Floppy disks are small, removable, media storage devices. They record data onto a thin, circular magnetic film encased in a flat, square plastic jacket. Floppy disks are somewhat antiquated, having been replaced by memory sticks and re-writable CD storage devices.

Original floppy disks were 8-inch floppies used in 1971-1975, but the first floppy disks that were widely used commercially were 5.25-inch disks. These floppy disks were quite flexible and required a 5.25-inch floppy drive. The disks could store up to 360 kilobytes (KB) of data, or about one third of a single megabyte. Later, high-density floppy disks held 1.2 megabytes (MB) of data. These floppy disks were widely used until about 1987.

As the technology of floppy disks improved, the next generation was smaller and eventually held more data. The newer 3.5-inch floppy disks also had hard shell cases for protection, making them less floppy. The term floppy disk was still used for many years, however. Some 3.5-inch floppy disks only utilized one side of the internal magnetic mylar film for recording data, with a capacity of 744 KB. High-density 3.5-inch floppy disks used both sides, doubling the capacity to 1.44 MB. In fact there were several configurations, including single or double sided (SS or DS), and single or double density (SD or DD).

An easy way to spot the lower capacity diskette was to look at the top corners of the case or jacket. If the diskette had only one hole, it was a single-sided diskette. Since single-sided floppy disks were cheaper than their higher-capacity high-density cousins, some people in the know would purchase the cheaper disks, then punch a hole in the opposite top corner to convert the disk to a double-sided high-density disk. All floppy disks contain mylar coated on both sides with the necessary magnetic film. Punching a second hole in the case allowed the floppy drive to spin the mylar in the opposite direction, thereby utilizing both sides of the film.

Today most 3.5-inch floppy disks are high-density and referred to simply as "diskettes." The term floppy disks is rarely used.

Various technologies have been used since 1991 in the attempt to extend the life of floppy disks by increasing capacity to 2.88 MB (extended density or ED), and even 120 MB and 240 MB (LS-120 and LS-240 respectively). However, none of these technologies caught on. The former proved to be too small an increase of capacity for ubiquitous adoption, and the latter an unreliable form of storage.

Today other storage devices that are more convenient and robust, such as compact disks and memory sticks, have largely replaced floppy disks. A CD can hold upwards up 600 MB, and even the smallest capacity memory stick holds several hundred times the amount of a single floppy disk. Some memory sticks now compete with smaller hard drives for disk capacity, making them ideal for transferring files, programs, or even entire volumes.

A real sign that floppy disks are all but obsolete is that most laptops no longer come with a floppy drive, and many desktop systems do not include a floppy drive unless requested. Nevertheless, many people continue to use diskettes for backing up and transferring small files.