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This article is about the original TRS-80 (Model I) and its successors (Models III and 4). For an overview of all computers using the TRS-80 and Tandy names, see List of TRS-80 and Tandy-branded computers. For other uses, see TRS-80 (disambiguation).
TRS-80 Model I
TRS-80 Model I with Expansion Interface
Manufacturer Tandy Corporation
Type Home computer
Release date August 3, 1977; 42 years ago (1977-08-03)[1]
Discontinued January 1981; 39 years ago (1981-01)
Operating system TRS-DOS, NewDos/80
CPU Zilog Z80 @ 1.774 MHz
Memory 4 KB ~ 48 KB

The TRS-80 Micro Computer System (TRS-80; later known as the Model I to distinguish it from successors) is a desktop microcomputer launched in 1977 and sold by Tandy Corporation through their Radio Shack stores. The name is an abbreviation of Tandy/Radio Shack, Z-80 microprocessor.[2] It was one of the earliest mass-produced personal computers.[3]

By 1979, the TRS-80 had the largest selection of software in the microcomputer market.[4] Until 1982, the TRS-80 was the best-selling PC line, outselling the Apple II series by a factor of 5 according to one analysis.[5]

In mid-1980, the broadly compatible TRS-80 Model III was released. The Model I was discontinued shortly after, primarily due to stricter FCC regulations on the massive radio-frequency interference it caused in surrounding electronics.[6][7] In 1983, the Model III was in turn succeeded by the compatible Model 4.

As well as the original Model I and its compatible descendants, the TRS-80 name was later used as a generic brand on other technically unrelated computer lines sold by Tandy, such as the TRS-80 Model II, TRS-80 Color Computer and TRS-80 Pocket Computer.


File:Radio Shack Tandy TRS-80 Model I System.JPG
Radio Shack Tandy TRS-80 Model I System

In the mid-1970s, Tandy Corporation's Radio Shack division was a successful American chain of more than 3,000 electronics stores. After buyer Don French purchased a MITS Altair kit computer, he began designing his own and showed it to vice president of manufacturing John Roach. Although the design did not impress Roach, the idea of selling a microcomputer did. When the two men visited National Semiconductor in California in mid-1976, Steve Leininger's expertise on the SC/MP microprocessor impressed them. National executives refused to provide Leininger's contact information when French and Roach wanted to hire him as a consultant, but they found Leininger working part-time at Byte Shop and he and French began working together in June 1976. The company envisioned a kit, but Leininger persuaded the others that because "too many people can't solder", a preassembled computer would be better.[8][9][10]

Tandy had 11 million customers that might buy a microcomputer, but it would be much more expensive than the US$30 median price of a Radio Shack product, and a great risk for the very conservative company.[10] Many opposed the project; one executive told French, "Don't waste my time—we can't sell computers." As the popularity of CB radio—at one point more than 20% of Radio Shack's sales—declined, however, the company sought new products. In December 1976 French and Leininger received official approval for the project but were told to emphasize cost; for example, leaving out lowercase characters saved US$1.50 in components and reduced the retail price by US$5. In February 1977 they showed their prototype, running a simple tax-accounting program, to Charles Tandy, head of Tandy Corporation. The program quickly crashed as the computer could not handle the US$150,000 figure that Tandy typed in as his salary, and the two men added support for floating-point math to its Tiny BASIC to prevent a recurrence. After the demonstration Tandy revealed that he had already leaked the computer's existence to the press, so the project was approved.[10][11]

MITS sold 1,000 Altairs in February 1975, and was selling 10,000 a year. Leininger and French suggested that Radio Shack could sell 50,000 computers,[12] but others disagreed and suggested 1,000 to 3,000 per year at the target US$199 price. Roach persuaded Tandy to agree to build 3,500—the number of Radio Shack stores—so that each store could use a computer for inventory purposes if they did not sell.[4][8][9][11][13]

Having spent less than US$150,000 on development, Radio Shack announced the TRS-80 (Tandy Radio Shack) at a New York City press conference on August 3, 1977. It cost US$399, or US$599 with a 12" monitor and a Radio Shack tape recorder as datacassette storage; the most expensive product Radio Shack previously sold was a US$500 stereo. The company hoped that the new computer would help Radio Shack sell higher-priced products, and improve its "schlocky" image among customers. Small businesses were the primary target market, followed by educators, then consumers and hobbyists; despite its hobbyist customer base, Radio Shack saw them as "not the mainstream of the business".[9][14][12][15]

