Before OS/2 was named OS/2 by IBM on April 2, 1987, the operating system was known by many different names at Microsoft as it evolved, including DOS5, MT-DOS, CP-DOS, and ADOS.

In late 1986, Microsoft began working on a couple different branches. One was called SIZZLE, where a variety of performance improvements were tested before being merged back into the main branch.

Another branch was FOOTBALL (aka PIGSKIN), an early 80386-based prototype intended to test the viability of the running multiple DOS applications in V86-mode. Sometimes this 80386 version was also called 386DOS, to distinguish it from 286DOS. More details are in this FOOTBALL Design Document.

To shed some light on those efforts, I recently added a few OS/2 Prototype Disks: a small collection of early (mostly pre-1.0) OS/2 boot disks that provide a glimpse of what some of those early OS/2 builds looked like.

Getting these early versions of OS/2 to run in PCjs has been a bit of a challenge. There have been some successes but also some lingering issues. Debugging continues.

Part of the problem is that these pre-1.0 builds still contain a few bugs. Also, the original OS/2 FOOTBALL Boot Disk from February 1987 was developed and tested exclusively on Compaq DeskPro 386 machines from late 1986, so it has some uncommon 80386 dependencies:

  • The 80386 LOADALL instruction
  • 32-bit segment register writes must modify only 16 bits of memory

FOOTBALL also had some specific video hardware requirements: CGA or EGA. Note that the VGA, which is what most emulators use by default these days, did not exist in 1986. The VGA was introduced in April 1987, when IBM unveiled their new PS/2 hardware line – and announced OS/2.

January 23, 2016