TRS‑80 Assembly Language Programming

At one time in the TRS‑80 world, the name William Barden was linked to assembly language programming. This book was one of the main reasons why. TRS‑80 Assembly Language Programming, along with Programming the Z80 by Rodney Zaks, helped introduce a whole generation of TRS‑80 programmers to assembly language.

The Alternate Source

The Alternate Source, also known as The Alternate Source Programmer’s Journal or TAS, was a well-remembered and very technical TRS‑80 publication. Later billed as “The magazine of advanced applications and software for the TRS‑80,” the first issue was published by Joni Kosloski and Charley Butler in January 1980. It was published once every two months for a total of six issues a year.

The concept behind The Alternate Source originated in October 1979. The Alternate Source was also the name of a company run by Butler and Kosloski that sold TRS‑80 books and software. TASMON (The Alternate Source Monitor) was one of their more popular software packages. They also sold The Alternate Source in book form, with each year’s issues collected into one volume.

Computer User

Computer User was a short-lived TRS‑80 magazine created by the publishers of Interface Age, a popular computer magazine that began in 1976.

Unlike many other TRS‑80 magazines, Computer User was a professional, glossy publication from its first issue in November 1983. It was heavily promoted, with promotional copies of the premiere issue sent to subscribers of competing magazines.

The Percom Doubler

The Percom Doubler was the first successful double-density add-on for the TRS‑80 Model I. It was introduced in 1980 by Percom Data Company for an initial price of $219.95. The Doubler hardware was designed by Wayne Smith and Harold Mauch (president of Percom) and the accompanying software was written by Jim Stutsman.


VTOS (which stood for “Virtual Technology’s Operating System”) was the second TRS‑80 Model I operating system created by Randy Cook, the author of Model I TRSDOS. VTOS was released in 1979 and sold through Randy Cook’s company, Virtual Technology Inc. The original price was $49.95 for VTOS version 3.0. That was increased to $99.95 for version 4.0, or $125.00 for VTOS plus Operator’s Guide and Master Reference manual. There doesn’t appear to have been a Model III version of VTOS.

The Patch

The Patch was a unique all-hardware approach to implementing lower case on a TRS‑80 Model I. It was sold by CECDAT Inc. for a price starting at $69.97.

The normal approach to adding lower case involved a hardware modification plus a software driver. Radio Shack never added a lower case driver to the Model I ROM, so the separate driver was required to enable generation of lower case characters. The lower case driver was stored in RAM, so it needed to be loaded again from cassette or disk every time the Model I was used.

The Patch combined an ordinary lower case hardware modification with a “patch” to the Model I ROM that added a lower case driver. Probably the best description of how it worked comes from one of their advertisements:

Irvin Mike Schmidt (1932–2009)

I was saddened to learn that Irvin Mike Schmidt passed away on February 16, 2009. Usually credited as I. Schmidt or Mike Schmidt, he was the founder and driving force behind 80-U.S. Journal, the TRS‑80 magazine that he published from 1978 to 1984. He was the editor-in-chief for most of its run and his influence was very evident in the magazine.

You can read an obituary for him here.

80-U.S. Journal

80-U.S. Journal was the best remembered name for a TRS‑80 magazine that was published by 80-Northwest Publishing from 1978 to 1984. It was also published under the names 80-Northwest Journal and Basic Computing. Until 1982, it was published bimonthly (six issues a year) but it increased to monthly (twelve issues a year) after that.

80-Northwest Journal (sometimes called 80-NW Journal) was first published in 1978 with the September/October issue. The founder of the magazine, Irvin “Mike” Schmidt, described the reason behind the new publication in the first issue:

The TRX-280

The TRX-280 was a proposed motherboard replacement for the TRS‑80 Model 4, described in the December 1990 issue of Computer News 80 and issue 38 of TRSLINK. It was created by Peter Ray of Anitek Software Products in an attempt to design a “next generation” TRS‑80.

The TRX-280 design was based around the Z280, an enhanced Z80 compatible processor created by Zilog. The Z280 was an interesting chip, providing software compatibility with the Z80 yet adding many new features, such as a memory management unit, new addressing modes, and new instructions. It was also faster than the Z80 at the same clock speed.

The TRX-280 was planned as a drop-in replacement for the Model 4 motherboard (and possibly the Model III as well). It would have remained compatible with all TRS‑80 software and hardware, with the one exception that it would have lacked a cassette port.

The TRX-280 had an impressive set of proposed features:

The LNW System Expansion

The LNW System Expansion was a popular alternative to the Radio Shack Expansion Interface. Introduced in 1979 by LNW Research, the System Expansion was the most popular of the Expansion Interface replacements. LNW Research later described themselves as “the number one manufacturer of system expansion units and accessories for the Model I computer”.

The LNW System Expansion sold for $69.95 as a kit with a bare printed circuit board and manual. LNW later introduced the $399.95 LNW System Expansion II, which provided the same features but came assembled in a metal case.