Although the press conference did not receive much media attention because of a terrorist bombing elsewhere in the city, the computer received much more publicity at the Personal Computer Faire in Boston two days later. A front-page Associated Press article discussed the novelty of a large consumer-electronics company selling a home computer that could "do a payroll for up to 15 people in a small business, teach children mathematics, store your favorite recipes or keep track of an investment portfolio. It can also play cards." Six sacks of mail arrived at Tandy headquarters asking about the computer, over 15,000 people called to purchase a TRS-80—paralyzing the company switchboard—and 250,000 joined the waiting list with a $100 deposit.[9][4][12][16][17]

Despite the internal skepticism, Radio Shack aggressively entered the market. Company president Lewis Kornfeld stated when announcing the TRS-80, "This device is inevitably in the future of everyone in the civilized world—in some way—now and so far as ahead as one can think", and Tandy's 1977 annual report called the computer "probably the most important product we've ever built in a company factory". Unlike competitor Commodore—which had announced the PET several months earlier but had not yet shipped any—Tandy had its own factories and distribution network, and even small towns had Radio Shack stores. The company announced plans to by Christmas sell a range of peripherals and software for the TRS-80, began shipping computers by September, and opened its first computer-only store in October. Still forecasting 3,000 sales a year, Radio Shack sold over 10,000 TRS-80s Model Is in its first one and a half months of sales, and over 200,000 during the product's lifetime;[17][8][18][9][11][4][15][13][19]:4[14] one entered the Smithsonian's National Museum of American History.[20]

The first units, ordered unseen, were delivered in November 1977, and rolled out to the stores the third week of December. The line won popularity with hobbyists, home users, and small-businesses. Tandy Corporation's leading position[citation needed] in what Byte Magazine called the "1977 Trinity" (Apple, Commodore and Tandy) had much to do with Tandy's retailing the computer through more than 3,000 of its Radio Shack storefronts.[21] Notable features of the original TRS-80 included its full-stroke QWERTY keyboard, small size, its floating-point BASIC programming language, an included monitor, and a starting price of US$600[1] (equivalent to US$2300 in 2019). The pre-release price was US$500 and a US$50 deposit was required, with a money-back guarantee at time of delivery.

By 1980 InfoWorld described Radio Shack as "the dominant supplier of small computers".[22] Kilobaud Microcomputing estimated that it was selling three times as many computers as Apple Computer, with both companies ahead of Commodore.[23] By 1981 hundreds of small companies produced TRS-80 software and accessories,[24] and Adam Osborne described Tandy as "the number-one microcomputer manufacturer" despite having "so few roots in microcomputing".[25] Roach became Tandy's CEO that year, Leininger became director of strategic planning, and French founded a software company. Although selling computers did not change the company's "schlocky" image, the Radio Shack name embarrassed business customers, and Tandy executives disliked the "Trash-80" nickname for its products, by 1984 computers accounted for 35% of sales and the company had 500 Tandy Radio Shack Computer Centers.[8][11][15][26]

Following the Model III launch in mid-1980, Tandy initially claimed that the Model I had not been dropped.[27] However, it had been discontinued by the end of the year. Tandy cited one of the main reasons as being the prohibitive cost of redesigning it to meet stricter FCC regulations covering the significant levels of radio-frequency interference emitted by the original design.[6][7] The Model I radiated so much interference that while playing games an AM radio placed next to the computer could be used to provide sounds.[28]


File:Radio Shack Tandy TRS-80 Model I PCB.JPG
Radio Shack Tandy TRS-80 Model I PCB
File:Radio Shack Tandy TRS-80 Model I Rear Panel.JPG
Radio Shack Tandy TRS-80 Model I Rear Panel Connectors
File:Radio Shack Tandy TRS-80 Model I Level II ROM Upgrade PCB.JPG
Radio Shack Tandy TRS-80 Model I Level II ROM Upgrade PCB

The Model I combined the mainboard and keyboard into one unit, in what was to be a common case design trend throughout the 8-bit microcomputer era, although it had a separate power supply unit. It used a Zilog Z80 processor clocked at 1.77 MHz (later models were shipped with a Z80A). The basic model originally shipped with 4 KB of RAM, and later 16 KB.[9]


File:Radio Shack Tandy TRS-80 Model I Keyboard.JPG
Radio Shack Tandy TRS-80 Model I ALPS Keyboard PCB

The implementation of the keyboard was unusual. Instead of transferring data through an I/O chip, the hardware mapped the keyboard to dedicated locations in the processor's memory. Performing a read from the keyboard area of the memory would return the state of a particular set of keys.

