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Thread: Probably the dumbest question...

  1. #1

    Default Probably the dumbest question...

    This is probably the dumbest, most blasphemous question ever seen in the TRS-80 forum:

    But, I must ask. Can you run MS-DOS on 5 1/4" floppys on a TRS-80?

    Let the tomato throwing begin!

  2. #2


    Short answer is no.

    The Z80 CPU in the TRS80 is an extension of the earlier Intel 8080 processor. The instruction set is fully compatible with the 8080; however it had additional instructions and a different register set which made it 'more powerful'.

    MS-DOS was specifically written for an Intel 8088/8086 processor. These processors are also an evolution of the 8080; however they did not go down the same 'additional instructions' and 'different register set' like the Z80. As such software like MS-DOS written for the 8086/8088 family will not work on a Z80. Furthermore the hardware behind the CPU is totally different in a PC vs the TRS80. The TRS80 is very primitive in comparison as it was designed to be an affordable computer for home and business. The IBM PC architecture was designed primarily for business; thus it was complex and very expensive in comparison. MS-DOS makes extensive use of this hardware (i.e. timers, memory arrangement, graphics etc).

    Have a read on Wikipedia about the Z80, Intel 8080 and 8086/8088. You will soon see the differences.
    Last edited by 3pcedev; January 16th, 2016 at 11:21 AM.

  3. #3


    I had figured as much.

    Thank you for taking the time to give a detailed answer. I really appreciate it!

  4. #4
    Join Date
    May 2009
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    Trick answer is yes. The Tandy 2000 was officially badged with a TRS-80 logo and could run MS-DOS.

    I think there was a IBM PC on a card add-on for the Model 3/4 but I can't find an online reference for it.

    If you really want to go crazy, write an emulator that allows the Z-80 to run 808x code which would allow you to run MS-DOS. Then you could load a CP/M-86 emulator for MS-DOS and load a CP/M-80 emulator for CP/M-86 and have the ultimate in crazy looping code. This would be quite slow though.

    What exactly are you trying to do?

  5. #5


    Quote Originally Posted by ardsleytank View Post
    Can you run MS-DOS on 5 1/4" floppys on a TRS-80?
    Yes, but only on a TRS-80 that looks like this:

    IMG_0396.jpgIMG_0396 (2).jpg

    The TRS-80 Model 2000 was followed by the Tandy 1000, Tandy 3000, etc., and then the Model 2000 became known as the "Tandy 2000", but it was officially a TRS-80, as you can see it says right there on the tin.

  6. #6


    Krebizfan- Nothing yet. I don't have a TRS-80 yet, but when looking for TRS-80 system disks I noticed the plethora of 5 1/4" MS-DOS Disk sets.

    However, just a minute ago, I discovered that CP/M and MS-DOS have VERY similar qualities, so I might just go with that.

    Petrofsky- Very helpful, I've never heard of a 2000!

  7. #7


    Quote Originally Posted by krebizfan View Post
    I think there was a IBM PC on a card add-on for the Model 3/4 but I can't find an online reference for it.
    That would be a hell of a trick. I think you're thinking of the opposite: a Model 3/4 compatibility card that plugged into a PC. That would have been quite feasible, and Radio Shack apparently started to develop one but never released it. See

  8. #8


    There was one other way to run MS-DOS on a TRS-80. Maybe. In 1983, Veritas Technology released an 8088 Dual Processor Option (DPO) board for the Model II/12/16. The design was similar to the MC68000 board found in the Model 16 in that it was a complete 8088 system running in tandem with the Z80 system for I/O support. There are a few magazine articles about it, with a detailed review in Advanced Computing (aka two/sixteen) magazine from Jan/Feb 1984 where it was successfully tested with CP/M-86 in a Model 16. Apparently, Veritas was having a hell of a time to get the board working properly with the new main board design of the Model 12. I imagine they gave up trying because there is no other history available on the board. Another short article in Basic Computing Vol 07 Num 01 1984 mentions that the DPO supported MS-DOS as well. Whether it actually did run MS-DOS, I'm not sure we will ever know.

  9. #9
    Join Date
    Jan 2013
    Marietta, GA


    It is also important to keep in mind that when discussing MS-DOS compatiblity that most MS-DOS applications require the IBM PC compatible hardware platform.

    It was possible to take a completely unique machine with nothing in common with the IBM PC other than an 8088/8086 CPU and port MS-DOS to it. These could run only simple "well behaved" programs that limited themselves to DOS I/O. There were a number of such machines early on.

    If that Dual Processor Option card ran MS-DOS it sounds like it would have been in that category.

    The 2000, on the other hand as I understand it, was "somewhat" IBM PC hardware compatible. I've never seen anyone detail precisely how compatible or incompatible it was. Off hand I know it used an 80186, which by itself is not 100% compatible, and 720K Quad Density disk drives, an issue for booters, and used its own port of DOS. But I've heard that it had CGA compatible-ish video, that would have let many IBM applications run.

  10. #10
    Join Date
    Jan 2011
    Portland, Oregon
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    The LNW Team ("TRS-80 Model 1, 3, and 4 Compatible") was advertised as having an "Optional 8088 CPU with MS-DOS":


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