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