A version of the computer was produced which replaced the nameplate with a numeric keypad.

Many users complained about the TRS-80 keyboards, which used mechanical switches and suffered from "keyboard bounce", resulting in multiple letters being typed accidentally.[29] The problem was so widespread that Wayne Green's editorial in the first issue of 80 Micro mentioned it.[30] A Keyboard De-Bounce tape was distributed, which altered the system's software to reduce the effect of bounce and to slow down polling of the keyboard. Eventually, this change was added to a later ROM revision. The keyboard hardware was also changed to be less vulnerable to bounce.

Video and audio

The TRS-80 was accompanied by a modified RCA black-and-white television. The color of the screen text is light bluish (the standard "P4" phosphor used in black-and white televisions). Green and amber filters, or replacement tubes to make the display easier on the eyes, were common aftermarket items. Later models came with a green-on-black display.

Because of bandwidth problems in the interface card that replaced the TV's tuner, the display would lose horizontal sync if large areas of white were displayed; a simple hardware fix (involving less than half an hour's work) could be applied to correct that.

The video hardware can only display text at 64 or 32 characters wide by 16 lines of resolution.[9] This is because the video memory system uses a single kilobyte of video memory. Seven bits of each byte are used to display ASCII characters, with the eighth bit used to differentiate between text and "semigraphics" characters.

Primitive graphics ("text semigraphics", rather than a true bitmap) can be displayed because the upper 64 characters of the 128-character set appear as a grid of 2×3 blocks resembling Teletext. BASIC routines can write directly to the virtual 128×48 grid.

The original TRS-80 Model I could not differentiate between upper and lower characters in display memory. With only seven 1-bit-wide memory chips, the 8th bit was faked by circuitry that forced uppercase characters. The display hardware did have lowercase letters, but without descenders. In order to display lower case, owners had to add an eighth memory chip. This modification became a popular third-party add-on, along with a character chip with descenders for the lowercase letters. Later models came with the hardware for lowercase character set to be displayed with descenders.

Many users complained about the poor quality of the video display; as Green wrote, "hells bells, [the monitor] is a cheap black and white television set with a bit of conversion for computer use".[30] (The computer could be purchased without the Radio Shack monitor.)[17] Any access to the screen memory caused "flicker" on the screen. The bus arbitration logic would block video display while access was given to the CPU, causing a short black line. This had little effect on normal BASIC programs, but fast programs made in assembly language could be affected. Many software authors were able to minimize this effect. Notwithstanding this primitive display hardware, many arcade-style games were available for the Tandy TRS-80.

The Model I has no sound hardware. Square wave tones can be produced by outputting data to the cassette port and plugging headphones or an amplifier into the Data Out line. Some games use this ability for sound effects. An adapter was available to use Atari joysticks.[31]


Cassette tape drive

User data was originally stored on cassette tape. Radio Shack's model CTR-41 cassette recorder was included with the US$599 package.[19]:3–4 The software-based[8] cassette tape interface was very slow and erratic;[29] Green described it as "crummy ... drives users up the wall", and the first issue of 80 Micro had three articles on how to improve cassette performance.[30] It was sensitive to audio volume changes,[17] and the machine gave only the very crudest indication as to whether the correct volume was set, via a blinking character on screen when data was being loaded. To find the correct volume, one would sometimes have to attempt to load a program once, adjusting volume until the machine picked up the data, then reset the machine, rewind the tape and attempt the load again. Users quickly learned to save a file three or more times in hopes that one copy would prove to be readable. Automatic gain control or indicator circuits could be constructed to compensate for this (the owner's manual provided complete circuit diagrams for the whole machine, including the peripheral interfaces, with notes on operation).

An alternative tape interface could receive transmissions from the BBC's Chip Shop programme in the UK, which broadcast software for several different microcomputers over the radio. A special program (loaded using the conventional tape interface) was needed to access the custom interface. Tandy eventually replaced the CTR-41 unit with the CTR-80 which had built-in AGC circuitry (and no volume control). This helped the situation, but tape operation was still unreliable.

