Orchestra-90, also known as Orch-90, was a popular hardware sound add-on for the TRS‑80 Model III and Model 4, and later the Color Computer. It was created and sold by Software Affair of Sunnyvale (originally Santa Clara), California, along with Orchestra-85, the equivalent add-on for the TRS‑80 Model I. It became more popular when Radio Shack began selling a licensed version of Orchestra-90 in 1984. At its peak of popularity, there were over a thousand song files available from CompuServe, Delphi, and BBS’s around the world.

Both Orchestra-90 and Orchestra-85 were enhanced versions of Software Affair’s earlier Orchestra-80. Orchestra-85 (the Model I version) was introduced in 1981 for $129.95. Orchestra-90 (the Model III version) followed a few months later for $149.95. Users who wanted to upgrade the Orchestra-80 could send their unit to Software Affair and pay $69.95 (plus $2.00 for shipping and handling) to exchange it for an Orchestra-85.


Probably the biggest design mistake Radio Shack made with the TRS‑80 Model I was their decision to use solder-coated tin contacts (instead of silver or gold) on the Model I and Expansion Interface connectors. These solder-coated contacts tended to oxidize over time, leading to reliability problems and unexpected reboots. The usual solution was periodically to use a pink rubber eraser to remove the oxidation. This was supposed to be done every month, but many people did it every week, or even every day.

There were also several hardware solutions to the problem. The best known was the Gold Plug 80 from E.A.P. Company. Gold Plug 80 worked by installing gold-plated contacts over the originals. This completely eliminated the reliability problems. The only downside was that the double set of contacts did extend slightly from the case.

A lesser known way of stopping the reboots was Silver-It, sold by Roger Fuller through Fuller Software of Grand Prairie, Texas. Silver-It worked by recoating the oxidizing contacts with silver.

The TRS‑80 Model I

The Radio Shack TRS‑80 Microcomputing System (catalog number 26-1001), later known as the TRS‑80 Model I, was introduced by Radio Shack on August 3, 1977. It made computer history as one of the first mass marketed, fully assembled microcomputers. The initial price was $599.95, which included a typewriter-style (not membrane) keyboard, monitor, and cassette recorder.

The TRS‑80 (which became known as the Model I after the Model II was introduced in 1979) was created by Don French and Steve Leininger. It ran a Zilog Z80 at 1.77 MHz and came with 4K of RAM, and a 4K ROM of what was called Level I BASIC. Only uppercase characters could be displayed, and the only means of storage was a cassette recorder. Despite these limitations, the TRS‑80 was enormously successful. The initial production run sold out in less than a month, and it took almost a year for Radio Shack to catch up with the demand. Radio Shack sold 100,000 TRS‑80 computers in 1978, over four times its nearest competitor.

The Exatron MM+

The Exatron MM+, also known as the Exatron Memory Plus Expansion, was an alternative to the Radio Shack Expansion Interface for the TRS‑80 Model I. It was designed and sold by Exatron of Sunnyvale, California for use with their floppy disk storage alternative, the Exatron Stringy Floppy. Despite the fact that it was barely advertised and seems to have been only sold briefly in 1981, the Exatron MM+ remains one of the best remembered Expansion Interface alternatives.

The Exatron MM+ was aimed at users of alternative Model I storage options, such as the Exatron Stringy Floppy, the Meca BETA-80, or the JPC Products TC-8. Unlike the Radio Shack Expansion Interface, the Exatron MM+ didn’t include a floppy disk controller. But it did add additional memory, a parallel port, and a serial port. Unlike the Microtek MT-32, another lightweight Expansion Interface alternative, the Exatron MM+ also extended the Model I expansion bus. This meant that peripherals that connected to the bus, such as the Stringy Floppy or the BETA-80, could still be attached to the MM+.

TRSDOS Commented

There were many popular books published back in the late 1970’s and early 1980’s that examined the TRS‑80 Model I in detail. But there were far fewer books that served the same purpose for the TRS‑80 Model III.

