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DOS

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Description

The IBM Personal Computer Disk Operating System or PC-DOS, more commonly known as just DOS, is a fairly rudimentary operating system originally shipped with the IBM PC in 1981, primarily a CP/M clone with some facilities modified for a more "IBM like" behaviour or to conform to IBM naming conventions (config.sys etc.). DOS is also a subsytem of OS/2, running in cohabitation with version 1.x and as a task in version 2 and later, and a collective name for a variety of operating systems that offer compatibility with the PC-DOS system to varying degrees.

Version 1 was so buggy it was rewritten mostly from scratch by IBM and Microsoft, which is the reason all subsequent DOS releases from Microsoft contain an IBM copyright notice, the manual for DOS was also an internal IBM product and not written by either MicroSoft or SCP.

Porting issues

Since we have a few given facts such as:

  • OS/2 command line was developed with compatibility with DOS in mind
  • OS/2 has support for all known DOS codepages
  • OS/2 has a DOS subsystem that is a full version of DOS v5 built in

It is somewhat apparent that porting to and especially from DOS is as easy as it gets, if you cannot get the tools or the time to make a 32 bit version for OS/2, you can in a worst case scenario run the original program under the DOS subsystem. Most plain text mode tools port with little or no changes, primarily you will have to keep note of integer and floating point values since a 32 bit system will respond differently than a 16 bit one, and there are minor API differences, not every last DOS call has a 100% equivalent in OS/2.

Problems can happen when you are dealing with applications that call windowing libraries and other GUI or graphic libraries, the most common libraries actually got ports to OS/2 but there remain a few reasonably common libs that never gained an OS/2 version and it may be difficult to get hold of some of the others now. If you have the source for the graphic library however you may be in luck since the OS/2 command line actually supports most of the graphic modes that DOS has and therefore porting them is relatively simple.

The only other issue to keep in mind when porting is that old software sometimes has artificial limits built into them or assumptions made that made sense at the time they were written but not today. Installers and other programs that query disk sizes in 16 bit values made sense when disk came in 5 to 30 megabyte sizes, dates were also commonly calculated using small integers from a set date (typically 1980), this meant that the integer value ran out around 2007, some programs assumed only 2 digits for a year which is OK if you are only calculating something that needs current dates such as a PIM, but not good for historical data, some assumed that the program would run in the 20th century only so if they are run now they think it is 1915, so on and so forth.

Development tools like Clipper and dBase for instance supported four digit years out of the box but programmers writing in those two languages commonly just used the last two of the date field when calculating values, this is not a difficult fix but can get a bit time consuming.

Porting tools

  • Clipper/dBase/xBase: Harbour (Current) - X2C (Discontinued) - XHarbour (Discontiued) - XBase++ (Discontinued) | All are Clipper style compilers, no-one has been making dBase like interpreted products for a while.
  • Basic:
  • C/C++:
  • Modula-2: All M2 for OS/2 vendors provided TopSpeed Modula-2 compatibility packages for their products, but in all cases as separate downloads and not as part of the main package.
  • Prolog:
  • Pascal: Most OS/2 Pascal vendors offered some sort of Turbo Pascal compatibility, the open source Free Pascal is actually a TP clone.

Known versions

This lists major versions of DOS, minor versions such as 6.21 or 6.22 that are product specific upgrades or minor bug fix releases are not listed unless they have some specific significance.

  • DOS Plus
  • DR-DOS v5
  • DR-DOS v8
  • DR-DOS v8.1
  • Enhanced DR-DOS 7.01.08
aka EDR-DOS
  • FreeDOS 1.1 (Current)
  • MS-DOS v1
  • MS-DOS v1.1
  • MS-DOS v2
  • MS-DOS v3
  • MS-DOS v3.3
  • MS-DOS v4
  • MS-DOS v5
  • MS-DOS v6
  • MS-DOS v6.2
  • MS-DOS v7
  • MS-DOS v8 (Current)
  • OpenDOS v7.01
  • PC-DOS v1
  • PC-DOS v1.1
  • PC-DOS v1.25
  • PC-DOS v2
  • PC-DOS v3
  • PC-DOS v3.2
  • PC-DOS v3.3
  • PC-DOS v5
  • PC-DOS v6
  • PC-DOS v6.1
  • PC-DOS v6.3
  • PC-DOS v7
  • PC-DOS 2000
  • PC-DOS v7.1 (Current)
  • PTS-DOS 32

Authors

Links

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