Made in USA by Tandy Radio Shack in 1977
This platform includes:
TRS-80 Micro Computer System (AKA: TRS-80 Model I)
TRS-80 Model III
TRS-80 Model 4
TRS-80 Model 4P
TRS-80 Gate Array Model 4
TRS-80 Model 4D
Tandy 10 (special case)
Clones of this series

Any "TRS-80" branded machine not specifically mention here as compatible, are _not_ included in this platform. This includes the Model II, Tandy Color Computer series (Tandy Coco), MC-10, Model 100, Model 12, Model 16 series, Tandy 200, Tandy 1000, Tandy 2000, Tandy 6000, Tandy Pocket Computer series, Tandy Zoomer, and Tandy VIS.

Many clones were partially hardware compatible with the TRS-80 models. Some were not at all compatible.
  • Dick Smith System 80 (EACA botched legality, technically a pirate) [Model I]
  • EACA Video Genie (EACA botched legality, technically a pirate) [Model I]
  • EACA Video Genie II (EACA botched legality, technically a pirate) [Model I]
  • EACA Color Genie (EACA botched legality, technically a pirate) [enhanced Model I, color, not fully compatible]
  • Personal Micro Computers PMC 80 (EACA botched legality, technically a pirate) [Model I]
  • Personal Micro Computers PMC 81 (EACA botched legality, technically a pirate) [Model I]
  • HT-1080Z [Model I]
  • TRZ-80 (EACA botched legality, technically a pirate) [Model I]
  • LNW-80 (100% legit clone, also 100% IBM-PC compatible, 128×48x8 color mode, Intel [email protected]) [Model I/III]
  • Lobo Systems Max-80 ([email protected] 64/128/192KB RAM)
  • System-80 Mark I [Model I]
  • System-80 Mark II [Model I]
  • Dismac D8000 [Model I]
  • Dismac D8001 [Model I]
  • Dismac D8002 [Model I]
  • Digitus DGT-100 [Model I]
  • Digitus DGT-1000 [Model ?]
  • Prológica CP300 [Model III]
  • Prológica CP500 [Model III]
  • Sysdata Eletrônica, Sysdata Jr [Model ?]
  • SCS Komtek-I [Model ?]
  • Советский Корвет (Soviet Corvette) [8/16-bit Intel 8080 compatible CPU, not an exact clone of any one model]
  • Aster CT-80 (speaker sound, 4MHz CPU, Fully CP/M standardized) [Model I/III]
  • HBN Electronic, Le Guépard
  • Mera-Elzab, Meritum (Poland's 1st Home Computer. Buzzer sound) [Model I]
  • Mera-Elzab, Meritum II (256x192x4 graphics included, 512x192 monochrome, buzzer sound) [Model I]
  • Microcomputer Technology, MTI Mod III Plus
  • Pentasonic, PROF 80
  • Radionic R1001

  • Tandy 10 (Authorized Model I clone with an Intel 8080 CPU)

  • It should be noted that no customer was ever required to take apart their TRS-80, solder anything, or install any hardware alone. Radio Shack had a very poor reputation for quality control at the time, but many journalists noted how the TRS-80 and support was better than expected. Also, at the time, home computers only came as a kit requiring the user to solder things or were shockingly overpriced (Apple][). Radio Shack would do all of this free-of-charge for TRS-80 owners, even if it was not Radio Shack hardware.

