ZX Microdrive unit The ZX Microdrive is a magnetic-tape data storage system launched in July 1983 by Sinclair Research for its

ZX Spectrum The ZX Spectrum () is an 8-bit home computer that was developed by Sinclair Research. It was released in the United Kingdom on 23 April 1982, and became Britain's best-selling microcomputer. Referred to during development as the ''ZX81 Colou ...

home computer. It was proposed as a faster-loading alternative to the cassette and cheaper than a

floppy disk A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined ...

, but it suffered from poor reliability and lower speed. Microdrives used tiny cartridges containing a endless loop of

magnetic tape Magnetic tape is a medium for magnetic storage made of a thin, magnetizable coating on a long, narrow strip of plastic film. It was developed in Germany in 1928, based on the earlier magnetic wire recording from Denmark. Devices that use magnet ...

, which held a minimum of 85 kB and performed a complete circuit in approximately eight seconds. The Microdrive technology was later also used in the Sinclair QL and ICL

One Per Desk The One Per Desk, or OPD, was an innovative hybrid personal computer/telecommunications terminal based on the hardware of the Sinclair QL. The One Per Desk was built by International Computers Limited (ICL) and launched in the UK in 1984. It wa ...

personal computer A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or te ...

Development

Microdrive cartridge with case It is claimed the Microdrive concept was originally suggested by Andrew Grillet at an interview with Sinclair Research in 1974. Grillet proposed "a version of the Learjet

Stereo 8 The 8-track tape (formally Stereo 8; commonly called eight-track cartridge, eight-track tape, and eight-track) is a magnetic tape sound recording technology that was popular from the mid-1960s to the early 1980s, when the compact cassette, wh ...

system, modified to allow two 64k core images per track for roll-out roll-in swapping using the KUTS protocol". Grillet was offered a better-paying job at

Xerox Xerox Holdings Corporation (; also known simply as Xerox) is an American corporation that sells print and digital document products and services in more than 160 countries. Xerox is headquartered in Norwalk, Connecticut (having moved from St ...

, and never worked for Sinclair Research. Development of the ZX Microdrive hardware by Sinclair engineers

Jim Westwood Jim Westwood is the former chief engineer who worked at Sinclair Research Ltd in the 1980s, starting at the company in 1963. Westwood was the technical mastermind behind many of Sinclair's products and worked there for more than twenty years. Si ...

, David Southward and Ben Cheese started in 1982.

Products

Opened microdrive cartridge, with a cassette tape for comparison The Microdrive was comparatively cheap (£49.95 at launch) and technologically innovative but also rather limited. Connecting a ZX Microdrive to a ZX Spectrum required the

ZX Interface 1 ZX may refer to: Arts and entertainment * Kamen Rider ZX (pronounced "Zed-Cross"), the tenth fictional superhero in the "Kamen Rider" franchise * ''Mega Man ZX'', a video game for the Nintendo DS * ''ZX Tunes'', remastered soundtracks of the "Meg ...

unit, costing £49.95, although this could be bought packaged with a Microdrive for £79.95. Later, in March 1985, the ''ZX Spectrum Expansion System'' was launched for £99.95. This consisted of Interface 1, a Microdrive, a blank cartridge and several cartridges containing '' Tasword Two'' (a

word processor A word processor (WP) is a device or computer program that provides for input, editing, formatting, and output of text, often with some additional features. Early word processors were stand-alone devices dedicated to the function, but current ...

), ''Masterfile'' (a

database In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases ...

Quicksilva Quicksilva was a British games software publisher active during the early 1980s. Quicksilva was founded by Nick Lambert in 1979. The name Quicksilva was inspired by a particular guitar solo in a track on the album Happy Trails by Quicksilver Mess ...

's ''Games Designer'' and ''

Ant Attack ''Ant Attack'' is a ZX Spectrum computer game by Sandy White, published by Quicksilva in 1983. It was converted to the Commodore 64 in 1984. While ''Zaxxon'' and '' Q*bert'' previously used isometric projection, ''Ant Attack'' added an extra d ...

'' games, and an introductory cartridge.

Technology

Microdrives used tiny ( including protective cover) cartridges containing a endless loop of

, wide, driven at 76 cm/ s (30 in/s); thus performing a complete circuit in approximately 8 seconds. The cartridges held a minimum of 85 kB when formatted on a ZX Microdrive (exact capacity depended on the number of "bad" sectors found and the precise speed of the Microdrive motor when formatting). The data retrieval rate was 15 kB/s, i.e., 120 kbit/s. It was possible to "expand" the capacity of a fresh microdrive cartridge by formatting it several times. This caused the tape to stretch slightly, increasing the length of the tape loop, so that more sectors can be marked out on it. This procedure was widely documented in the Sinclair community magazines of the 1980s. A total of eight ZX Microdrive units could be connected to the Interface 1 by daisy chaining one drive to the next via an electrical connector block. The system acquired a reputation for unreliability."Microdrive — 1983"
Planet Sinclair. The tapes stretched during use (giving them a short life span), eventually rendering the data stored unreadable. Also the "write protection" was software-based, thus a computer crash could erase the data on an entire tape in 8 seconds. The cartridges were relatively expensive (initially sold for £4.95 each, later reduced to £1.99).

Later uses

The Sinclair QL featured dual internal Microdrives Microdrives were also used as the native storage medium of the Sinclair QL, which incorporated two internal drives. These were very similar to the ZX Microdrive, but used a different logical format, allowing each cartridge to hold at least 100 kB. Mechanically the drives were similar, however, they ran slightly slower and had a take-up acceleration start instead of the instant start of the ZX Spectrum drives, putting less strain on the cartridges. The QL also included a Microdrive expansion bus, allowing the attachment of up to six external QL Microdrives. These were never produced, probably due to lack of demand. It was, however, possible to connect ZX Microdrives to a QL by putting a twist in the cable. In addition to the QL versions, dual internal Microdrives were included in the related ICL

system (also badged as the Merlin Tonto and Telecom Australia Computerphone). These drives were re-engineered by ICL for greater reliability, and used a format incompatible with both ZX and QL Microdrives.

References

External links