A flippy disk (sometimes known as a "flippy") is a double-sided 5¼" floppy disk, specially modified so that the two sides can be used independently (but not simultaneously) in single-sided drives. Use of "flippy" disks was most common during the 8-bit home computer era of the early-to-mid 1980s.
Generally, there were two levels of modifications:
- For Disk Operating Systems that did not use the index hole in the disk to mark the beginnings of tracks, the "flippy" modification required only a new write-enable notch to be cut. For this purpose, specially designed single-square-hole hole punchers, commonly known as disk doublers, were produced and sold by third-party computer accessory manufacturers. Many users, however, made do with a standard (round) hole puncher and/or an ordinary pair of scissors for this job.
- For disk operating systems that did use index sync, a second index hole window had to be punched in both sides of the jacket, and for hard sectored formats, an additional window must be punched for the sector holes. While cutting a second notch was relatively safe, cutting additional windows into the jacket was at great peril to the disk within.
A number of floppy disk manufacturers produced ready-made "flippy" media. As the cost of media went down, and double-sided drives became the standard, "flippies" became obsolete.