TRSDOS for the Model I

TRSDOS in Radio Shack catalog

TRSDOS from a Radio Shack catalog

TRSDOS, referred to as DOS in some early references, was Radio Shack’s official disk operating system for the Model I. The name stood for Tandy Radio Shack Disk Operating System. It was bundled with Radio Shack’s floppy disk upgrade, but it could also be purchased separately.

TRSDOS consisted of a command shell and a Disk BASIC with extended features. Unlike many other computers at the time, the Model I was designed to support floppy drives as a future option. The Level II ROM booted from a floppy disk if available, and the ROM BASIC included special hooks to support Disk BASIC commands.

The design and code of TRSDOS (with the exception of Disk BASIC) was the product of Randy Cook. Shugart, the company which was manufacturing floppy drives for Radio Shack, recommended Cook as an expert in floppy disk interfacing. According to a 1981 interview with Randy Cook, Radio Shack paid him a flat fee of $3000 for developing TRSDOS.

TRSDOS has been heavily criticized over the years, but there are several important points to remember:

  • TRSDOS 2.0 contained many bugs, but Randy Cook never intended it to be released to the public. Most of the major bugs were fixed in TRSDOS 2.1.
  • TRSDOS provided a far more robust and powerful framework than most other microcomputer operating systems at the time. It featured passwords, overlays, fast directory access through hashing, command line parameters, and both byte and sector I/O. Other features, such as interrupt tasks, device drivers, redirection, and filtering, were present in the original version but only documented later.
  • Many of the reliability problems blamed on TRSDOS were actually the fault of hardware, such as flaky floppy drives or the cable connection with the Expansion Interface.

After the release of TRSDOS 2.1, Randy Cook parted company with Radio Shack and created another operating system, VTOS, which he sold through his own company. This means that Randy Cook had an important influence on all of the major TRS‑80 operating systems:

  • DBLDOS was a patched version of TRSDOS.
  • NEWDOS and DOSPLUS originally were patched versions of TRSDOS. Later versions were completely rewritten.
  • ULTRADOS was originally a patched version of TRSDOS.
  • MULTIDOS was a completely rewritten version of ULTRADOS.
  • VTOS was Randy Cook’s own continuation of TRSDOS.
  • LDOS was created by Logical Systems from the VTOS source code under an agreement with Randy Cook.

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