A flippy disk is a double-sided

Double-sided disk

In computer science, a double-sided disk is a disk of which both sides are used to store data.Early floppy disks only used one surface for recording. The term "single sided disk" was not common until the introduction of double-sided disks, which offered double the capacity in the same physical size...

 5¼" floppy disk

Floppy disk

A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...

, 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

8-bit

The first widely adopted 8-bit microprocessor was the Intel 8080, being used in many hobbyist computers of the late 1970s and early 1980s, often running the CP/M operating system. The Zilog Z80 and the Motorola 6800 were also used in similar computers...

 home computer

Home computer

Home computers were a class of microcomputers entering the market in 1977, and becoming increasingly common during the 1980s. They were marketed to consumers as affordable and accessible computers that, for the first time, were intended for the use of a single nontechnical user...

 era of the early-to-mid 1980s.

Generally, there were two levels of modifications:

• For Disk Operating System
  Disk operating system
  Disk Operating System and disk operating system , most often abbreviated as DOS, refers to an operating system software used in most computers that provides the abstraction and management of secondary storage devices and the information on them...
  
  s that did not use the index hole
  Hard sectoring
  Hard sectoring in a magnetic or optical data storage device is a form of sectoring which uses a physical mark or hole in the recording medium to reference sector locations....
  
   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.

Special cases

• At least one manufacturer created a diskette drive for the TRS-80
  TRS-80
  TRS-80 was Tandy Corporation's desktop microcomputer model line, sold through Tandy's Radio Shack stores in the late 1970s and early 1980s. The first units, ordered unseen, were delivered in November 1977, and rolled out to the stores the third week of December. The line won popularity with...
  
   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
  Retrocomputing
  Retrocomputing is the use of early computer hardware and software today. Retrocomputing is usually classed as a hobby and recreation rather than a practical application of technology; enthusiasts often collect rare and valuable hardware and software for sentimental reasons...
  
   archivists due to the sector offset skewing: the sectors start earlier than they would using the standard index hole placement.

Two versions on one disk

• During the time of single sided floppy disks some software manufacturers would use the two sides of one floppy disk to store two different copies of the same program. Each side would contain one copy of the program designed to be run on a different computer architecture. For instance several games were released that contained a Commodore 64
  Commodore 64
  The Commodore 64 is an 8-bit home computer introduced by Commodore International in January 1982.Volume production started in the spring of 1982, with machines being released on to the market in August at a price of US$595...
  
   version on one side and an Apple II or an Atari 8-bit
  Atari 8-bit family
  The Atari 8-bit family is a series of 8-bit home computers manufactured from 1979 to 1992. All are based on the MOS Technology 6502 CPU and were the first home computers designed with custom coprocessor chips...
  
   version on the other side of the disk. These releases were short lived however. When double sided floppy drives became common on gaming platforms this technique soon disappeared.

• As an easter egg
  Easter egg (media)
  Image:Carl Oswald Rostosky - Zwei Kaninchen und ein Igel 1861.jpg|250px|thumb|right|Example of Easter egg hidden within imagerect 467 383 539 434 desc none...
  
  , the Apple II version of Karateka, a 1984 computer game by Jordan Mechner
  Jordan Mechner
  Jordan Mechner is an American video game designer, screenwriter, author, and filmmaker, best known for creating the Prince of Persia video game franchise.- Life and career :Mechner was born in New York City...
  
  , contained a second version placed on the flip side of the disk. If one put the disk into the drive upside-down, the game played identically to the first side, except that the game was displayed vertically flipped.