Microdrive

One-inch disks typically held about 8 to 10 GB and microdrives were either 2 or 4 GB.

1984, Alison Maguire, interviewed in SINCLAIR talks... (in Crash magazine, issue 3, April 1984) http://www.crashonline.org.uk/03/sinclair.htm There are lots of things that will benefit from being on a microdrive cartridge but if you release something on microdrive you're only going to sell it to people with microdrive.

The Spectrum has its own inexpensive mass storage unit - the microdrive which starts at about £150 for 100k of storage, but this may not be suitable in all cases, since the storage unit may be damaged if turned on with the disc in position.

Disk interfaces have been around since the year dot, as people soon realised that the microdrive was unreliable, unstable and generally rubbish for the storage of anything, useless except as a rather small beermat.

The microdrive was invented so that electrodes could be lowered into the brain in order to isolate new neurons.