ZX Microdrive unit The ZX Microdrive is a

magnetic-tape data storage Magnetic-tape data storage is a system for storing digital information on magnetic tape using digital recording. Tape was an important medium for primary data storage in early computers, typically using large open reels of 7-track, later ...

system launched in July 1983 by

Sinclair Research Sinclair Research Ltd is a British consumer electronics company founded by Clive Sinclair in Cambridge in the 1970s. In 1980, the company entered the home computer market with the ZX80 at £99.95, at that time the cheapest personal computer ...

for its

ZX Spectrum The ZX Spectrum () is an 8-bit computing, 8-bit home computer developed and marketed by Sinclair Research. One of the most influential computers ever made and one of the all-time bestselling British computers, over five million units were sold. ...

home computer Home computers were a class of microcomputers that entered the market in 1977 and became common during the 1980s. They were marketed to consumers as affordable and accessible computers that, for the first time, were intended for the use of a s ...

. 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, a diskette, or a disk) is a 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 with a ...

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

endless loop In computer programming, an infinite loop (or endless loop) is a sequence of instructions that, as written, will continue endlessly, unless an external intervention occurs, such as turning off power via a switch or pulling a plug. It may be inte ...

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 magnetic ...

, 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 The Sinclair QL (for ''Quantum Leap'') is a personal computer launched by Sinclair Research in 1984, as an upper-end counterpart to the ZX Spectrum. The QL was the last desktop microcomputer from Sinclair Research aimed at the serious home use ...

and ICL One Per Desk

personal computer A personal computer, commonly referred to as PC or computer, is a computer designed for individual use. It is typically used for tasks such as Word processor, word processing, web browser, internet browsing, email, multimedia playback, and PC ...

Development

It is claimed the Microdrive concept was originally suggested by Andrew Grillet at an interview with Sinclair Research in 1974. Grillet was offered a better-paying job at

Xerox Xerox Holdings Corporation (, ) is an American corporation that sells print and electronic document, digital document products and services in more than 160 countries. Xerox was the pioneer of the photocopier market, beginning with the introduc ...

, 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. Sir ...

, 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 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 word ...

), ''Masterfile'' (a

database In computing, a database is an organized collection of data or a type of data store based on the use of a database management system (DBMS), the software that interacts with end users, applications, and the database itself to capture and a ...

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

's ''Games Designer'' and ''

Ant Attack ''Ant Attack'' is an action game written for the ZX Spectrum by Sandy White and published by Quicksilva in 1983. A Commodore 64 version was released in 1984. While ''Zaxxon'' and ''Q*bert'' previously used isometric projection, ''Ant Attack'' ad ...

'' games, and an introductory cartridge.

Technology

Microdrives use tiny ( including protective cover) cartridges containing a

, wide, driven at 76 cm/ s (30 in/s); thus performing a complete circuit in approximately 8 seconds. The cartridges hold a minimum of 85 KB when formatted on a ZX Microdrive (exact capacity depended on the number of

bad sector Bad Sector is an ambient/noise project formed in 1992 in Tuscany, Italy by Massimo Magrini. While working at the Computer Art Lab of ISTI in Pisa (one of the CNR institutes), he developed original gesture interfaces that he uses in live pe ...

s found and the precise speed of the Microdrive motor when formatting). The data retrieval rate is 15 KB/s, i.e., 120

kbit/s In telecommunications, data transfer rate is the average number of bits ( bitrate), characters or symbols ( baudrate), or data blocks per unit time passing through a communication link in a data-transmission system. Common data rate units are mu ...

. It is possible to "expand" the capacity of a fresh microdrive cartridge by formatting it several times. This causes 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. The operating system automatically marks bad sectors during formatting, so storage capacity decreases over time. A total of eight ZX Microdrive units can 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. with tapes experiencing excessive wear because of friction. Sinclair stated that improved manufacturing fixed the problem, but ''BYTE'' reported that two of 11 QL tapes failed during testing. The tapes stretch during use (giving them a short life span), eventually rendering the data stored unreadable. The "write protection" is software-based; a computer crash can 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 are also the native storage medium of the Sinclair QL, which incorporate two internal drives. These are very similar to the ZX Microdrive, but use a different logical format, allowing each cartridge to hold at least 100 KB. Mechanically the drives are similar, but run slightly slower and have 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 is 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 One Per Desk system (also badged as the

Merlin Tonto The One Per Desk, or OPD, was a British innovative hybrid personal computer and 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 United ...

and Telecom Australia Computerphone). These drives were re-engineered by ICL for greater reliability, and use a format incompatible with both ZX and QL Microdrives.

References

External links