1. (of a storage subsystem) The logic assembly that determines the format of data recorded on magnetic or optical media, and forms part of a device controller. See also disk format, tape format.

2. (text formatter) A program that accepts text with embedded formatting instructions and produces a new version of the document with the specified margins, justification, pagination, etc.

3. A program that checks the surface of a magnetic disk or tape by writing and then reading a set pattern to every point on the medium. Any unusable or damaged portions will be marked as such to avoid their use for data storage; alternative portions may be assigned in their place. New media must be formatted before use; the re-formatting of used media has the effect of totally erasing all the data stored thereon, although specialized recovery techniques can sometimes save information after accidental re-formatting.