Did you know that OS/2 wasn’t Microsoft’s first non Unix multi-tasking operating system?

 Most people know about Microsoft’s official timeline for its operating-system like products

1.      Xenix - Microsoft’s first operating system, which was a version of UNIX that we did for microprocessors. 

2.      MS-DOS/PC-DOS, a 16 bit operating system for the 8086 CPU

3.      Windows (not really an operating system, but it belongs in the timeline).

4.      OS/2, a 16 bit operating system written in joint development with IBM.

5.      Windows NT, a 32 bit operating system for the Intel i386 processor, the Mips R8800 and the DEC Alpha

But most people don’t know about Microsoft’s other multitasking operating system, MS-DOS 4.0 (not to be confused with PC-DOS 4.0)

MS-DOS 4.0 was actually a version of MS-DOS 2.0 that was written in parallel with MS-DOS 3.x (DOS 3.x shipped while DOS 4 was under development, which is why it skipped a version).

DOS 4 was a preemptive real-mode multitasking operating system for the 8086 family of processors.  It had a boatload of cool features, including movable and discardable code segments, movable data segments (the Windows memory manager was a version of the DOS 4 memory manager).  It had the ability to switch screens dynamically – it would capture the foreground screen contents, save it away and switch to a new window.

Bottom line: DOS 4 was an amazing product.  In fact, for many years (up until Windows NT was stable), one of the DOS 4 developers continued to use DOS 4 on his desktop machine as his only operating system.

We really wanted to turn DOS 4 into a commercial version of DOS, but...   Microsoft at the time was a 100% OEM shop – we didn’t sell operating systems, we sold operating systems to hardware vendors who sold operating systems with their hardware.  And in general the way the market worked in 1985 was that no computer manufacturer was interested in a version of DOS if IBM wasn’t interested.  And IBM wasn’t interested in DOS.  They liked the idea of multitasking however, and they were very interested in working with that – in fact, one of their major new products was a product called “TopView”, which was a character mode window manager much like Windows.  The wanted an operating system that had most of the capabilities of DOS 4, but that ran in protected mode on the 286 processor.  So IBM and Microsoft formed the Joint Development Program that shared development resources between the two companies.  And the DOS 4 team went on to be the core of Microsoft’s OS/2 team.

But what about DOS 4?  It turns out that there WERE a couple of OEMs that had bought DOS 4, and Microsoft was contractually required to provide the operating system to them.  So a skeleton crew was left behind to work on DOS and to finish it to the point where the existing DOS OEM’s were satisfied with it.


Edit: To fix the title which somehow got messed up.


Comments (42)
  1. Anonymous says:

    Wasn’t MS-DOS / PC-DOS also a joint deal with IBM?

  2. Anonymous says:

    Did you just make this up, or did you read something someone else had just made up?

  3. Anonymous says:

    see http://www.acad.humberc.on.ca/~frig8279/osessay/dos/history

    or just search google for "history of dos"

  4. Anonymous says:


    "Did you just make this up, or did you read something someone else had just made up?"

    So, you know Mr. Osterman has worked for Microsoft since the mid-80’s right? And that he started there, on the DOS 4 project? You might want to check his bio.

  5. Anonymous says:

    Is there anywhere to get a copy of this nowadays?

  6. Anonymous says:


    Feh. The story is uncorroberated BS.

    Didn’t see any mention of working for MS on his site, and you’d certainly think he’d of mentioned this in his ‘article.’ Feh. The story is uncorroberated BS.

  7. Anonymous says:

    pjm, Actually I have worked at Microsoft since 1984. Here’s my bio from the first post: http://weblogs.asp.net/exchange/articles/85057.aspx

    The timeline you quoted above is the official timeline, it doesn’t include either multitasking MS-DOS 4.0 or multitasking MS-DOS 4.1. But they did exist, primarily for the OEMs that had contracted it. I couldn’t find a reference for the Goupil contract, but here’s a reference to DOS 4.1 which was done for ICL: http://www.presentd.demon.co.uk/linear-cv.html

    Just because you’re not familiar with a product doesn’t mean that it doesn’t exist.

    Louis: Actually the relationship between MS-DOS and PC-DOS is somewhat complicated. I’ll try to write about that tomorrow.

  8. Anonymous says:

    I have Xenix.

    I also have a *manual* for DOS 4.0.

    When DOS 3.1 came out for the AT, I heard about the task switching stuff, ( that the DOS 5.0 shell did ), and had my friend get me a maunal from Daharan. No software, but I did get the manual. Later, DOS 5.0 had the features.

  9. Anonymous says:

    I have a vague memory of using this. It would have been in 1988 when I was working at STL for the summer – STL was the research part of STC (who owned ICL and was later taken over by Nortel ). Some of the ICL PCs at STL had a multitasking DOS4 on them.

  10. Anonymous says:

    I used MS-DOS 4.0 as a kid in Hong Kong in the late 80’s when/where piracy was thriving. There’s a computer shopping centre called Golden and I remember there were about 20 shops sharing the same OEM copy of MS-DOS 4.0!

  11. Anonymous says:

    if i remember correctly, Apricot also had this version of DOS as an OEM product, they were later taken over by Mitsubishi

  12. Anonymous says:

    I remember that Microsoft was kind of annoyed/surprised when IBM shipped PC DOS 4.0. IIRC the main reason/feature for/of IBM’s DOS 4.0 was the >32MB partition support.

    Digital Research had a multi-user version of their CP/M-86. In 1989 we used a multi-user DOS clone made by a another American company, which I don’t remember anymore. We used it for a dial-in server with about 4 modems.

