The TRS-80 Micro Computer System (TRS-80, later renamed 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, Z80 [microprocessor]. It is one of the earliest mass-produced and mass-marketed retail home computers.The TRS-80 has a full-stroke QWERTY keyboard, the Zilog Z80 processor, 4 KB dynamic random-access memory (DRAM) standard memory, small size and desk area, floating-point Level I BASIC language interpreter in read-only memory (ROM), 64-character per line video monitor, and a starting price of US$600 (equivalent to US$2,700 in 2021). A cassette tape drive for program storage was included in the original package.

While the software environment was stable, the cassette load/save process combined with keyboard bounce issues and a troublesome Expansion Interface contributed to the Model I's reputation as not well-suited to serious use. It lacked support for lowercase characters, which also hampered business adoption.

An extensive line of upgrades and add-on hardware peripherals for the TRS-80 was developed and marketed by Tandy/Radio Shack. The basic system can be expanded with up to 48 KB of RAM (in 16 KB increments), and up to four floppy disk drives and/or hard disk drives. Tandy/Radio Shack provided full-service support including upgrade, repair, and training services in their thousands of stores worldwide.

By 1979, the TRS-80 had the largest selection of software in the microcomputer market. Until 1982, the TRS-80 was the best-selling PC line, outselling the Apple II series by a factor of five according to one analysis.In mid-1980, the broadly compatible TRS-80 Model III was released. The Model I was discontinued shortly thereafter, primarily due to stricter Federal Communications Commission (FCC) regulations on radio-frequency interference to nearby electronic devices. In April 1983, the Model III was succeeded by the compatible TRS-80 Model 4.

Following the original Model I and its compatible descendants, the TRS-80 name became a generic brand used on other unrelated computer lines sold by Tandy, including the TRS-80 Model II, TRS-80 Model 2000, TRS-80 Model 100, TRS-80 Color Computer, and TRS-80 Pocket Computer.

Tandy Corporation was an American family-owned leather goods company based in Fort Worth, Texas, United States. Tandy Leather was founded in 1919 as a leather supply store. By the end of the 1950s, under the tutelage of then-CEO Charles Tandy, the company expanded into the hobby market, making leather moccasins and coin purses, making huge sales among Scouts, leading to a fast growth in sales.Entering the 1960s, aiming to broaden the company horizon, Charles Tandy acquired a number of craft retail companies, including RadioShack in 1963, then an almost bankrupt chain of electronics stores in Boston.

In the 1980s, now led by John Roach as CEO, the corporation started to invest into the personal computer market, being one of the pioneers in the personal computer race, being lauded by the magazine Financial World as “the driving force at the front-running company in the red-hot personal computer race.”In 2000, the Tandy Corporation name was dropped and the entity became the RadioShack Corporation.