Mitsumi Quick Disk
Company: Mitsumi
Launched: 1985
Capacity: 100 Kib ~ 256 Kib
The Quick Disk (QD) was a 3-inch floppy disk design released by Mitsumi around 1985 (although a prototype was shown in 1984).
It was encased in plastic, but had a much simpler design than other floppy disks of the time, as it lacked a shutter mechanism to protect the disk surface from dust and used removable tabs (rather than a sliding tab) for write protection on each side.
Furthermore, instead of offering random access, data was recorded in a continuous spiral on the disk (like vinyl) that took about 8 seconds to read (on the 100 KB Triton QD drive), making it very slow (this sequential access made it similar to a tape and prevented the fast access benefits of a floppy disk).
The drives were single-sided, and the disks had to be manually removed and rotated to use the other side.
It was used by some home computers in the mid-1980s, such as the Sinclair ZX Spectrum, Dragon 32/64, Sharp MZ-700 and MZ-800, Commodore 64, some MSX computers, and was most prevalent in Thompson computers.
Capacity ranged from 100 KB to 256 KB.
