The 3-inch floppy disk (also known as the Compact Floppy or CF2) was designed by Hitachi, Matsushita and Maxell, and introduced in 1982.
3-inch floppy disks were double-sided in nature, and needed to be turned over in single-sided drives to use the other side. To distinguish the two sides, they were labelled ‘A’ and ‘B’ and the disk had independent write-protect switches. Each side of the disk held 180 KB for a total of 360 KB per disk, or 720 KB for double-density (CF2-DD) disks.
The 3-inch floppy has a more rigid casing than a 3.5-inch microfloppy, and the metal shutter is opened by a sliding plastic tab. The disks are just over 3-inches wide, and nearly 4-inches long.
The main user of the 3-inch disk format was the UK-based Amstrad company, that used the 3-inch floppy for their CPC and PCW ranges from 1985 and later used it for the Sinclair ZX Spectrum +3. It was also used for the Oric-1 and Oric Atmos, Tatung Einstein, and some MSX systems, as well as some more obscure computers. External drives produced by AmDisk were also available for computers such as the TRS-80 and Apple II.
The disks were expensive due to the complex case design. The rival 3.5-inch microfloppy disk was chosen by Apple for use in the Macintosh in 1984, and in 1987 IBM used it in the PS/2 range (in it’s high-density version) making it the standard for floppy disk drives.
In 1991, Amstrad switched to the 3.5-inch high-density microfloppy for the PCW range.