TRS-80s with Level I BASIC read and wrote tapes at 250 bits per second (31.25 bytes per second); Level II BASIC doubled this to 500 bits per second (62.5 bytes per second). Some programmers wrote machine language programs that would increase the speed to up to 1800 bits per second without loss in reliability.

For loading and storing data, no hardware controller existed. Instead, the processor created the sound itself by switching the output voltage between three states, creating very crude sine wave audio.

The first models of the Model I also had problems reading from the cassette drives. Tandy eventually offered a small board which was installed in a service center to correct earlier models. The ROMs in later models were modified to correct this.

Expansion interface

The TRS-80 did not use the S-100 bus like other Z80-based computers.[9] A proprietary Expansion Interface (E/I) provided several features: the ability to expand up to 48K of RAM, a floppy disk controller, a real-time clock, a second cassette port, an RS-232 port (as an option) and a Centronics parallel printer port.[32]

Originally, one could not print from the Model I without purchasing an Expansion Interface. However, Tandy Corp. soon sold a printer-only Interface for the Model I for approx. DM300 in Germany.

The Expansion Interface was the most troublesome part of the TRS-80 system. It went through several revisions. A pre-production version is said to have looked completely different, and to have had a card cage. Its edge card connectors tended to oxidise due to the use of two different metals in the contacts, and required periodic cleaning with a pencil eraser. The expansion unit required a second power supply, identical to the base unit power supply; an interior recess held both power supplies.

InfoWorld compared the cable spaghetti connecting the TRS-80's various components to the snakes in Raiders of the Lost Ark.[29] Since the cable connecting the expansion interface carried the system bus, it was kept short (about two inches). This meant that the user had no choice but to place it directly behind the computer with the monitor on top of it. This caused problems if one owned a monitor whose case did not fit the mounting holes. Also, the loose friction fit of the edge connector on the already short interconnect cable created the precarious possibility of disconnecting the system bus from the CPU if either unit happened to be moved during operation.

Floppy disk drives

Radio Shack did not offer a floppy disk drive for the TRS 80 until 1978. To use the Model I with a disk operating system,[32]:14–15 one had to buy the Expansion Interface, which included a single density floppy disk interface (formatted capacity of 85k). This was based on a Western Digital 1771 single density floppy disk controller chip. Four floppy drives could be used with the Model I in a daisy-chain.

Although demand for Model I drives greatly exceeded supply at first,[30] since the interface lacked a separate external data separator, it was very unreliable in practice.[29] Much of the unreliability was due to bugs in Radio Shack's early version(s) of TRS-DOS. The 1771 could not report its status for a short interval (several instruction cycles) after it received a command. A common method of handling this was to issue a command to the 1771, perform several "NOP" instructions, then query the 1771 for command status. Early TRS-DOS neglected to use the required wait period, instead querying the chip immediately after issuing a command, and thus false status was often returned to the OS, causing various errors and crashes. If the 1771 was handled correctly by the OS, it was actually fairly reliable.

In 1981 Steve Ciarcia published in BYTE the design for a homemade, enhanced expansion interface with additional RAM and a disk controller for the TRS-80.[33]

A data separator and a double density disk controller (based on the WD 1791 chip) were made by Percom (a Texas peripheral vendor), LNW, Tandy and others. The Percom Doubler added the ability to boot and use Double Density Floppies (they provided their own modified TRSDOS called DoubleDOS), and included the Data Separator. The LNDoubler added the ability to read and write from 5¼" diskette drives for over 1.2 Mb of storage. Near the end of the Model I's lifespan in 1982, double-density drives became available for it.

All TRS-80 disk formats were soft-sectored with index-sync, and except for some very early Shugart drives (recognizable by their spiral-cam head positioner), all TRS-80 floppy drives were 40-track double-density models. The combination of 40 tracks and double-density gave a maximum capacity of 180 kilobytes per single-sided floppy disk. The use of index-sync meant that a "flippy disk" required a second index hole and write-enable notch. One could purchase factory-made "flippies". Some software publishers formatted one side for Apple systems and the other for the TRS 80. The early drives sold by Radio Shack were 35-track models with a 160 kb capacity.

Hard drive

Radio Shack introduced a 5 MB hard-drive unit for the TRS-80 Models I and III (and later Model 4) in 1983. The size of the unit was about the same as a modern desktop computer enclosure. The initial retail price (US$2495) is equivalent to US$5900 in 2019.


