A Brief History of Computing
- Operating Systems

Development of MS-DOS/PC-DOS began. Microsoft (known mainly for their programming languages) were commissioned to write the Operating System for the PC, Digital Research failed to get the contract (there is much legend as to the real reason for this). DR's Operating System, CP/M-86 was later shipped but it was actually easier to adapter older CP/M programs to DOS rather than CP/M-86, and CP/M-86 cost $495. As Microsoft didn't have an operating system to sell they bought Seattle Computer Product's 86-DOS which had been written by Tim Paterson earlier that year (86-DOS was also know as Q-DOS, Quick & Dirty Operating System, it was a more-or-less 16bit version of CP/M). The rights were actually bought in July 1981. It is reputed that IBM found over 300 bugs in the code when they subjected the operating system to their testing, and re-wrote much of the code.

Tim Paterson's DOS 1.0 was 4000 lines of assembler.

MS-DOS 1.0., PC-DOS 1.0.

Microsoft (known mainly for their programming languages) were commissioned by IBM to write the operating system, they bought a program called 86-DOS from Tim Paterson which was loosely based on CP/M 80. The final program from Microsoft was marketed by IBM as PC-DOS and by Microsoft as MS-DOS, collaboration on subsequent versions continued until version 5.0 in 1991.

Compared to modern versions of DOS version 1 was very basic, the most notable difference was the presence of just 1 directory, the root directory, on each disk. Subdirectories were not supported until version 2.0 (March, 1983).

MS-DOS (and PC-DOS) was the main operating system for all IBM-PC compatible computers until 1995 when Windows '95 began to take over the market, and Microsoft turned its back on MS-DOS (leaving MS-DOS 6.22 from 1993 as the last version written - although the DOS Shell in Windows '95 calls itself MS-DOS version 7.0, and has some improved features like long filename support). According to Microsoft, in 1994, MS-DOS was running on some 100 million computers world-wide.

This version was the first to support 3½" disks, although only the 720KB ones. Version 3.2 remained the standard version until 1987 when version 3.3 was released with the IBM PS/2.

Version 3.4 - 4.x are confusing due to lack of correlation between IBM & Microsoft and also the USA & Europe. Several 'Internal Use only' versions were also produced.

This version reflected increases in hardware capabilities, it supported hard drives greater than 32 MB (up to 2 GB) and also EMS memory.

This version was not properly tested and was bug ridden, causing system crashes and loss of data. The original release was IBM's, but Microsoft's version 4.0 (in October) was no better and version 4.01 was released (in November) to correct this, then version 4.01a (in April 1989) as a further improvement. However many people could not trust this and reverted to version 3.3 while they waited for the complete re-write (version 5 - 3 years later). Beta's of Microsoft's version 4.0 were apparently shipped as early as '86 & '87.

In order to promote OS/2 Bill Gates took every opportunity after its release to say 'DOS is dead', however the development of DOS 5.0 lead to the permanent dropping of OS/2 development.

This version, after the mess of version 4, was properly tested through the distribution of Beta versions to over 7,500 users. This version included the ability to load device drivers and TSR programs above the 640KB boundary (into UMBs and the HMA), freeing more RAM for programs. This version marked the end of collaboration between Microsoft and IBM on DOS.

Hello everybody out there using minix-
I'm doing a (free) operating system (just a hobby, won't be
big and professional like gnu) for 386(486) AT clones.

In 1992, the GNU project (http://www.gnu.org/) adopted the Linux kernel for use on GNU systems while they waited for the development of their own (Hurd) kernel to be completed. The GNU project's aim is to provide a complete and free UNIX like operating system, combining the Linux or Hurd platform with the a complete suite of free software to run on it. In order to allow it to carry the GNU name, the Linux kernel copyright was changed to the GNU Public License Agreement (http://www.gnu.org/copyleft/gpl.html) on the 1st of February 1992.

MS-DOS 6.0. This included a Hard-Disk compression program called DoubleSpace, but a small computing company called 'Stac' claimed that DoubleSpace was partly a copy of their Compression Program, Stacker. After paying damages Microsoft withdrew DoubleSpace from MS-DOS 6.2, releasing a new program - DriveSpace - with MS-DOS version 6.22. In operation and programming interface DriveSpace remains virtually identical to DoubleSpace. MS-DOS 6.22 remains the last version of MS-DOS released, since Microsoft turned its efforts to Windows '95. Windows '95 (and later) DOS shell reports itself as DOS 7 - and includes a few enhancements, e.g. support for long filenames.