.com – Apple II news and downloads
*
comp.sys.apple2 – (
Usenet newsgroup) – most active free Apple II user forum
*
Everything2.com's DOS 3.1 Article
