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O 1997

Last updated
26 Feb 1998

Technoturkeys: The Sinclair Microdrive

DAILY TELEGRAPH, 28 October 1997


BY February 1983 Sir Clive Sinclair had sold a million ZX80, 81 and Spectrum computers. They all used an ordinary audio cassette for storage which was painfully slow. Sinclair promised a secret alternative, which would speed access dramatically, while costing less than a floppy drive. The new Quantum Leap or QL computer would use the same device, when launched the next January.

When the mystery Microdrive was unveiled in July 1983, it turned out to be a much miniaturised version of the eight-track audio cartridge. A loop of 1.9mm tape, half the width of audio cassette tape, ran at 76cms a second, twice the speed used for studio recordings.

The tape was 23 microns thick and the loop was six metres long. At the end of each full run the heads stepped sideways to read new tracks. This made it faster to search for data. Each cartridge stored 100 kilobytes of data, which streamed at 15 kb a second.

Thorn-EMI's DataTech made the drives, BASF supplied the tape and Ablex in Bridgnorth built a machine with large spools to mass-duplicate programs.

Although the drive cost only 50, it needed a 50 interface to connect to the Spectrum. Blank cartridges cost 5. Even so, initial demand was so heavy that Sinclair rationed two drives for every registered Spectrum owner.

The Microdrive was a remarkable feat of engineering, but the flimsy tape was prone to tangling and there were problems of compatibility between tapes recorded on different drives. By January 1985, cartridge cost was cut to 2. Ablex offered free duplication to try to stimulate QL sales. But the QL flopped and the price of disk drives fell.