ZX Microdrive

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ZX Microdrive unit

Microdrive cartridge

Magazine advertisement for the ZX Microdrive and ZX Interface 1 bundle. The Microdrive unit is shown in the upper left tray of the retail box.

The ZX Microdrive was a tape-loop data storage system launched in July 1983 by Sinclair Research for the ZX Spectrum home computer. The Microdrive technology was later also used in the Sinclair QL and ICL One Per Desk personal computers. The primary engineer behind the Microdrive was Ben Cheese.

Typically of Sinclair Research, the ZX Microdrive was comparatively cheap (£49.95 at launch) and technologically innovative but also rather limited. Connection of a ZX Microdrive to a ZX Spectrum was done via the ZX Interface 1 unit, which was sold separately at £49.95 or bundled with at least one Microdrive for £29.95. Later, in March 1985, a Microdrive plus Interface 1 bundle called the ZX Spectrum Expansion System was sold for £99.95, and also included four cartridges with the Tasword Two word processing, Masterfile filing system, Games Designer and 3D Ant Attack game. A total of eight ZX Microdrive units could be connected to the computer by daisy chaining one drive to the next via flat-ribbon cables.

Microdrives used tiny (44 × 34 × 8 mm including protective cover) cartridges containing a 5 m (200 inch) endless loop of video tape, 1.9 mm wide, driven at 76 cm/second (30 in/second); 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/second (i.e., 120 kbit/s).

Unfortunately, the system acquired a reputation for unreliability, and the cartridges were relatively expensive (initially sold for £4.95 each, later reduced to £1.99). Similar technology was used in other devices, such as the Rotronics Wafadrive, and was sometimes known as a "stringy floppy".

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 that allowed each cartridge to hold at least 100 kB. The QL also included a Microdrive expansion bus allowing the attachment of up to six external QL Microdrives. These, however, were never produced, probably due to lack of demand.

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

[edit] External links

• ZX Microdrive information – At Planet Sinclair
• Sinclair User, April 1985, News section