Why was the Model I discontinued?

written by Matthew Reed

The TRS-80 Model I (originally known as the TRS-80 Microcomputer System) was introduced by Radio Shack on August 3, 1977. It was one of the first mass-marketed, fully-assembled microcomputers and quickly became the best-selling personal computer.

Yet despite continued demand, Radio Shack discontinued the Model I on January 1, 1981, slightly less than three and a half years after it was first introduced. The culprit was not customer demand (which remained high) but new radio interference regulations from the United States Federal Communications Commission (FCC) which took effect on that date.

FCC Part 15 Subpart J

The move to regulate radio interference from electronic devices predated personal computers, going back at least to 1976. (Some of the worst violators were cash registers which interfered with police and aviation communications.) The problem was that any metal surface in a device could act as an “unintentional radiator” and transmit interference being generated within.

The actual FCC rule in question was Part 15 Subpart J. It provided standards for acceptable levels of radio interference for electronic devices. All devices offered for sale had to meet the new rules or they could no longer be sold in the United States.

But the new rules were especially harsh on computers, creating two category of computing devices:

  • Class A: “marketed for use in a commercial, industrial or business environment(s)”
  • Class B: “marketed for use in a residential environment notwithstanding use in commercial, business and industrial environment(s)”

All microcomputer manufacturers faced the difficult prospect of modifying their existing computers to comply with the new rules. Most personal computers fell into the Class B category, including the TRS-80 Model I, the Apple II, and the Atari 400. The Class B rules took effect on January 1, 1981 and were much stricter than Class A. (Class A rules applied only to business computers such as the TRS-80 Model II and took effect later.)

The problem with the Model I

From its introduction, the Model I was well known for creating AM radio and television interference. This had a lot to do with its modular design. A typical Model I system consisted of multiple pieces, each connected by cables:

  • the main keyboard unit
  • a monitor
  • a cassette recorder
  • an Expansion Interface
  • one or more disk drives

Each of those parts could (and usually did) act as an antenna and radiate interference, as could any of the cables connecting them. The modular design made the Model I particularly vulnerable to the new FCC rules and made a simple redesign nearly impossible.


Rumors predicting the upcoming discontinuation of the Model I were widespread in mid-1980, especially after Radio Shack introduced two new computers, the Color Computer and the Model III. The Model III was mostly Model I compatible and featured an all-in-one design, which made stopping interference less of a problem.

Radio Shack finally confirmed in November 1980 that the Model I was being discontinued. Radio Shack President Lewis Kornfeld said in an interview that “warehouse and marketing space for the Model I will be taken up by the Model III and the Color Computer.” He further stated “Stopping production is not a surprise and not an insult. We haven’t issued a statement on this whole thing because we haven’t stopped anything at this point.”

Recalled or not?

It is often stated that Radio Shack was forced by the FCC to recall the Model I. That is incorrect and based on a misunderstanding of the FCC rules. The new FCC regulations applied only to hardware manufactured after January 1, 1981. Any non-certified product manufactured before that date could still be sold until July 1, 1982 as long as it displayed this label:

This equipment has not been tested to show compliance with new FCC rules (47 CFR Part 15) designed to limit interference to radio and TV reception. Operation of this equipment in a residential area is likely to cause unacceptable interference to radio communication requiring the operator to take whatever steps are necessary to correct the interference.

Radio Shack stopped production of the Model I in either November or December of 1980, so they were allowed to sell off their entire stock. Demand was so high that the Model I was sold out at stores before January 1981 was over.


Jon Shirley, Vice President of the Radio Shack Computer Division, wrote in the January 1981 issue of the TRS-80 Microcomputer News:

So, where does this leave you Model I owners? Still fully supported as all we have dropped is the Model I CPU. We are still making expansion interfaces, all upgrade kits, disk drives, etc. and we will continue to make them as long as there is a demand.

That turned out to be only partly true: the FCC decided that “computing devices” also applied to peripherals such as the Expansion Interface. Radio Shack never received FCC certification but did obtain an exemption to allow them to manufacture 30,000 Expansion Interfaces in 1981. After those were sold, the product was discontinued despite continuing demand.

Categories: FAQ


Terry Stewart says:

Hi Matthew,

It wasn’t just the Model 1. I remember by System 80 (so presumably the PMC-80 and Video Genie) used to broadcast well..and that was a single unit console!

Interestingly a few of the early game instructions urged people to take advantage of the Model 1’s broadcasting prowess. I remember one which instructed users to place an AM radio tuned to a blank space on the band in order to hear “sound effects” (lol). I can’t remember exactly what game it was but it may have been Swamp Wars.

Mark McDougall says:

There was definitely more than one game that used an AM radio for sound effects!!! I can’t recall at this time which games they were, but I recall playing several that used this method!

Phil says:

The Video Genie clone that I was running in the UK frightened the life out of me one day, for this very reason. Late at night, during an adolescent version of a hacking session and still at school, the computer suddenly spoke a complete sentence of what I have always guessed to be a police radio travelling past the house….not a regular happening. :)

Robert B says:

When I was doing assembly language programming on the Model I, it wasn’t unusual for me to cause the computer to enter an endless loop and freeze. An AM radio was an essential debugging tool… it would tell me if I was in a controlled loop waiting for input (like from my 300 baud modem), or if it was in a tight loop requiring a hard reset.

Jerry K says:

This brings back memories. Back around 1978, I ate beans for a month and bought a Model 1. It was the $600 version with Level 1 Basic. I quickly saved up an additional $200 and bought the Level II rom upgrade.

I learned to program on that beast, and went on to have a 20 year career in software engineering.

I remember how noisy it was. When I was computing, my wife would see

bars on her TV set across the house. I tried once to use it with my ham radio – with that computer computing, the ham bands would just disappear.