TRSDOS Commented, published by Soft Sector Marketing with “decoding and data entry” by Rick Papo, was one of those few. The book’s cover described it as “a must for every Mod III owner.” It included a complete disassembly for the code comprising Model III TRSDOS (minus Disk BASIC) in much the same way as the IJG book TRSDOS 2.3 Decoded and Other Mysteries did for Model I TRSDOS. One notable difference was that the disassembled listings in TRSDOS 2.3 Decoded and Other Mysteries were published with full permission from Tandy Corporation. Soft Sector Marketing had no such permission and included this disclaimer at the beginning of TRSDOS Commented:

The Model I Printer Interface Cable

One of the limitations of the cassette-based TRS‑80 Model I was that it had no printer port. There were many cassette programs designed to use a printer, such as Electric Pencil and Scripsit, but no simple way to add one. Only a few Radio Shack printers were designed to connect to a cassette-based Model I directly.

The usual approach to adding a printer was to buy a Radio Shack Expansion Interface. In addition to providing extra memory and a floppy disk controller, the Expansion Interface also added a printer port. But a fully equipped Expansion Interface cost more than a Model I itself, and a unit with no memory still cost $299.00. Another option was a lighter-weight third-party Expansion Interface, such as the Microtek MT-32 or Exatron MM+. But this was still overkill if all you wanted was a printer.

The Custom TRS‑80 and Other Mysteries

The Custom TRS‑80 and Other Mysteries is one of the best remembered TRS‑80 books. It was written by Dennis Báthory-Kitsz and published by IJG, Inc (also known as the International Jewelry Guild). The first printing sold out in less than a month and the book ended up selling 50,000 copies around the world in three printings. The Custom TRS‑80 and Other Mysteries (which was volume 3 in IJG’s TRS‑80 Information Series) offers an interesting and entertaining look at the hardware and software inside the TRS‑80 Model I, the custom TRS‑80 of the title.

Dennis Báthory-Kitsz was well known for his TRS‑80 writing, including his articles in The Alternate Source and his “80 Applications” column in 80 Microcomputing. (Some of the information in The Custom TRS‑80 and Other Mysteries had previously appeared in his Alternate Source articles.)

The Kill Command

The KILL command was probably the most unusually named command in the TRSDOS disk operating systems for TRS‑80 computers. KILL was used to delete a file, for example: KILL FILENAME/EXT.

The KILL command was supported by versions of TRSDOS for the Model I, Model III, and Model II, as well as the BASIC interpreters for all those machines plus the Model 4, Color Computer, the Model 100, Model 102, Model 200, and the Model 2000. In addition, all of the TRSDOS-compatible TRS‑80 Model I/III operating systems (NEWDOS, MULTIDOS, DOSPLUS, and LDOS) also implemented the KILL command.

The use of KILL as a command was somewhat controversial and many people objected to the connotation. Here’s what Josef Friedman said about KILL in his article “Thou Shalt Not Kill” in the November 1984 issue of 80 Micro:

The Microtek MT-32

By itself, the TRS‑80 Model I was capable of only limited expansion. In order to add memory beyond 16K and support floppy disk drives, Radio Shack sold an external device they called an Expansion Interface.

The Expansion Interface could expand memory to 48K, add a parallel printer port, and add a disk controller for connecting floppy disk drives. But an Expansion Interface with 32K of memory cost $597.00, almost $100 more than a 4K Model I. What if a Model I owner didn’t want (or couldn’t afford) disk drives but still wanted to add memory and a printer port?

The MT-32 from Microtek, Inc. of San Diego, California used a different approach from the Radio Shack Expansion Interface. The MT-32, introduced in mid-1980, offered only two features: the ability to add 32K of RAM (for a total of 48K) and a parallel printer port.

MOD III ROM Commented

There were many books written that described and in some cases disassembled the TRS‑80 Model I BASIC ROM. A few of the more famous examples were Microsoft BASIC Decoded and Other Mysteries from IJG, Inc., The B00K from Insiders Software Consultants, Pathways Through the ROM from SoftSide Publications, and Level II ROMs from Tab Books. But there were far fewer books serving the same purpose for the TRS‑80 Model III BASIC ROM.

One of the best sources of information about the Model III ROM was TRS‑80 ROM Routines Documented by Jack Decker, which was published in 1983. But probably the best known was MOD III ROM Commented from Soft Sector Marketing. MOD III ROM Commented was published in 1981 with two printings. It contains a very detailed disassembly of the Model III BASIC ROM. As the book cover promised: “Not a rehash of old information, but an explanation of ROMS in the latest machine from Tandy.”