Definitive List of TRS-80 Model II Operating Systems

Model II Operating Systems (in chronological order)


TRSDOS Model II Version 1.1/1.2 The original Model II Z80 operating system which was released with the first Model II in 1978. Supports SSDD 8” floppy drives only. Was replaced by 2.0 fairly quickly.

TRSDOS Model II 1.2

TRSDOS 2.0 The second OS release for the Model II probably circa 1979. Many bug fixes and enhancements over TRSDOS 1.1/1.2 but they are completely incompatible formats. Referred to as 2.0a once 2.0b became available.


TRS-80 Model II Disk Operating System Reference Manual

TRSDOS 2.0b Released with the Model 16 in 1982 with support for the Thinline Tandon 848 drives. Otherwise the same as 2.0a.


TRSDOS 2.0d This was an officially unreleased TRSDOS 2.0 version that supported both the SSDD Model II and the DSDD Thinline Model 12/16 drives.

TRSDOS HD There are references to TRSDOS-HD in the Model 16 documentation set but I have never seen it and not sure if it ever was released. This is in all likelihood an early name for what turned out to be TRSDOS-II 4.0.

TRSDOS-II 4.0 Completely new third Model II OS with HD support. This release actually requires a hard drive adapter because the OS requires 64k + 16K (found on the HDA). The hard drive needed to be initialized with the Hard Disk Initialization System which ran under TRSDOS 2.0.

TRSDOS-II Reference Manual

TRSDOS-II 4.1 Introduced with the Model 16. Added support to bootstrap the new TRSDOS-16. OS could now use 16k from the 68000 memory on a Model 16 so it did not require a HDA on these machines.


TRSDOS-16 First 16 bit operating system released for the Model 16. Uses TRSDOS II 4.1 as a boot loader. Makes extensive use of TRSDOS || 4.1 under the covers. The most hybrid and hence most complicated and hence most problematic Tandy OS released.

TRSDOS-16 Disk Operating System

TRSDOS-II 4.2 Introduced with the Model 12. The OS could now also use the additional 16K from the B design machine’s motherboard so it did not require a HDA on these machines. This was the first release with complete HD support and did not require the external TRSDOS 2.0 based hard drive initialization utility. There were many iterations of 4.2.x which supported different combinations of HD adapters and controllers.


TRSDOS-II 4.3 Added Arcnet support.

TRSDOS-II 4.4 Unreleased final version of TRSDOS-II

TRS-XENIX 1.x Released for the Model 16 after Tandy realized TRSDOS-16 was a flop. Licensed from Microsoft.

TRS-Xenix Operations Guide

TRS-XENIX 3.x Released for the Model 6000. Requires the 8Mhz 68000 CPU board found in the 6000. The 6Mhz board in the 16B can be upgraded to 8Mhz according to Tech Bulletin 12/16B:044.

TRS-XENIX 3.2 Install


P&T CP/M 2.2 Pickels and Trout CP/M is considered by many to be the de-facto Model II CP/M implementation.

Pickels and Trout CP/M 2.2mH

Lifeboat CP/M

Lifeboat CP/M on TRS-80

Aton CP/M

Version 2.23I

CP/M-68K A 68000 version of CP/M that runs on the 68K subsystem in the TRS-80 that requires any one of the z80 CP/M 2 operating systems to be installed. It is similar to TRSDOS-16 in that it uses the underlying 8-bit operating system as a boot loader and I/O system. A very interesting feature is that you can switch between z80 CPM and 68k CPM and back without losing the 68k context.

TriSoft CP/M-68K TRS-80 User’s Guide

CP/M Plus Tandy badged version of CP/M 3 from DRI. It supported bank switching on the Model 12/16B/6000 so could utilize 128K of z80 memory if the machine was upgraded appropriately. See Tech Bulletin 12/16B:18.

Non-Tandy Other

LS-DOS 6.3.1A Compatible with the Model 4 version of LS-DOS 6.3.1. Can also utilize the optional additional z80 64K on the main logic board on the 12/16B/6000. See details below. Can be downloaded here.


DOSPLUS II A00, A01 & A01D

3 thoughts on “Definitive List of TRS-80 Model II Operating Systems

  1. David Sutherland

    Regarding DOSPLUS for the Model II, in 2005 I contacted Steve Pagliarulo asking if he had the source code still and unfortunately he said he had looked but could not find it.
    Steve Pagliarulo

    Hi David,

    It’s fun to go back and remember what was. Thanks. I’ve checked my attic/garage, etc. and can’t find anything I can donate or lend. I’m sorry. If however I open an unopened storage box in the future and discover something, I’ll let you know. Feel free to contact me any time.

    Best Wishes,

    From: David Sutherland
    Reply-To: David Sutherland
    To: Steve Pagliarulo

    Subject: Re: TRS-80 / DOSPLUS-II Disks?
    Date: Sun, 22 May 2005 17:31:17 -0500

    I apologize for being so brief in my email–I wasn’t sure I had a valid
    email address so intentionally left out a lot of information.

    I think I tracked you down last night via a google usenet search. It seems
    useful these days to have a name other than “Steve Smith”–fortunately for
    me, your name is unique!

    I was prompted to write after reading a recent 80-US Journal article
    interview with you and Kim Watt. This issue has recently been scanned and
    posted at the TRS-80 information archive, if
    you are interested in re-reading some TRS-80 lore.

    I believe Kim had loaned out his TRS-80 diskette archive to Tim Mann and to
    Ira @ the site. At one time on the
    trs-80.comsite there were some partial source code
    listings of DOSPLUS II. …

    Is there any chance you still have Model 1/3 or Model 2 source code that
    you’d be willing to allow to be publicly archived?

    Hope if nothing else these were memories of good times for you.

    Thanks for considering this. Hope you might have kept a few boxes of disks
    in your attic.

  2. David Sutherland

    Also, Aaron Brockbank got in touch with Steve Pagliarulo and was attempting to recreate DOSPLUS from source code:

    I trust sharing this is not a breach of any privacy:

    Dec 17, 2007


    Thank you for the source. After examining it, I realize that I barely even remember writing it… However, the source was compiled with the MZAL assembler on a Model 4 as I recall. Reasons the binaries are hard to re-create:

    1) Access to Model 4 (or simulator)
    2) Access to MZAL assembler for Model 4. I don’t believe the Model III MZAL had enough memory.
    3) Not sure ALL the source code still exists
    4) A special tool was used to create the disk images (no longer exists)

    Regarding the patch, I remember there being an upgrade but the details escape me. Sorry.


  3. David Sutherland

    Aaron mentioned DOSPLUS-II versions and patches also, which might be helpful to anyone looking for more information on this OS. That is the question above which Steve was responding to.

    > There is a letter attached to the copy of the DOSPLUS-II manual that I
    > got from ebay (sadly, no disk). It mentions DP-II A.01, an upgrade to
    > DOSPLUS-II. Also mentioned is a separate patch to allow dates past
    > 1987. Do you recollect anything about these?


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