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DOS: A history by the numbers

86-DOS

In 1979 Seattle Computer Products (SCP) had developed a 8086-based computer. It would run Microsoft's Stand-Alone Disk BASIC. It would run an 8086 version of CP/M -- whenever Digital Research got around to writing it. Unfortunately, DR kept pushing back the release date. SCP could not sell their computer until it had an operating system. They didn't want to wait around with no income while DR got its act together so SCP employee Tim Paterson created an OS for SCP in two-man months. It was initially dubbed QDOS for Quick and Dirty Operating system. It came with assembly language development utilities. Unfortunately, there was no editor. Paterson spent another week hacking together something he called EDLIN. He figured the whole shebang, QDOS and EDLIN, would last about six months until DR cranked out the 8086 version of CP/M.

Time passed and still no 8086 CP/M appeared. Oh dear. SCP decided an update of QDOS was in the offing. Its new version, released December 1980, was renamed 86-DOS. Microsoft, as everyone knows, was casting about for an operating system and purchased the rights to 86-DOS for $50,000.

Interestingly enough, part of the deal SCP signed with Microsoft was that SCP could, in perpetuity, sell computers with MS-DOS royalty free ("all updates, enhancements and versions"). It seemed no biggy at the time. SCP wasn't exactly a national operation. MS wasn't going to lose much money on the 100 machines SCP sold per year. This wasn't IBM or Zenith, after all. However, SCP decided this unique licensing deal made themselves valuable if they sold themselves to a national computer maker. Being able to sell a PC clone with a free operating system would give the PC maker a significant price advantage. SCP's contract was pure gold. SCP approached Microsoft and told them they were going to do just that, offer themselves for sale to a national computer maker. Microsoft, of course, could buy them first for about $20 million. Microsoft balked. Gates raged the contract was nontransferable and was only good for computers with 8086 processors. He refused to honor the contract. SCP pointed out there was no clause in the contract indicating the deal was nontransferable or the OS could only be preinstalled on 8086 systems. Microsoft soon found itself in court facing a $60 million lawsuit.

Microsoft's defense was the deal was for versions based on DOS 1.0, not the post-2.0 rewrite. SCP's attorney Kelly Corr likened the contract to a deal that every year gave a person the pick of the litter. He noted Microsoft was not so much claiming the person could no longer have the pick of the litter but Microsoft was claiming the animal had changed entirely. The jury, grossly unfamiliar in the early '80s with things like computer operating systems, sided with the Corr's folksy analogy. Microsoft ended up settling with SCP to purchase all rights to DOS for slightly less than $1 million.

DOS 1.1

Microsoft released this update to DOS 1.0 May 1982. It fixed a number of bugs in DOS 1.0. Its major enhancement was support for 320KB double-sided floppy disk drives. Previous to DOS 1.1, double-sided floppies were only usable by turning the disk over to the other side. An OEM version for a Zenith PC was released as DOS 1.25 (aka Z-DOS).

COMMAND.COM is 4,959 bytes in size.

DOS 2.0/2.01/2.1/2.11

DOS 2.0 was a complete rewrite of the DOS 1.1 code. It was released in March 1983. It was created to address IBM's new line of XT computers. DOS 2.0 supported hard drives. It could address up to a 15 mb drive (XTs shipped with 10 mb drives). DOS 2.0 was patterned more after UNIX, getting away from its CP/M roots. Microsoft doubled the number of commands DOS could perform. DOS 2.0 added support for subdirectories. It also allowed installable device drivers and I/O redirection (i.e., commands like <tt>ls > file.txt</tt>). A 2.1 version was released November 1983 to support IBM's PC Jr. In the same month, a 2.01 OEM version was released to support a Wang Computer Corporation PC. Finally, in December 1983, Microsoft released DOS 2.11 which added support for extended character sets and some rudimentary I18N support like foreign characters and alternative date formats.

COMMAND.COM is 17,792 bytes in size.

DOS 3.0

In September 1984 Microsoft released DOS 3.0 to support IBM's AT line and Intel's 80286 chip. Support for 1.2 mb floppy drives was added as well as the AT's 16-bit ISA slots. DOS 3.0 also supported hard disks up to 32 mb in size. Rudimentary LAN support was added, but it mostly didn't work.

COMMAND.COM is 22,042 bytes in size.

DOS 3.1

Microsoft released DOS 3.1 in November 1984. It was chiefly released to support businesses that wanted to connect PCs to LANs. Microsoft's solution was adding something called the Network Redirector to DOS 3.1. It allowed one to access a network as a drive letter, instead of having to use special software to transfer files between the PC and the server.

COMMAND.COM is 23,210 bytes in size.

DOS 3.2

Microsoft released DOS 3.2 in December 1985. It supported 3.5" 720Kb Floppy drives. This was the first version Microsoft sold directly to consumers. All previous versions came preinstalled by the OEM. DOS 3.2 was the standard for a long time (until 1987 with the release of DOS 3.3). The IBM OEM version of DOS 3.2 (as opposed to the Microsoft general release of DOS 3.2) had an odd bug. It would not read floppies formatted with non-IBM DOS versions (versions previous to 3.2)! The IBM OEM version looked for IBM's copyright notice on track 0. If it didn't find it, you'd get the message: "File allocation table bad, drive A". Many speculated this was an intentional bug... anti-competitive practices on the part of IBM. Microsoft, it seems, learned at the feet of the master.

COMMAND.COM is 23,612 bytes in size.

