Acorn double density 3 1/2" disk

The Acorn double density 3 1/2" 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 succeeded the Acorn double density 5 1/4" disk, and was succeeded by the Acorn high density 3 1/2" disk.

The disks were double sided, with 80 tracks per side and variants having 16 sectors of 256 bytes, and 5 sectors of 1024 bytes, for a total capacity of 640 or 800 kilobytes respectively. MFM encoding was used.

The ADFS (Advanced Disc Filing System) was used as the file system, and BBC BASIC tokenized files were among the file types stored.