Looking at the TRS-80 Disk Software Page, there's a rather extensive selection of DOS options that seem to work with the 4P and also claim high compatibility with the Tandy "TRSDOS" option.

Considering that I have a 4P with two floppy drives, and I'd like to run Model III and Model 4 native software (not CP/M), is there a particular DOS which is considered superior? I think my main criteria are compatibility, ease-of-use, and easy booting into both Model 4 and Model III modes. The 4P has no Model III ROM, so the DOS needs to support disk loading it for compatibility with Model III programs.

Note: I'm not concerned about Y2K compatibility.

  • 1
    While not that much of a TRS buff, I've been told by people who know thet NewDOS is somewhat like the most common replacements, and MultiDOS eventually the best. AFAIK it was also available for next to any Z80 besed and TRS compatible computer, including model I/III/4, EACA VideoGenie and Lobo. on some machines even enabled to read disk of all others. Both seam to offer Model II ROM compatibility images. I would give MultiDOS a try with NewDOS being next in line.
    – Raffzahn
    Aug 11, 2018 at 21:02
  • A couple data points: My friend and I both ran TRSDOS and NewDOS on our TRS-80 Model I machines. Aug 14, 2018 at 19:44

1 Answer 1


Most TRS80 folks today run LSDOS 6.3.x as the main OS on the Model 4. The source is published, it's hackable and it is well supported by modern hardware like the M3SE and the FreHD. TRSDOS 6 was basically the same thing rebadged.

For Model III mode you need to get a copy MODELA/III and add it to a TRSDOS 1.3 or LDOS 5 diskette. It's documented in the Disk System Manual for the 4P.

If you need more help I would try somewhere like the Vintage Computer Forum (VCFED) forums as there are a fair number of Trash80 folks active on it.


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