Apple DOS

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Template:Infobox OS Image:Beneathappledos.jpg

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.

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. 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. DOS 3.1 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. DOS 3.1 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.

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 oficially 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.

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.

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