    The TRS-80 (AKA:TRS-80 Micro Computer System, AKA: TRS-80 Model I) is a Z80 based personal computer. launched in 1977 that competed with the original Apple ][ and Commodore PET (and later the Atari 400 & 800, which is also out sold). It sold for the bargain price (at the time) of $399 barebones or $599 with monitor and cassette drive and was most expensive item Radio Shack had ever sold. Radio Shack expected to sell 1,000 units yearly or 3,000 at the very most. Word of the upcoming product was leaked to the press and 15,000 people called Radio Shack to buy one before it was even available to buy. It is know to be 15,000 people because this was the point at which Radio Shack's phone switchboard failed. After upgrading their PBX, 250,000 people pre-ordered. The Commodore PET was announced but not yet being manufactured. Manufacturing never managed to fill all the pre-orders and 200,000 units were sold with the remaining customers receiving later models. Various text books were included or part of the manual over the life of the TRS-80. They taught programming in various languages and/or other computer related things. The TRS-80 was discontinued in Jan 1st, 1981 due to FCC violations regarding electromagnetic interference.
    The TRS-80, by default, ran the Z80 at 1.774 MHz, had a maximum of 48 KB RAM, had only upper case text, and accessories all interfaced with ribbon cable or unwoven threads of cables ("spaghetti cables") to circuit card edge connectors. Memory expansion was also done with ribbon or spaghetti cables. A memory expansion require replacing multiple Programmable Array Logic chips, not just the memory. Later models used din-plugs except for the expansion port that remained edge-card. The different din plugs were all identical and the user needed to know the correct port. BASIC (based on Tiny BASIC) and a custom CP/M were included. BASIC was not tokenized ("GOSUB" took 5 bytes of memory, where a tokenized BASIC would store the command in memory as a code using only 1 byte). Most commands could be abbreviated to preserve the precious 4k alloted to a BASIC program (PRINT could be stated as P., saving 3 bytes). BASIC Level II was later included (and the first version renamed to Level I). BASIC Level II had more commands, double precision floating point functions. Despite being based on Level I BASIC, it was licensed from Microsoft. Units with Level I BASIC in the ROM could be upgraded with a ROM chip from Radio Shack. Disk BASIC, the last version, included enhanced disk usage via BASIC commands. The unscrupulously named "Level III BASIC" was made by Microsoft and based on Microsoft's Extended BASIC and could be purchased separately on a cassette. The expansion bus was S-100 compatible but also included a proprietary standard, "E/I, (Expansion Interface)". The E/I could expand the unit with 48K RAM, a floppy disk controller, a real-time clock, 2nd cassette port, RS-232 port and a Centronics parallel printer port. A TRS-80 expansion module was actually purchased with none of these each upgrade was then added by the user into the expansion module. A separate power supply that matched the set of components was required. Different components used different metals and would cause electrolysis on the TRS-80s motherboard. Users could buy adapters that used gold to isolate the components from electrolysis at the expansion, plate the expansion port themselves, or frequently clean it. The cabling for expansion units had to be short (especially for the clock unit). So units sat directly behind the main box with built-in keyboard. The units were shaped so that a TRS-80 monitor would mount on top. Though a TV or other monitor was an option, it might not sit properly on an expansion unit. Cabling to the TV or Monitor was also short by necessity (due to generated interference), so placing it somewhere else was really not an option. Floppy drives specifically for the unit were made available July 1978 and required an expansion unit with the floppy controller installed. Consumers deemed the drives to be very unreliable but this was due to a software issue in TRSDOS remedied by using any other operating system or upgraded TRSDOS. in 1983 a 5 MB hard-drive was made available from Radio Shack. The memory mapping of the system was primitive and quite non-standard. Whereas other systems might let you PRINT data to a file, the display, or a printer using similar processes, on the Model I, these were three very, very different tasks. The 64 keys of the keyboard were directly hard wired memory locations, this was like having a 64 button gamepad in an era when the most advanced computers could only recognize up to 3 keys being depressed simultaneously and only 1 key at a time on most systems. But this also required software to handle the keyboard buffer instead of hardware like most other systems (single-task CPU usage, key presses literally suspended execution for a moment). The hardware could not do floating-point math meaning it had to be done with software. The system was not compliant with CP/M standards and therefore a custom version of CP/M was created and _all_ CP/M applications had to be patched or ported (almost completely defeating the purpose of using CP/M). However, a hardware modification allowed regular Z80 CP/M and applications to run (what happened with non-CP/M apps on modified hardware?) The system also included a very limited TRSDOS ("Tris-dos"). Later operating systems were NewDOS, LDOS, MultiDOS, DoubleDOS, VTOS, LS-DOS, MicroDOS, UltraDOS, MER-DOS, and DOSPlus. NewDOS supported a wide variety of drives, single/double sided, many different capacities, and drives made for entirely different computer systems! The system could be upgraded to a Z80A, and later manufactured units used this CPU instead. The system was initially 4k later units being shipped with 16K (same price). The system used a somewhat unusual light-blue-on-dark-blue display (the dark blue was perceived as black) that was deemed to be easier on the eyes than amber, green, or white. Of course it also could be used with a Black and White TV or a color one. Though interference cause by the unit was much more distracting on a color TV. The interference radiating from the unit was so pervasive, that some games actually features sound. This was accomplished by tuning an AM radio to a particular frequency and setting it against the unit! (Not joking) Some games even had digitized voices! But eventually programmers decided that it was more proper to produce sound out of the cassette port (to be played by the cassette player or some other analog audio device). The TRS-80 does not allot enough memory to fill the entire screen with text at once. It used a text semigraphics mode where grpahics and text coulf be mixed to fill the entire screen with useful things up to 128×48 graphics and up to 16 lines of text (located on the screen somewhere). Blackjack, and Backgammon came with the TRS-80. Upon release, Radio Shack offered a cassette of 12 applications (payroll, personal finance, and educational programs). They were widely criticized for not offering any other software and forbidding Radio Shack franchises (including Computer Centers) from selling any other software.