DOS 3.3

Microsoft released DOS 3.3 in April 1987. It was released to support IBM's new PS/2 series as well as 3.5" 1.44 mb floppies. DOS 3.3 further enhanced I18N (supporting some 17 languages) and added support for the CMOS system clock. DOS 3.3 could address hard disks up to 32 MB. DOS 3.3 added the FDISK command, allowing users to partition hard drives bigger than 32 MB. Previous to FDISK, users had to buy third-party software to partition and read larger drives.

DOS 3.3 became the gold-standard of DOS ... the DOS people ran back to after the disastrous releases of DOS 4.0.

Digital Research got into the DOS game at this time, releasing DR-DOS 3.31 (there were no 3.0-3.2 versions). Some viewed it as a better DOS than DOS. Some versions of DR-DOS were also bundled with the GEM Desktop system. Some called that a better Windows than Windows.

COMMAND.COM is 25,276 bytes in size.

DOS 4.0

Microsoft released DOS 4.0 in July 1988. It was the super-buggy follow on to DOS 3.3. DOS 4.0 was supposed to allow EMS to access up to 8Mb of RAM and support 2 GB hard disks. Unfortunately, the bugs drove many users to return to DOS 3.3. Microsoft was working on OS/2 at the time as well as its own Windows line, so it's likely Microsoft did not allocate proper resources. Microsoft released a DOS 4.01 (November 1988) but most users sat pat until DOS 5.0.

DOS 4.0 introduced the first MS DOS shell interface. DOS 4.01 was the first version to support Russian Cyrillic characters. The few people that actually slogged through with 4.01 were offered an upgrade to a 4.01A release in April 1989. The A version supported larger hard drives.

There's a theory that, due to the public outcry over DOS 4.0, MS has developed a superstition about naming anything 4.0 anymore. For example, it wasn't Windows 4.0, it was Windows 95.

COMMAND.COM is 37,254 bytes in size.

DOS 5.0

By the time Microsoft released DOS 5.0 in April 1991, it had learned something about software testing in the intervening three years. DOS 5.0 went through the largest beta testing in history (up until that time).

DOS 5.0 could now load itself in high memory area (HMA). It allowed device drivers and TSRs to load themselves in the upper memory area (UMA).

DOS 5.0 added the undelete utility and a disk cache utility (which ended up causing Microsoft a new set of problems). It added the SETVER command. Lots of programs checked to see what DOS version was running before running. Earlier versions of DOS had major backward compatibility problems and programmers had to check DOS versions before running. Short sighted programmers, for some reason, never envisioned DOS 5.0. Programs perfectly compatible would not run.

Microsoft replaced GW-BASIC with QBASIC. It added the delightful DOSKEY command.

DOS 5.0 also added man pages for its commands.

COMMAND.COM is 47,987 bytes in size.

DOS 6.0/6.2/6.21/6.22

Microsoft released DOS 6.0 in August 1993. Although a full revision number, it's questionable whether DOS 6.0 justified a revision from 5.0 to 6.0. There were rumors DOS 6.0 would be a full 32-bit DOS but those proved groundless. It's likely Microsoft called it DOS 6.0 instead of DOS 5.1 or 5.5 because Digital Research had released DR-DOS 6.0.

DOS 6.0 incorporated a lot of utilities that previously had been the domain and cash cow of third-party software makers. DOS 6.0 added a virus scanning utility and featured a command called MEMAKER which took a lot of the guess work out of editing your AUTOEXEC.BAT and CONFIG.SYS. A couple new file commands were added. DELTREE now let you delete an entire group of folders and files. MOVE let you move a file to a different directory. Previously, you had to COPY a file and then DELETE the old file.

The most controversial addition was Microsoft's DoubleSpace utility. Microsoft had for a while been negotiating a take over of Stac Electronics, maker of the STACKER disk compression utility. After the deal fell apart, Microsoft did what it typically did if you don't sell your software company to Microsoft for Bill-favorable terms. MS threw 200 programmers on a project to create their own version. Microsoft's version DoubleSpace was released with DOS 6.0. Even before DOS 6.0's actual release, Stac launched a lawsuit.

The Stac lawsuit wasn't the only problem DoubleSpace was causing Microsoft. Users were complaining the utility was eating files. Microsoft released DOS 6.2 in November 1993 to address these concerns. DOS 6.2 included DoubleGuard, which ensured memory wasn't corrupted before writing data to the disk. It also included ScanDisk to scan and repair disk errors. Finally, DOS 6.2 gave users the ability to decompress their hard drive, should they decide DoubleSpace was more trouble than it was worth.

In February 1994, a court ruled Microsoft had illegally used Stac's disk compression algorithm. MS was ordered to pay Stac $120 million. However, Microsoft launched a counter-suit against Stac. A court found Stac too had misappropriated Microsoft "preload" technology. Stac was ordered to pay Microsoft $13.7 million. (It's interesting to note that Stac made in a year what Microsoft made in 4 hours.)

To comply with the court order, Microsoft had to release DOS 6.21 in March 1994, which was essentially DOS 6.2 sans any form of disk compression. As well, Microsoft was required to make reasonable efforts to recall all version of DOS 6.x that featured the compression. Cha ching!

Before the recall was to take effect, Microsoft and Stac surprised the computer world by announcing a cross-licensing deal. Both agreed to not pursue the court awards. Microsoft would pay Stac a licensing fee of $1 million a month for 43 months and buy $40 million worth of Stac stock.

Microsoft eventually released DOS 6.22 in April 1994 with new disk compression software called DriveSpace. Although Microsoft had a licensing deal with Stac, DriveSpace used a public-domain compression algorithm.

COMMAND.COM is 52,925 bytes in size.

-- Karl Mamer

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