Larry Osterman's WebLog

Confessions of an Old Fogey
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 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.


  • Wasn't MS-DOS / PC-DOS also a joint deal with IBM?
  • Did you just make this up, or did you read something someone else had just made up?
  • see

    or just search google for "history of dos"
  • @pjm
    "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.
  • Is there anywhere to get a copy of this nowadays?
  • @engmar

    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.
  • pjm, Actually I have worked at Microsoft since 1984. Here's my bio from the first post:

    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:

    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.
  • 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.
  • 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.
  • 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!
  • if i remember correctly, Apricot also had this version of DOS as an OEM product, they were later taken over by Mitsubishi
  • 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.
  • LSN WebLog &raquo; Did you know that OS/2 wasn&#8217;t Microsoft&#8217;s first non Unix multi-tasking operating system?
  • I have MS-DOS 4.01, but for sure is the one that in reality is 9.x right?
  • 3.x excuse me :)
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