    The TRS-80 Model II is an incompatible Z80 based system aimed at small business customers. A totally different system from the other TRS-80s. Probably gameless. This system was also not compliant with CP/M standards.

    The Tandy 10 was a business minded variant of the TRS-80 Model I with an Intel 8080 CPU, 48K RAM, 24x80 text, Two dual-sided 8" diskette drives, ADOS Disk Operating System, and Dartmouth BASIC (not MS-BASIC). Sold in 1978. Tandy also offered Fortran IV and Assembly Language packages for the system. Peachtree Accounting software was ported to the platform. As the platform had abysmal sales, The TRS-80 Model II was created to replace it. Tandy 10 specific games (if they exist) are also cpu-8080 games and should be tagged such. Note the z80 almost entirely duplicates an 8080 (on a machine code level compatibility) but adds features. Tandy 10 games will probably run on TRS-80 but TRS-80 probably wont run on Tandy 10. The Tandy 10 was discontinued in 1980.

    The TRS-80 Model III is a July 1980 replacement for the Model I (which was renamed at this time). Every feature was improved. 16KB, 32KB, or 48KB RAM. Most of the expansion unit features could now be installed inside the case (no breakout box required). Two disk drives could be added. A graphics card was offered (the first ever?) for up to 512x192 resolution. However, a memory expansion still require replacing multiple Programmable Array Logic chips, not just the memory. It was "80% compatible" with the Model I (said Tandy). Incompatibility arises from software that attempts low-level hardware access but this does not effect cassette and serial ports. Model III disks cannot be read by Model I systems (normally) but Model I disks can be read by Model IIIs. The introduction of Microsoft software (BASIC) produced many bugs. In response, Radio Shack freely offered many software workarounds and granted broad permissions to modify Model III systems and share solutions without voiding the warranty even if copyrighted works were involved (TRSDOS and Microsoft BASIC). This policy helped many 3rd party operating systems to be fully compatible with TRSDOS. In fact, 3rd party OS friendliness was one of factors of the IIIs design. The TRS-80 Model III was also discontinued in Jan 1st, 1981 for the same reasons as the Model I. The Model III was marketed as a "high-end" TRS-80. The case was silvery-gray.

    The TRS-80 Model 4 ("IV" was never used) had a Z80A rated at 4 MHz (about 3.5 MHz in reality) and coulf hold as much as 128KB RAM. A memory expansion still require replacing multiple Programmable Array Logic chips, not just the memory. TRSDOS 6 (LDOS). Cat No. 26-1069. It was fully CP/M standardized. Digital Research produced a Tandy/Radio Shack branded version of CP/M 3.0 but many users found vanilla CP/M 2.2 to be more stable. Montezuma Micro CP/M was a Model 4 optimized version of CP/M 2.2 and provided wide access to disks and drives similar to the way NewDOS had for Model I's. Any Model I or III software can be used but the system looks for a Model III operating system to boot in order to trigger the use of Model I or III text and graphics and memory management. The memory map was completely changed so that Z80 assembly applications actually worked like Z80 assembly applications. One could now PRINT to attached accessory (and the system would automatically print to file if the accessory was not found, so work was not lost and could later go from file to accessory once the accessory was working). The Model 4 had dedicated bank-switching Video RAM instead of taking a chuck of normal linear memory. A new graphics card allowed for 640×240 and 512×192 modes. The 640 x 240 did not use all the video RAM and the left over RAM could be used to render windows or store program data. These modes could be mixed with the built-in graphics and text modes. There was a real hardware buffer for the keyboard. Additional characters sets could be used (Greek and Symbol came with the system). Assembly code for Model Is or IIIs had to be ported to use any of the 4s new features (otherwise they could only run as I or III applications with the limitations of those systems). Applications on the Model 4 can be loaded into memory and stay suspend while one of them running. Initially this was only regarding BASIC applications but an application called DoubleDuty extended this feature to full task switching. An upgrade kit was offered that replaced the motherboard and keyboard in a Model III (the III and 4 used the same internal frame but a slightly different outer off-white case). It looked so similar that Radio Shack's catalog was amended to say, "Yes, it looks like a Model III, but it's much much more." The system can be upgraded to a Zilog Z800 16 bit CPU. Neither Radio Shack nor any other company ever produced such an upgrade kit. H.I. Tech produced the XLR8er that added an Hitachi [email protected] and 256K ramdisk. Since the HD64180 executed some Z80 code using fewer cycles, the performance was 25 to 30 percent faster than a [email protected] This CPU could be overclocked to 7MHz and programmers could access it's DMA channels for even better performance. A total of 384K RAM could be made available with this upgrade.