One unusual peripheral offered was a "Quick Printer", an electrostatic rotary printer that scanned the video memory through the same bus connector used for the expansion interface, and printed an image of the screen onto aluminum-coated paper in about a second.[32]:16 Unfortunately, it was incompatible with both the final, buffered version of the expansion interface, and with the "heartbeat" interrupt used for the real-time clock under Disk BASIC. This could be overcome by using special cabling, and by doing a "dummy" write to the cassette port while triggering the printer.

Two other printers were offered: one for 57 mm metal coated paper, selling for approximately DM600 in Germany, and one built by Centronics for normal paper, costing at first DM 3000, later sold at approximately DM1500 in some stores. It had only 7 pins, so letters with descenders such as lowercase "g" did not reach under the baseline, but were elevated within the normal line.



Three versions of the BASIC programming language were produced for the Model I. Level I BASIC fit in 4 KB of ROM, and Level II BASIC fit into 12 KB of ROM. Level I was single precision only and had a smaller set of commands. Level II introduced double precision floating point support and had a much wider set of commands. Level II was further enhanced when a disk system was added, allowing for the loading of Disk BASIC.[9]

Level I Basic was based on Li-Chen Wang's free Tiny BASIC, additional functions added by Radio Shack.[13] It had an excellent manual[9] written by David Lien, which presented lessons on programming with text and humorous graphics, making the subjects very easy to understand. Lien wrote that it was "written specifically for people who don't know anything about computers ... I want you to have fun with your computer! I don't want you to be afraid of it, because there is nothing to fear ..."[17] Level I BASIC had only two string variables (A$ and B$), 26 numeric variables (A - Z) and one array, A(). Code for functions like SIN(), COS() and TAN() was not included in ROM but printed at the end of the book. The only error messages were: "WHAT?" for syntax errors, "HOW?" for arithmetic errors such as division by zero, and "SORRY" for out of memory errors.

Level I BASIC was not tokenized—reserved words were stored literally. In order to maximize the code that could be crammed into 4K of memory users could enter abbreviations for reserved words. For example, writing "P." instead of "PRINT" thus saving 3 bytes.

Level II BASIC was licensed from Microsoft. It was a cut-down version of the 16 KB Extended BASIC, since the Model I had 12 KB of ROM space. The accompanying manual was not nearly as colorful and suited for beginning programmers as the Level I BASIC manual. Original Level I BASIC-equipped machines could be retrofitted to Level II through a ROM replacement performed by Radio Shack for a fee (originally US$199). Users with Level I BASIC programs stored on cassette had to convert these to the non-tokenized Level II BASIC before use. A utility for this was provided with the Level II ROMS.

Disk BASIC added the ability to perform disk I/O, and in some cases (NewDos/80, MultiDOS, DosPlus, LDOS) added powerful sorting, searching, full screen editing, and other features. Level II BASIC reserved some of these keywords and issued a "?L3 ERROR", suggesting a behind-the-scenes change of direction intervened between the creation of the Level II ROMs and the introduction of Disk BASIC.

Microsoft also marketed a tape-cassette based enhanced BASIC called Level III BASIC. This added most of the functions in the full 16 KB version of BASIC.

Other applications

Blackjack and backgammon came with the TRS-80 for free, and at its debut Radio Shack offered four payroll, personal finance, and educational programs, all on cassette.[9][19]:3 While Radio Shack franchise stores sold third-party products, company-owned stores were at first prohibited from reselling products not sold by Radio Shack itself.[34] Its own products' quality was often poor. A critical 1980 80 Micro review of a text adventure described it as "yet another example of Radio Shack's inability to deal with the consumer in a consumer's market". The magazine added, "Sadly, too, as with some other Radio Shack programs, the instructions seem to assume that the reader is either a child or an adult with the mentality of a slightly premature corned beef."[35]

Green stated that year that although "there are more programs for the 80 than for all other systems combined" because of the computer's large market share, "Radio Shack can't advertise this because they are trying as hard as they can to keep this fact a secret from their customers. They don't want the TRS-80 buyers to know that there is anything more than their handful of mediocre programs available", many of which "are disastrous and, I'm sure, doing tremendous damage to the industry".[36][37] By 1982 the company admitted—after no software appeared for the Model 16 after five months—that it should have, like Apple, encouraged third-party developers of products like the killer app VisiCalc.[38] (A lengthy 1980 article in a Tandy publication introducing the TRS-80 version of VisiCalc did not mention that the spreadsheet had been available for the Apple II for a year.[39]) A full suite of office applications nonetheless became available from the company and others, including the VisiCalc and Multiplan spreadsheets and the Lazy Writer, Electric Pencil, and Scripsit word processors.

