Double-sided disk

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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 the double-sided disk, which offered double the capacity in the same physical size. Initially, double-sided disks had to be removed and flipped over to access data on the other side, but eventually devices were made that could read both sides without the need to eject the disk.

A commercially-made floppy disk "notcher"

Manufacturers sold both single-sided and double-sided disks with the double-sided disks being typically 50% more expensive than single-sided disks. While the magnetic-coated medium was coated on both sides, the single-sided floppies had a read-write notch on only one side, thus allowing only one side of the disk to be used. When users discovered this, they began buying the less-expensive single-sided disks and "notching" them using scissors, a hole punch, or a specially-designed "notcher" to allow them to write to the reverse side of the disk.

DVDs also are available in single-sided and double-sided formats. When used for movie releases, double-sided DVDs typically have the widescreen (or letterbox) version of the movie on one side, and the pan and scan (sometimes called "fullscreen") version on the opposite side. Some releases place the feature on one side, and the "extras" on the opposite. It is more common, however, for movies to be released on single-sided, dual-layer discs, with the film and extras on the same side, and widescreen and letterbox versions packaged separately. Some particularly lengthy films like Schindler's List and Oliver! are divided between the two sides, starting on Side A and continuing on Side B, and include a prompt for when to flip the disc (identically to a LaserDisc).

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