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 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 an ordinary pair of scissors for this job.
For OSes 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.
=Special cases=
At least one manufacturer created a diskette drive for the TRS-80 platform with two index read sensors so that the disk could be flipped over without the necessary index hole punch. Data written with these rare drives complicates conversions today for retrocomputing archivists due to the sector offset skewing: the sectors start earlier than they would using the standard index hole placement.