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

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

  • Comments 44

 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.


  • 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.
  • 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! :-)
  • Steve,
    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.
  • 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.
  • You're right j, I got the numbers wrong :(.
  • Wasn't there a version of NT for PowerPC as well? I thought it ran on the RS/6000 43p?
  • 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...
  • In case you don't know, links your weblog to their main page.
  • 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) how did DOS 5 then 6 come about? Sorry if this is answered elsewhere, haven't poked around yet.
  • 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.
  • So there are two different products called DOS 4? One regular version and one "amazing" version? Clear as mud.
  • Is Dos 4.0 and 4.1 freewhare now, if so, whare can i download it? Also, is Xenix still sold?
  • I guess nobody believed what John Christian stated in his <a href="">Curriculum Vitae</a> until today. You have done something good for him! ;-)
  • Sorry for the ugly link. I though you were supporting tags.
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