The 3-inch floppy disk, or Compact Floppy, was designed by Hitachi along with other Japanese companies, and introduced in 1982.
3-inch floppies were double-sided in nature, and single-sided drive owners were able to flip the disk over to use the other side. The sides were termed “A” and “B” and were completely independent, with two write-protect switches. Each side of a double-density disk held 180 KB for a total of 360 KB per disk, and 720 KB for quad-density disks.
The 3-inch floppy has a more rigid casing than a 3½-inch floppy,and the metal shutter is opened by a sliding plastic tab.
Amstrad used the 3-inch floppy for their CPC and PCW ranges, 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 were also available for computers such as the TRS-80 and Apple II.
It suffered from a higher-price due to the elaborate and complex case mechanisms, and when Apple Computer chose to use the Sony 3½-inch drives in the Macintosh, that became the de facto standard for micro-floppy drives.
In 1991, Amstrad switched to 3½-inch floppies for the PCW range.