Tangerine Microtan 65

Origins and History

Tangerine Computer Systems was established in the United Kingdom during the late 1970s by Dr Paul Johnson and Barry Muncaster. They introduced the Microtan 65 in 1979 as a versatile and affordable microcomputer. It was initially sold as a bare printed circuit board or a kit of parts for home assembly. This approach appealed directly to the burgeoning electronics hobbyist community in Britain. The machine predates the massive boom of the 1980s home computer market and served as an important educational stepping stone. The founders of Tangerine would later use the experience gained from this modular system to develop the highly successful Oric-1 and Oric Atmos computers in the early 1980s.

Technical Specifications

The core of the machine was the ubiquitous MOS Technology 6502 microprocessor. This processor ran at a relatively modest clock speed of 750 kilohertz. The standard unexpanded single-board computer came equipped with just one kilobyte of Random Access Memory. It also featured one kilobyte of Read Only Memory containing the TANBUG system monitor programme. This system monitor allowed users to input machine code instructions directly into the memory locations using hexadecimal codes.

Video output was generated using discrete logic components rather than a dedicated video processor chip. The system provided a monochrome text display of 32 columns by 16 rows on a standard domestic television set. Users could also utilise a set of chunky graphics characters to create rudimentary visual displays and simple games.

The primary input method for the earliest models was a basic twenty-key hexadecimal keypad. This keypad allowed users to type in the raw memory addresses and data values required to programme the 6502 processor. Tangerine later offered a full alphanumeric keyboard to make typing significantly easier. Data storage was achieved by connecting a standard audio cassette recorder, allowing users to save and load their custom programmes onto magnetic tape.

System Expansion

The true power of the Tangerine system lay in its modular design. Users who outgrew the basic single-board setup could purchase a backplane known as the System Rack. This rack allowed the original board to be plugged in alongside various expansion cards. Tangerine and several third-party companies produced a wide array of expansions. Enthusiasts could buy memory expansion boards to increase the RAM capacity up to 32 kilobytes or more. High-resolution graphics boards were also available, enabling detailed mathematical plotting and more complex graphical displays. Further expansion options included serial interfaces, parallel ports, and eventually floppy disk drive controllers.

Common Uses and Applications

The machine was primarily an educational tool for learning assembly language and digital electronics. Hobbyists spent countless hours typing in hexadecimal codes from computing magazines to create simple games or utility programmes. The exposed expansion bus and well-documented hardware made it incredibly popular for interfacing with the outside world. Users built custom circuits to control model railways, monitor weather sensors, or automate simple electronic tasks around the home.

In the commercial and academic sectors, expanded rack-mounted versions of the machine were sometimes employed as cheap industrial controllers. University laboratories used them for data logging and process control experiments because they were significantly cheaper than dedicated industrial minicomputers. While it was never a mainstream gaming platform, dedicated enthusiasts still managed to programme impressive arcade clones and text adventures for the expanded systems.