Since the advent of the personal computer, ever-more compact data-storage systems have evolved. One of the most versatile is the magnetic disk.
Hard disks, also called hard drives, store the most data, and are generally found inside of computer units. Diskettes are 8.9 cm (3.5 in) across, and can be inserted and removed from recording/playback machines called diskette drives. In recent years, magnetic diskettes have been largely supplanted by nonmagnetic compact disc recordable (CD-R) and compact disc rewritable (CD-RW) media.
The principle of the magnetic disk, on the microscale, is the same as that of magnetic tape. The information is stored in binary digital form; that is, there are only two different ways that the particles are magnetized. This results in almost perfect, error-free storage. On a larger scale, the disk works differently than the tape because of the difference in geometry. On a tape, the information is spread out over a long span, and some bits of data are far away from others as measured along the medium itself. But on a disk, no two bits are ever farther apart than the diameter of the disk. This means that data can be stored to, and retrieved from, a disk much faster than is possible with tape.
The same precautions should be observed when handling and storing magnetic disks as are necessary with magnetic tape.