    The TRS-80 Gate Array Model 4 used Gate Array Programmable Array Logic chips where the The TRS-80 Model 4 used Programmable Array Logic chips. Cat No. 26-1069A. The previous models had wait states inserted into the circuitry to interface with the PAL chips. GAP chips do not require this so the machine actually runs at 4MHz. GAP chips allowed for a vast reduction in the number of chips, allowed manufacture of the 4 as a single-board computer, and reduced costs. It also meant that adding memory was a simple task of merely plugging in the memory instead of replacing multiple chips as was required by previous models. This also for the first time, made it easy for 3rd parties to produce memory upgrades an not have to rely on Radio Shack supplied memory. The Gate Array Model 4 is immediately distinguishable from the original Model 4 by it's green phosphor display and single cluster keyboard (no space between arrows, numeric pad); both of which fans hated.

    The TRS-80 Model 4P (Cat no. 26-1080) and later the TRS-80 Gate Array Model 4P (26-1080A). Sept 1983, was a luggable version of the Model 4 that lacked and Model III hardware. But, it came with a 'software' solution for Model III compatibility. Users would boot the "Model III ROM Image" to change the system into a Model III compatible computer. It would continue forever to be a Model III. The GAP 4P was discontinued in 1985 due to lackluster sales and strong sales of the desktop Gate Array Model 4.

    The Tandy TRS-80 Model 4D (26-1070) 1985 was the ultimate incarnation of the Model 4 designed to sell until 2011 or "until the marketplace tells us it is no longer a product". LS-DOS 6.3, Deskmate productivity suite, . Half height twist latched drives replaced the full height clamp latched drives and offered 378KB disk capacity. This computer was also to fulfill Tandy's many outstanding contracts with public school districts. It was updated in 1987 and improvements included double sided drives. It was discontinued in 1991 and the last one was sold in 1994.
    Hobbiests have upgraded the 4D to use a [email protected] and 256k dynamic RAM.

    From 1979 to 1982 the TRS-80 was the best-selling personal computer in the US. It out sold the Apple ][ Series by a factor of 5. It was a popular choice in schools and was the same price to schools as it was to the home user. Whereas the Apple units were and known to be considerably more expensive (schools received Apples through Apple's donation program). Students were generally given wide access to TRS-80s but Apples were restricted to oversupervised times and circumstances and generally only available to teachers and staff. Many of whom held a traditional view of learning that had no need of computers. Apple donations eventually overwhelmed TRS-80 purchases. When the Apple][e enhanced model upgrades and units began arriving, there was no need to spend money on TRS-80 4s or Tandy Cocos and the outdated Model Is and IIIs were phased out. A few TRS-80 Model 4Ds made it to schools where students could use them. Most Apples spent most of the time off and gathering dust.

    For various reasons, this series had the possibly undeserved moniker "Trash 80". Certainly the Model I was a short step of from a hobbyist kit with many quirks and quality issues (always fixed for free by Radio Shack), but the moniker was applied to the later III, 4, 4P, and 4D models without sufficient cause.

    The programming language known as "Snake" was developed for this computer.

    The Trisstick was an adapter produced and sold by Big Five Software. It allowed Atari compatible joystick to interface with TRS-80 Model I and III systems.

    The CHROMAtrs hardware upgrade used a TMS9918A graphics chip and 16k video RAM to add 256x192x16 color, 256x192x4 greyscale, and 40x24 color or greyscale text modes. It also introduced the capability of up to 32 sprites which could be rotated and scaled. It interfaced with the s-100 bus. And it included a joystick adapter compatible with the Trisstick.

    The Micromint E-Z Color also used a TMS9918A graphics chip to add 256x192x16 color mode and 32 sprites. The CHROMAtrs and E-Z Color are not software compatible (so games for one can't use the other).

    tech info

    resolution: 128 x 48 x 2 colors
    memory: 16K RAM, 1K VRAM, 4K ROM
    CPU: Z80 1.77 MHz
    sound: no sound

    Related systems

    Tandy Color Computer1980
    Tandy Zoomer1992