Acorn single density 5 1/4" disk
The Acorn single density 5 1/4" disk was used with Acorn computers, a line of computers from the UK in the 1970s through 1990s, which included the popular BBC microcomputer, and eventually led to RISC OS. It was succeeded by the Acorn double density 5 1/4" disk, the Acorn double density 3 1/2" disk, and the Acorn high density 3 1/2" disk.
The disks had two variants, with 40 and 80 tracks, each with 10 sectors to the track and 256 bytes per sector, for a capacity of 100 and 200 kilobytes respectively. They were single-sided disks. FM encoding was used.