  13. Anonymous says:

    LSN WebLog » Did you know that OS/2 wasn’t Microsoft’s first non Unix multi-tasking operating system?

  14. Anonymous says:

    I have MS-DOS 4.01, but for sure is the one that in reality is 9.x right?

  15. Anonymous says:

    3.x excuse me 🙂

  16. Anonymous says:

    Hmmm…..anyone else run a multi-tasking, multi-line BBS under Qemm/DESQview? By the way, 4DOS was the Command shell of choice for that beauty. There was an amazing power under DOS in that environment.

    I wouldn’t be surprised at what MS had hidden in a box, given that most of the stuff we used Qemm ‘stealth’, etc….all ended up absorbed by MS or Symantec.

  17. Anonymous says:

    Yep I ran a multi-line BBS using Qemm/Desqview. I remember thinking how cool it was to be able to run two programs at one time! 🙂

  18. Anonymous says:


    My guess is that you used the Microsoft version of PC-DOS 4.0 instead of multitasking MS-DOS 4.0 – Multitasking DOS 4.0 was only delivered to Goupil in France to my knowledge, It’d surprise me immensely if it made it outside there.

  19. Anonymous says:

    You mention that NT ran on the MIPS R8800 which never existed, the NT kernel was developed on R3000 and R4000 before being ported to other architectures.

  20. Anonymous says:

    You’re right j, I got the numbers wrong :(.

  21. Anonymous says:

    Wasn’t there a version of NT for PowerPC as well? I thought it ran on the RS/6000 43p?

  22. Anonymous says:

    Sure, that was NT 3.51. But my listing above was in operating system families, not the specific versions of the various operating systems – I’d almost certainly get it wrong so…

  23. Anonymous says:

    In case you don’t know, osnews.com links your weblog to their main page.


  24. Anonymous says:

    The way you write it sounds like Microsoft more or less decided to quit developing DOS and work on OS/2 (and then of course Windows), and just finished up a "DOS 4.0" to fulfill a contract (I remember the DOS 4 that shipped as an appallingly buggy piece of crap)…so how did DOS 5 then 6 come about? Sorry if this is answered elsewhere, haven’t poked around yet.

  25. Anonymous says:

    Nope, there was parallel development.

    The product known as multi-tasking MS-DOS 4.0 lived on as OS/2, while the product known as MS-DOS 3.1 continued on in parallel through DOS 3.2, DOS 3.3, DOS 4.0, DOS 5.0 and DOS 6.0.

  26. Anonymous says:

    So there are two different products called DOS 4? One regular version and one "amazing" version? Clear as mud.

  27. Anonymous says:

    Is Dos 4.0 and 4.1 freewhare now, if so, whare can i download it? Also, is Xenix still sold?

  28. Anonymous says:

    I guess nobody believed what John Christian stated in his <a href="http://www.presentd.demon.co.uk/linear-cv.html">Curriculum Vitae</a> until today. You have done something good for him! 😉

  29. Anonymous says:

    Sorry for the ugly link. I though you were supporting tags.

  30. Anonymous says:

    I had a dodgy crap version of DOS 4.0, That DOS version was the first with "MEMMAKER". I upgraded from DOS 3.3, to DOS 4.0 and then to DOS 5.0.

    You can download DOS 6.0 -> DOS 6.22 from MS MSDN site. I think I still have DOS 4.0 Disks floating around somewhere.

    BTW, I ended up ditching DOS altogether and Used OS/2 2.1, which ran my Windows 3.x apps faster than Win3x did.

  31. Anonymous says:

    Sorry, I also have SCO’s version of Xenix with MS Word for Xenix.

    MMMM. Imaging Windows like Mac OS X, Win on Unix. That would be great.

  32. Anonymous says:

    Why use an acient architecture? I’d prefer BeOS approach of a complete rewrite.

  33. Anonymous says:

    An ancient architecture?

    Um. We’re talking about 1984 here. It wasn’t ancient back then.

    BeOS is a much more recent vintage OS and it had the advantage of a processor that had virtual memory protection.

    NT WAS a complete rewrite with a modern architecture.

  34. Anonymous says:

    I remember being somewhat amazed when PCDOS4.0 shipped, certainly the guys from MS UK who I’d bump into at trade shows (I worked for Borland at the time) all knew about the multi-tasking MSDOS4 since it went to ICL for OEM use so I thought the naming was terrible.

    I seem to remember being told that the multi-tasking was limited to one task that had the screen & keyboard with other tasks being limited in functionality, I didn’t realise you could use it swap the foreground task around.

  35. Anonymous says:

    You’re 99.9% accurate Peter, I’m impressed that anyone remembered 🙂

    The version of DOS that ICL used didn’t have screen swapping – that functionality was there but not exposed on the ICL machines because they didn’t require it. When the DOS 4 project was modified for the remaining customers, we removed a bunch of stuff that they weren’t interested in, including the screen swapping stuff.

  36. Anonymous says:

    Can we download MS-Dos now ?

  37. Anonymous says:

    Not to my knowledge.

    Just because a product has reached it’s End-of-life for support doesn’t mean that Microsoft’s going to make it available all of a sudden for free.

    And it would be an absolute support nightmare to have an MS-DOS download – DOS requires machines have floppy disks, but many computers (including the one I’m writing on right now) don’t have them.

  38. Anonymous says:

    where can i download OS/2. is there aby freeware or shareware available

  39. Anonymous says:

    if there is, can share it to me at miranda_abonzo@yaho.com my email

    thank you very much



  40. Anonymous says:

    If you want OS/2, download eComStaion on ur fav p2p.

    os/2 warp 4 is a little harder to find (all the version floating around are german or dutch) but it can be found, and so can advanced server.

    Workers of the world unite!

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