OS/2 Versions And History
This is a list, chronologically sorted, of OS/2 versions, related products, and historic dates.
IBM PC DOS 3.1 (1984)
Multitasking DOS 4
Officially called just MS-DOS 4.00, Multitasking DOS 4 was the intended successor of DOS 3.x, developed some time before 1985. It has many features later appearing in both OS/2 and Windows, like the New Executable format, system calls using dynamically linked functions instead of interrupts, the concept of processes along with related system calls, and the use of a higher-level language (C) for writing parts of the operating system. However, unlike any version of OS/2 released to the public (TODO: check for 1986 ADOS 5.0), both earlier MS-DOS COM and MZ executables and MS-DOS interrupts are supported on Multitasking DOS 4.
This version of DOS supports pre-emptive multitasking, but its usability is limited by the 640kB memory limit, with no swapping because of lack of necessary hardware support. For this reason, it was only released to certain OEMs, opting to wait with the public release for its protected mode successor[1].
Preserved Copies
There are two versions of Multitasking DOS 4 that were preserved. The first one is a two-floppy set, originally uploaded to the now defunct JSMachines.net website. It does not contain any branding and its kernel (IBMDOS.COM) identifies itself as internal revision 6.7, 85/11/26, which is consistent with the creation date of the files. The internal revision identification is cut off with an end of string sign, possibly indicating it was manually edited after the build; together with the fact IBM branding is used, it hints that this is actually a pre-release version. Floppy 1 contains the operating system and a few basic utilities, including FDISK and FORMAT; floppy 2 contains additional utilities, commands, a copy of the 8086 New Executable linker (LINK4.EXE), a PIF editor (PIFEDIT.EXE), and EDLIN.
The second version is an OEM release by SMT Goupil, a French company, for their Goupil G4 computer, featuring an 80186 clocked at 8 MHz. It was originally a two-floppy set, but the only preserved version is a single 720kB floppy. Based on timestamps, it was built on 15 May 1986, and possibly assembled into a single floppy on 20 March 1997. The kernel is renamed to MSDOS.SYS and IO.SYS, like it is common on MS-DOS (strings inside IO.SYS reveal the source was still named IBMBIO.ASM), and the internal revision string is not present. In addition to what is the first version, it contains a Unix-like PS.EXE utility, revealing some internals about the OS, a kernel debugger (DEBUGDD.SYS), a networking driver (NET.SYS), and DOSSIZE.EXE, an utility printing used and available memory. Strangely, the session manager (SM.EXE) is missing[2].
Tips and Tricks
TODO: How to install Multitasking DOS 4, how to run DOS applications (adjusting memory limits with MEMSET).
Development
No toolchain directly targeting Multitasking DOS 4 was preserved, however, the aforementioned distributions contain a linker. An effort to combine it with Microsoft C is happing on DisNCord.
OS/2 Pre-Betas
These need to be sorted by date