Despite the TRS-80's limited graphics and sound capability, independent software companies such as Big Five produced unlicensed versions of arcade games like Namco's Galaxian, Atari's Asteroids, and Exidy's Targ.[31] Some companies ported games from other home computers of the era, such as the original Zork adventure game. There were also many games unique to the TRS-80, including shooters like Cosmic Fighter and Defence Command and strange experimental programs such as Dancing Demon,[40] a game in which the player composed a song for a devil and choreographed his dance steps to the music.[41] Microchess for the Model I had three levels of play and could be run in the 4kb of memory that was standard with this model.

Utility software such as Stewart Software's Toolkit offered the first sorted directory, decoding or reset of passwords, and the ability to eliminate parts of TRS-DOS that were not needed in order to free up floppy disk space. They also produced the On-Line 80 BBS, a TRS-DOS based Bulletin Board System.

By 1982 perhaps more operating systems existed for the TRS-80 than for any other computer.[42] TRS-DOS—Radio Shack's operating system for its TRS-80 computers—had significant limitations, opening the market for various alternative OSes, including NewDOS, a third-party rival sold by a company called Apparat Personal Computers, which went out of business in 1987. Others included DoubleDOS, DOSPlus, MicroDOS, NEWDOS/80, UltraDOS (later called Multidos), and VTOS. The last versions (6.x) of TRSDOS were actually renamed LS-DOS (aka LDOS).

CP/M became a standard OS for business use on Z80-based machines, and versions ran on all TRS-80s. Omikron Systems' Mappers board remapped the BASIC ROM to run unmodified CP/M programs on the Model I.[43]


Dan Fylstra, among the first owners, wrote in BYTE in April 1978 that as an "'appliance' computer ... the TRS-80 brings the personal computer a good deal closer to the average customer", suitable for home and light business use. He concluded that it "is not the only alternative for the aspiring personal computer user, but it is a strong contender."[17] Jerry Pournelle wrote in 1980 that "the basic TRS-80 is a lot of computer for the money. It comes ready to run right out of the box, and it can be set up by three boys – ages 9, 11, and 13 ... The Tandy/Radio Shack documentation is excellent, and there are a lot of good programs available". He noted that while "just about every component of my TRS-80 has taken a trip to the local store to be fixed", "none of that cost me anything; it wasn't even inconvenient, especially with local Radio Shacks all over the place ... Given the price of the TRS-80, Tandy's quality control is better than you'd expect." Pournelle criticized the quality of Tandy's application and system software—including the "needlessly complex" TRSDOS—and high cost of its peripherals. He reported, however, that with the Omikron board, additional memory, and 8- and 5 1/4-inch disk drives, "for a total cost of under $5000, you have a 48 K-byte machine capable of running all the TRS-80 programs, CP/M software, and top-grade text editors like Word Master, Magic Wand, Electric Pencil, and the Proteus editor ... all without building a single kit".[43]

Compatible successors

For all uses of the "TRS-80" name, including machines technically unrelated to the Models I, III and 4, see List of TRS-80 and Tandy-branded computers.

Tandy would go on to replace the Model I with the broadly compatible Model III in 1980. (The TRS-80 Model II had been an entirely different and incompatible design). The Model III was in turn succeeded by the backward-compatible Model 4 in 1983.

Model III

In July 1980 Tandy released the TRS-80 Model III. The improvements of the Model III over the Model I included built-in lower case, a better keyboard, elimination of the cable spaghetti, 1500-baud cassette interface, and a faster (2.03 MHz) Z-80 processor. Shortly after, Model I production was discontinued as it did not comply with new FCC regulations as of January 1, 1981 regarding electromagnetic interference.[18][29][44][6]

The Model III could run about 80% of Model I software, but used an incompatible disk format.[18] Customers and developers complained of bugs in its BASIC and the TRSDOS operating system.[45] The computer also came with the option of integrated disk drives.

