The method by which binary data is recorded on magnetic media. In horizontal recording on magnetic disks, tapes, and cards, magnetic domains in the media are aligned along the direction of the applied magnetic field with either north or south pole leading: each domain is a tiny bounded region in which the magnetic moments of the component atoms are aligned, and it therefore behaves like a magnet. The domains are arranged end to end along a track, which may be either a concentric ring on a disk or run the length of a tape or card. There may not be a one-to-one relationship between the binary information of the data and the orientation of the magnetic domains. See also disk format, tape format.

In 1975 Shun-ichi Iwasaki published his work on vertical recording methods. The magnetic domains are oriented through the thickness of the magnetic film and have either a north or a south pole at the exposed surface. The magnetic material is usually a vacuum-deposited film of metal such as an alloy or combination of cobalt and chromium over a layer of permalloy. Vertical recording can yield an increase of at least 25 times and possibly 100 times the bit density achievable by current horizontal recording techniques. However, vertical recording proved difficult to implement. Disks using it began to appear in the 2000s.