The ZX Microdrive is a magnetic-tape data storage system launched in July 1983 by Sinclair Research for its ZX Spectrum home computer. It was proposed as a faster-loading alternative to the cassette and cheaper than a floppy disk, but it suffered from poor reliability and lower speed. Microdrives used tiny cartridges containing a endless loop of magnetic tape, 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 personal computers. Development 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 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, and never worked for Sinclair Research. Development of the ZX Microdrive hardware by Sinclair engineers Jim Westwood, David Southward and Ben Cheese started in 1982. Products 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), Masterfile (a database), Quicksilva's Games Designer and Ant Attack games, and an introductory cartridge. Technology Microdrives used tiny ( including protective cover) cartridges containing a endless loop of magnetic tape, 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