High-resolution graphics for the TRS‑80

Unlike many competing computers, the TRS‑80 Model I lacked any form of built-in high-resolution graphics. Although some TRS‑80 compatible computers, such as the LNW80, offered high-resolution as a feature, the only graphics possible with the Model I were relatively low-resolution 128 by 48 block graphics. The many games written for the Model I made good use of these block graphics, and Radio Shack never made high-resolution a standard feature of the Model I, III, or 4. Several companies created products to address this deficiency, with some becoming more popular than others.

The SubLOGIC 50/T80

The SubLOGIC 50/T80 was a high-resolution add-on for the TRS‑80 Model I. It was created by SubLOGIC, a company better known to TRS‑80 users for their T80-FS1 Flight Simulator.

Here is the text of the 1980 product introduction:

The SubLOGIC 50/T80 system is a high performance professional graphics display system designed to be used directly with the TRS‑80. It provides the high-resolution graphics capability which the 80 lacks—the kind of graphics needed for scientific, engineering, and educational applications. Dense drawings, graphs, and even alphanumerics can be put on the 50/T80’s 256 by 240 dot screen. The 50/T80 has the support of SubLOGIC’s 2D and 3D graphics packages, which are powerful and easy to use. They operate easily from BASIC as well as assembly language.

The Model 4 Grafyx Solution

The Model 4 Grafyx Solution was the most popular high-resolution add-on for the TRS‑80 Model 4, and probably the most popular Model 4 add-on in general. It was introduced in 1984 for a price of $199.95 by Micro-Labs, creators of the earlier Model III Grafyx Solution. The Model 4 Grafyx Solution provided true high-resolution access to every pixel on the 640 by 240 Model 4 display, yet was easily user-installable in only a few minutes.

Unlike the Model III Grafyx Solution, which was memory mapped, the Model 4 Grafyx Solution was port-mapped. It used the same ports and mapping as the Radio Shack Model 4 high-resolution board. This meant that the Model 4 Grafyx Solution was almost completely compatible with the Radio Shack board and they could run the same programs. This had the odd side effect of making the Model 4 Grafyx Solution in Model III mode incompatible with the Model III Grafyx Solution.

The Model 4 Grafyx Solution had many advantages compared to the Radio Shack board:


Level III BASIC was an enhanced version of Level II BASIC for the TRS‑80 Model I. It was created by Microsoft, also the authors of Level II BASIC, but sold by GRT Corporation on cassette for $49.95. Level III BASIC was said to be the first consumer product from Microsoft, which had previously sold only to manufacturers.

Rather than sell Level III BASIC directly to consumers, Microsoft decided to release it through GRT Corporation in 1978. GRT Corporation, which stood for Great Records and Tapes, was a music company that had expanded into the software business. The GRT software division, named G2, was started by Vern Raburn and Level III BASIC was sold under the G2 label.

The Level III BASIC manual contains this surprising statement of authorship:


The TRS‑80 VOXBOX (catalog number 26-1181) was an early microcomputer speech-recognition product for the TRS‑80 Model I. Introduced in July 1979 by Radio Shack for a price of $169.95, the VOXBOX was described as “electronic ears for your Model I.” The VOXBOX was only available for the Model I; there never was a version for the Model III.

Here is a description of the VOXBOX from a 1980 Radio Shack catalog, where it was paired with the $399 TRS‑80 Voice Synthesizer:

The TRS‑80 “Model 5”

Radio Shack introduced the TRS‑80 Microcomputer System, later known as the Model I, in August 1977. It was the first member of the original line of TRS‑80 computers. Radio Shack followed the Model I with the mostly compatible Model III in 1980 and then the Model 4 in April 1983. But other than the transportable Model 4P in November 1983 and the improved Model 4D in 1985, there were no further members of this computer family.

Around the time of the development of the Model 4, Radio Shack engineers did plan a computer that could have followed it. Although not known by the name within Radio Shack, this often rumored computer was usually called the “Model 5” or the “Model 4C” by the public.

By considering all of the available bits of information, it is possible to piece together details about the key features of the “Model 5”:

The Radio Shack Model 4 High-Resolution Board

Radio Shack introduced their high-resolution add-on for the Model 4 (catalog number 26-1126) on October 15, 1983. Just like their Model III high-resolution board, it was never identified by name in any Radio Shack catalog. The official name seems to have been “TRS‑80 Model 4 Computer Graphics” but it was usually referred to as the “Radio Shack Model 4 high-resolution board.”

At $249.95, the Model 4 high-resolution board was $80 cheaper than the Model III version. It provided a nearly identical hardware interface to the Model III version, with the same 640 by 240 resolution. It’s interesting to note that the Macintosh screen at the time was 576 by 340.


PC-Four was the first TRS‑80 Model 4 emulator for IBM PC compatible computers. It was written by Michael Gingell and introduced by Hypersoft in mid-1987 for a price of $79.95. PC-Four required a computer with at least 384K of memory and worked on both floppy and hard drive systems.

PC-Four (sometimes referred to as PC4) was quite different than later TRS‑80 emulators. It achieved most of its compatibility not through Model 4 hardware emulation but by emulating the Model 4 operating system. This approach (similar to the MS-DOS emulator DOSBox today) allowed PC-Four to approximate Model 4 speed when running on a Tandy 1000 SX. The PC-Four manual described it this way:

The LNW Team

The LNW Team was an intriguing idea for a computer to bridge the TRS‑80 and MS-DOS worlds. It was sold by LNW Computers, the company responsible for the LNW System Expansion, the LNW80, and the LNW80 Model 2.

The computer appears to have been the same externally as the LNW80 Model 2, although the standard memory was increased to 160K and the clock speed increased to 5.3 MHz. What really set the LNW Team apart was the optional 8088 board.

Why was the Model I uppercase only?

One of the biggest weaknesses of the TRS‑80 Model I was the lack of lowercase characters on the screen. Although that omission was hardly unique to the Model I (many computers at the time lacked lowercase, including the Apple II), it was still a notable limitation that affected many applications, especially word processing.

The two people most responsible for the Model I (originally known as the Radio Shack TRS‑80 Microcomputer System) were Don French and Steve Leininger. Don French, described as “the originator of the TRS‑80 project,” was a buyer for Radio Shack who had long pushed for Radio Shack to manufacture a microcomputer. Steve Leininger was the engineer who designed almost all of the hardware of the Model I and created the original Level I BASIC.

Steve Leininger mentioned lowercase in a talk he gave to the San Diego Computer Society in September 1977, just one month after the TRS‑80 was introduced: