TRS-80

For the Chicago-based electronica group, see TRS-80 (group).

TRS-80 Model I with Expansion Interface
Type	Home computer
Release date	August 3, 1977 (1977-08-03)
Discontinued	January 1981
CPU	Zilog Z80 @ 1.78 MHz
Memory	4 KB ~ 48 KB

TRS-80 was Tandy Corporation's desktop microcomputer model line, sold through Tandy's Radio Shack stores in the late 1970s and early 1980s. 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 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. 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 $600. The pre-release price was $500 and a $50 deposit was required, with a money back guarantee at time of delivery. One major drawback of the original system was the massive RF interference it caused in surrounding electronics. Stricter FCC regulations on interference lead to the Model I's replacement by the Model III.

By 1979, the TRS-80 had the largest available selection of software in the microcomputer market.^{[citation needed]}

The Model I

History

In the mid-1970s, Radio Shack was a successful American chain of electronics stores. After Don French, a buyer for the company, purchased a MITS Altair kit computer, he began designing his own and showed it to vice president of manufacturing John V. Roach. Although Roach was unimpressed, Radio Shack hired Steve Leininger from National Semiconductor to evaluate French's design, and they began working together in June 1976. The company envisioned a kit, but Leininger—who had worked at early computer store Byte Shop—persuaded the others that because "too many people can't solder", a preassembled computer would be better.

Despite internal opposition to selling a microcomputer, as the popularity of CB radio—at one point more than 20% of Radio Shack's sales—declined, the company sought new products. In December 1976 French and Leininger received official approval for their project but were told to emphasize cost; for example, leaving out lowercase characters saved $1.50 in components and reduced the retail price by $5. In February 1977 they showed their prototype, running a simple tax-accounting program, to Charles Tandy, head of Radio Shack's parent Tandy Corporation. The program quickly crashed as the computer could not handle the $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. French suggested that the company could sell 50,000 computers, but more skeptical executives disagreed and suggested 1,000 to 3,000 per year at the target $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.

Radio Shack announced the TRS-80 (Tandy Radio Shack) at a New York City press conference on August 3, 1977. It cost $399, or $599 with a 12" monitor and a Radio Shack tape recorder as datacassette storage. Before this, the most expensive product Radio Shack sold was a $500 stereo. The company hoped that the new computer would help Radio Shack move into higher-priced products, and improve its "schlocky" image among customers. Small businesses were the primary target market, followed by education, then consumers and hobbyists. Despite its hobbyist customer base, Radio Shack saw hobbyists as "not the mainstream of the business". Although the press conference did not receive much media attention due to a terrorist bombing elsewhere in the city that day, "six sacks of mail" arrived at company headquarters asking about the computer, and over 15,000 people called Tandy to purchase a TRS-80, paralyzing its switchboard. Unlike competitor Commodore—which had announced its PET several months earlier but had not yet shipped any—Radio Shack began shipping computers by September. Still forecasting 3,000 sales a year, the company 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.

Roach became Tandy's CEO in 1981, Leininger became its director of strategic planning, and French founded a software company. Although selling computers did not change Radio Shack's image and its executives disliked the "Trash-80" nickname for its products, by 1984 computers accounted for 35% of its sales, and the company had 500 Tandy Radio Shack Computer Centers.

Hardware

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.

Keyboard

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. 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

The TRS-80 was accompanied by a white-on-black display, which was a modified RCA XL-100 black and white television. The color of the screen text was 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.

Layout of characters and pixels on the TRS-80 display

The video hardware could only display text at 64 or 32 characters wide by 16 lines of resolution. This was because the video memory system used a single kilobyte of video memory. Seven of the bits of each byte were 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) could be displayed because the upper 64 characters of the 128 character set displayed as a grid of 2×3 blocks (very similar to Teletext). BASIC routines were provided which could write directly to this 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, one 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.

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 1 had no sound hardware. Square wave tones could be produced by outputting data to the cassette port and plugging headphones or an amplifier into the Data Out line. Some games used this ability for sound effects.

Cassette tape drive

User data was originally stored on cassette tape. Radio Shack's model CTR-41 cassette recorder was included with the $599 package. The cassette tape interface was very slow and erratic; it was sensitive to audio volume changes, and the machine only gave 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 (25 bytes per second); Level II BASIC doubled this to 500 bits per second (50 bytes per second). Some programmers wrote machine language programs that would increase the speed to up to 1500 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 two states, creating squarewave 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. A proprietary Expansion Interface (E/I) provided several important 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.

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. 300 Deutschmark 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.

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. One reviewer compared the resulting collection of wires connecting the TRS-80's various components to the snakes in Raiders of the Lost Ark.

Floppy disk drives

Radio Shack did not offer a floppy drive for the TRS 80 until 1978. To use the Model I with a disk operating system, 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.

Since the interface lacked a separate external data separator, it was very unreliable in practice. 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.

Double-density floppy disks

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 8" diskette drives for over 1.2mb of storage. Near the end of the Model I's lifespan in 1982, double-density drives became available for it.

Double-sided floppy disks

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. However, the use of index-sync meant that a "flippy disk" required a second index hole and write-enable notch. One could also purchase factory-made "flippies", or format the back side for Apple systems (as some software publishers of the era did).

The drives sold by Radio Shack were 35-track models with a 160K capacity.

Hard drive

Radio Shack introduced a 5MB hard-drive unit for the TRS-80. The size of the unit was about the same as a modern desk-top computer enclosure. The unit had a list retail price of approximately $1500.

Printers

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. 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 600 Deutschmark in Germany, and one built by Centronics for normal paper, costing at first 3000 Deutschmark, later sold at approximately 1500 Deutschmark 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.

BASIC

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.

Level I Basic was based on Li-Chen Wang's free Tiny BASIC, additional functions added by Radio Shack. It achieved a measure of noteworthiness due in large part to its outstanding manual, written by David Lien, which presented lessons on programming with text and humorous graphics, making the subjects very easy to understand. It 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 $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 recognized some of these commands and issued a "?L3 ERROR", suggesting that a behind-the-scenes change of direction intervened between the recording 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.

Software 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. Many leading developers, and independent software companies such as Big Five, produced unlicensed versions of popular arcade hits like Namco's Pac-Man and Galaxian, Atari's Centipede, Exidy's Targ and Stern Electronics' Berzerk (with digitized speech). 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, which was not strictly speaking a game but did have significant entertainment value.

A full suite of office applications were also available, including the VisiCalc and As-Easy-As spreadsheets and the Lazy Writer, Electric Pencil and Scripsit word processors.

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.

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, LDOS, 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 all TRS-80s got versions of it. However, the Model I's CP/M proved largely useless since the computer had its video memory in the normal location where the OS loaded. This meant that CP/M software had to be explicitly rewritten for the Model I, destroying its main advantage of portability (normally CP/M applications such as WordStar could be interchanged between different incompatible machines with a configuration program being used to set up things such as the video display format).

Clones

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, Prologica 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- Waldorf 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.

Business systems

Tandy 10

Main article: Tandy 10 Business Computer System

Tandy's first design for the business market was a desk-based computer known as the Tandy 10 Business Computer System, which was released in 1978 but quickly discontinued.

Model II and 12

TRS-80 Model II

In October 1979, Tandy began shipping the Model II, which was targeted to the small-business market. Creative Computing in 1984 called it a "state-of-the-art business machine" that "might have taken the business market by storm had it not had a nameplate reading 'Radio Shack.'"

The Model II was not an upgrade of the Model I, but an entirely different system. As a professional business machine, it used state-of-the-art hardware and had numerous features not found in the primitive Model I such as DMA, vectored interrupts, a detachable keyboard, and port instead of memory-mapped I/O. It sported 80x25 text and a singled-sided 500k 8" floppy drive, and either 32 or 64k of RAM, along with two RS-232 ports and a Centronics-standard parallel port. The video memory was not mapped into the main address space or directly accessible by the CPU (only through indirect register writes). Unlike most computers, it had no BIOS ROM except a small boot loader (the BIOS was loaded off the boot floppy). Because of this and the use of port I/O, almost all of the Model II's memory could be used by software. The Model II ran the TRSDOS operating system (renamed to TRSDOS-II starting with version 4.0) and BASIC. TRSDOS for the Model II was not compatible with TRSDOS for the Model I; thus the Model II never had the same breadth of available software as the Model I (a situation aggravated by the fact that Tandy discouraged third-party software development^{[citation needed]}). This was somewhat mitigated by the availability of the CP/M operating system for the Model II from third parties such as Pickles & Trout. Three internal expansion slots could be used for add-on cards such as additional serial ports and a video board that allowed bitmap graphics. Since the Model II did not boot into BASIC (which was provided on disk), it had a more professional feel to it than some machines such as the Commodore PET^{[citation needed]} (which may have failed in the business market partially because of its using BASIC as an OS^{[citation needed]}).

Tandy offered a desk custom-designed for the Model II for US$370. It could hold an additional three 8" disk drives or up to four 8.4MB hard drives (the Model II allowed three external floppy drives to be daisy-chained to it).

The Model II was replaced in 1982 by the Model 12, which used half-height ("thinline") double-sided floppy drives, and integrated most of the Model II electronics into a single main board. The video/keyboard card plugged into a single slot in the main board. An expansion card cage was available as an option, allowing more plug-in cards. The Model 12 was essentially a Model 16B (described below) without the Motorola processor, and could be upgraded to a Model 16B.

Model III

TRS-80 Model III

In July 1980 Tandy released the Model III. The improvements of the Model III over the Model I included built-in lower case, a better keyboard, 1500-baud cassette interface, and a faster (2.03 MHz) Z-80 processor. With the introduction of the Model III, Model I production was discontinued as it did not comply with new FCC regulations as of 1 January 1981 regarding electromagnetic interference. 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.

The Model III could run about 80% of Model I software, but used an incompatible disk format. Customers and developers complained of bugs in its BASIC and the TRSDOS operating system. The computer also came with the option of integrated disk drives. Since they took power from the same supply as the motherboard and screen, which was not upgraded for the disk drive models, it was common to see the screen image shrink noticeably during drive access.

Model 4

The successor to the Model III was the Model 4 (April 1983, with "4" written as an Arabic numeral), which included the capability to run CP/M.

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 also added an 80 column by 24 line video display mode required for CP/M compatibility.

The Model 4 shipped with TRSDOS 6, an enhanced version of LDOS by Logical Systems and a vastly superior operating system to Tandy's earlier TRSDOS offerings. When the Model 4 booted into TRSDOS 6 the video display switched into 80×24 mode and the entire 64KB address space was mapped as RAM. The Model 4 was also capable of running all Model 3 software when a Model 3 operating system disk was detected and loaded during bootup with a 64×16 video mode and Model 3 ROMs mapped from address zero.

TRS-80 Model 4P

The Model 4 also had 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) was 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 Z8000 16 bit CPU upgrade board to replace the Z80 8 bit CPU but this option was never released.

Model 16, Model 16B, and Tandy 6000

Tandy later released the TRS-80 Model 16, as the follow-on to the Model II; an upgrade kit was available for Model II systems. The Model 16 added a 6 MHz, 16-bit Motorola 68000 processor and memory card, keeping the original Z-80 as an I/O processor. It had two half-height ("thinline") double-sided 8-inch floppy drives, though the Model II upgrade did not replace the floppy drive. It could run either TRSDOS-16 or Xenix, Microsoft's version of UNIX. Of the two operating systems, Xenix was far more popular. TRSDOS-16 was essentially a layer of code providing a 68000 interface to Model II TRSDOS, with no additional features and little compatible software. 68000 functionality was added as an extension, loading 68000 code into the 68000 memory via a shared memory window with the Z80.

Xenix, on the other hand, offered the full power of UNIX System III including multi-user support. The Model 16 family with Xenix became a popular system for small business, with a relatively large library of business and office automation software for its day. Tandy offered multi-user word processing (Scripsit 16), spreadsheet (Multiplan), and a 3GL "database" (Profile 16, later upgraded to filePro 16+), as well as an accounting suite with optional COBOL source for customization. RM-COBOL, Basic, and C were available for programming, with Unify and Informix offered as relational databases. A kernel modification kit was also available.

TRS-Xenix was notable for being a master/slave implementation, with all I/O being performed by the Z80 while all processing was done within the otherwise I/O-free 68000 subsystem.

The Model 16 evolved into the Model 16B, and then the Tandy 6000 HD, gaining an internal hard drive along the way and switching to an 8 MHz 68000. Tandy offered 8.4MB, 15 MB, 35 MB, and 70 MB external hard drives, up to 768 KB of RAM, and up to six additional RS-232 serial ports supporting multi-user terminals. Additional memory and serial port expansion options were available from aftermarket companies.

Internal variants of the Model 16 architecture were built running at speeds in excess of 10 MHz, 68010 processors, up to 8Mb of RAM, SCSI disk interfaces, and up to 12 RS-232 ports.^{[citation needed]}

Other systems

Color Computers

Main article: TRS-80 Color Computer

Tandy also produced the TRS-80 Color Computer (CoCo), based on the Motorola 6809 processor. This machine was clearly aimed at the home market, where the Model II and above were sold as business machines. It competed directly with the Commodore 64, Apple II, and Atari 8-bit family of computers. OS-9, a multitasking, multi-user operating system was supplied for this machine.

Model 100 line

Main article: TRS-80 Model 100

In addition to the above, Tandy produced the TRS-80 Model 100 series of laptop computers. This series comprised the TRS-80 Model 100, Tandy 102, Tandy 200 and Tandy 600. The Model 100 was designed by the Japanese company Kyocera with software written by Microsoft. (The Model 100 firmware was the last Microsoft product to which Bill Gates was a major code contributor.)

The Model 100 had an internal 300 baud modem, built-in BASIC, and a limited text editor. It was possible to use the Model 100 on essentially any phone in the world with the use of an optional acoustic coupler that fit over a standard telephone handset. The combination of the acoustic coupler, the machine's outstanding battery life (it could be used for days on a set of 4 AA batteries), and its simple text editor made the Model 100/102 popular with journalists in the early 1980s. The Model 100 line also had an optional bar code reader, serial/RS-232 floppy drive and a Cassette interface.

Also available as an option to the Model 100 was an external expansion unit supporting video and a 5¹⁄₄" disk drive, connected via the 40-pin expansion port in the bottom of the unit.

Tandy 200

Tandy 200 beside a Sony Vaio laptop

The Tandy 200 was introduced in 1984 as a higher-end complement to the Model 100. The Tandy 200 had 24 KB RAM expandable to 72 KB, a flip-up 16 line by 40 column display, and a spreadsheet (Multiplan) included. The Tandy 200 also included DTMF tone-dialing for the internal modem. Although less popular than the Model 100, the Tandy 200 was also particularly popular with journalists in the late 1980s and early 1990s.

MC-10

Main article: TRS-80 MC-10

The MC-10 was a short-lived and little-known Tandy computer, similar in appearance to the Sinclair ZX81.

It was a small system based on the Motorola 6803 processor and featured 4 KB of RAM. A 16 KB RAM expansion pack that connected on the back of the unit was offered as an option as was a thermal paper printer. A modified version of the MC-10 was sold in France as the Matra Alice.

Programs loaded using a cassette which worked much better than those for the Sinclair.^{[citation needed]} A magazine was published which offered programs for both the CoCo and MC-10 but very few programs were available for purchase. Programs for the MC-10 were not compatible with the CoCo.

A PC-2 ready for use

Pocket Computers

Main article: Tandy Pocket Computer

The TRS-80 brand was also used for a line of Pocket Computers which were manufactured by Sharp or Casio, depending on the model.

PC-compatible computers

In the early 1980s, Tandy began producing a line of computers that were "DOS compatible": able to run MS-DOS and certain applications, but not fully compatible with every nuance of the original IBM PC systems. The first of these was the Tandy 2000, followed later by the less expensive Tandy 1000. As margins decreased in PC clones, Tandy was unable to compete and stopped marketing their own systems.

Originally, Tandy offered computers manufactured by Tandon Corporation, and then started producing their own line of systems.^{[citation needed]}

The Tandy 2000 system was similar to the Texas Instruments Professional Computer in that it offered better graphics, a faster processor (80186) and higher capacity disk drives (80 track double sided 800k 5.25 drives) than the original IBM PC

However, around the time of its introduction, the industry began moving away from MS-DOS compatible computers and towards fully compatible clones; later Tandy offerings moved toward full PC hardware compatibility.

The later Tandy 1000 systems and follow-ons were also marketed by DEC, as Tandy and DEC had a joint manufacturing agreement.

Emulators

Emulators for the TRS-80 are listed below.

• Windows: HT1080Z EACA Emulator for Windows XP
• Windows: TRS32 Model 1/3/4 Emulator for Win XP (shareware)
• Windows/Linux/Mac:: M.E.S.S. Emulator includes TRS-80 emulator
• Windows/Linux/Mac: VirtualT Open source Model 100/102/200 Emulator
• Linux/Unix: xtrs (open-source)
• Java: Java applet
• Mac Classic: TRS-80 Emulator for Mac OS (no sound support) for Mac OS 7.5.5 or higher

See also

• Delimiterless input
• List of TRS-80 games
• List of TRS-80 software
• List of TRS-80 clones
• 80 Micro, magazine devoted to the TRS-80
• Creative Computing, pioneering Microcomputer magazine that catered to Atari, Apple, PET and TRS-80 users during their heyday
• SoftSide, magazine with BASIC programs for the TRS-80 and other microcomputers of the same era
• The Alternate Source Programmer's Journal, magazine with deeply technical programming articles, most of which were at the Assembly Language level, for the TRS-80.

External links

• TRS-80 at the Open Directory Project
• RadioShack Catalogs (1939-2005)
• TRS-80 and Tandy Computer Catalogs (1977-1992)
• TRS-80 and Tandy Computer TV Commercials (1980-85)
• TRS-80 and Tandy Computer TV Commercials (1986-89)
• 8bit-micro.com - TRS-80 Support Group and Online Magazine
• Radio Shack Model I and II catalog RSC-3
• trs-80.com : Ira Goldklang's TRS-80 Revived Site
• CoCo Central : TRS-80 Fan & Developer Site
• TRS-80 Model 1 at www.old-computers.com
• REM 80 - The North West TRS-80 USers Group Magazines