QL Microdrive
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, allowing each cartridge to hold at least 100 kB. Mechanically the drives were similar however they ran slightly slower, and had a take-up acceleration start instead of the instant start of the ZX Spectrum drives, putting less strain on the cartridges. The QL also included a Microdrive expansion bus allowing the attachment of up to six external QL Microdrives. These were never produced, probably due to lack of demand. It was however possible to connect ZX Microdrives to a QL by putting a twist in the cable.
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, and used a format incompatible with both ZX and QL Microdrives.
Read more about this topic: ZX Microdrive