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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?

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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.


  • 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.
  • 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.
  • Why use an acient architecture? I'd prefer BeOS approach of a complete rewrite.
  • 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.
  • 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.
  • 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.
  • Can we download MS-Dos now ?
  • 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.
  • where can i download OS/2. is there aby freeware or shareware available
  • if there is, can share it to me at my email

    thank you very much

  • 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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