InfoWorld approved of the Model III's single-unit design, simplified cable management, and improvements such as lack of keyboard bounce and improved disk reliability. The reviewer, a former Model I owner, stated "I'm impressed" and that "had the Model III been available, it's probable that I wouldn't have sold it". He concluded, "If you're looking for a computer that's not too expensive but that performs well, you would be wise to test the Model III—you might end up buying it."[29]

Model 4

File:TRS-80 Model 4 (modified).jpg
TRS-80 Model 4 (standard version)

The successor to the Model III was the TRS-80 Model 4 (April 1983, with "4" written as an Arabic numeral), which included the capability to run CP/M. It had faster Z80A 4 MHz CPU[46] and was completely compatible with Model III software. A diskless version cost $999, with one disk drive $1699, and two drives $1999; an upgrade for Model III owners cost $799 and provided a new motherboard and keyboard.[47] Tandy sold 71,000 in 1984.[48]

Running CP/M had previously only been possible via a hardware modification that remapped the BASIC ROMs away from memory address zero, such as the third-party add-on sold as the Omikron Mapper board, or by running a version of CP/M modified to run at a starting address other than zero. However, this also required modified applications, since the area of memory at zero contained the vectors for applications to access CP/M itself.

The Model 4 shipped with TRSDOS 6, an enhanced version of the popular LDOS (itself an enhancement to older versions of TRSDOS) by Logical Systems. When the Model 4 boots into TRSDOS 6 the video display switches into 80×24 mode and the entire 64KB address space is mapped as RAM. The Model 4 is also capable of running all Model III software when a Model III operating system disk is detected and loaded during bootup, with a 64×16 video mode and Model III ROMs mapped from address zero. Model 4 features, including the internal speaker, are unavailable in Model III mode.[47]

The Model 4 also has the ability to display 640×240 or 512×192 high-resolution monochrome graphics with an optional board. A "luggable" version known as the Model 4P (1983) is a self-contained unit with a case design similar to that of a portable sewing machine.

Early versions of the Model 4 mainboard were designed to accept a Zilog Z800 16 bit CPU upgrade board to replace the Z80 8 bit CPU but this option was never released.

BYTE in October 1983 noted the lack of native software for the Model 4 but praised its backwards compatibility and TRSDOS 6's new features. The magazine concluded that the Model 4 "provides a lot of flexible computing power ... Radio Shack has a guaranteed winner".[47]


File:DGT-100 Brazilian TRS-80 Clone.jpg
TRS-80 Model I clone, the DGT-100 by DIGITUS Ind. Com. Serv. de Eletrônica Ltda.

Many clones of the TRS-80 Model I came on the market: the Lobo Max-80 (Lobo also produced their own version of the Expansion Interface), the LNW-80 Models I/II and Team computers (LNW also produced an alternate version of the Expansion Interface), and the Dutch Aster CT-80, a computer that could run both TRS-80 and CP/M software, and also had all the improvements of the later Model III.

EACA in Hong Kong made a Model I clone that was marketed around the world under different names with modifications. In Australia and New Zealand it was the Dick Smith System 80, in North America it was PMC-80 and PMC-81, in Hungary the HT-1080Z, in South Africa the TRZ-80, and in Western Europe it was Video Genie. The expansion bus was different and EACA also made its own Expansion Interface to fit it. There were several versions, and it was later split into a 'home' and a 'business' version, Genie I and II, and System-80 Mark I and II, where the II would have a numeric keypad instead of the built-in cassette player. EACA's Colour Genie was also based on TRS-80 Model I but with improved graphics and other changes, reducing its compatibility.

In Brazil several manufacturers developed clones for models I/III/IV. Dismac series D8000/D8001/D8002 (all three Model I clones) were the first personal computers manufactured in industrial scale in South America. Digitus made the DGT-100 and DGT-1000, Prológica made the highly successful CP300 and CP500 series (both Model III clones), Sysdata Eletrônica Ltda. made the Sysdata Jr. Prologica also made the CP400 / CP 400II which were copies of the TRS-80 Color Computer, with the external case being almost a copy of the Timex Sinclair 2068.

In Germany, S.C.S. GmbH in Mörfelden-Walldorf offered the Komtek-I Model I clone. Noteworthy was its four relay switching outputs.

In the Soviet Union, some ideas from the TRS-80 were used in development of the Корвет (Corvette) home/school computer.

See also


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  28. ^ "John Freire audio interview discussing the use of an AM radio for game sounds on the Model I". Retrieved July 20, 2010. 
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  40. ^ Dancing Demon
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External links