Magnetic storage is a method of storing information, both analogue and digital, which has been in popular use for decades. Examples of its use range from cassette tapes to computer hard disks.
A magnetic material, such as iron oxide or chromium oxide, is embedded in flexible tape or a disk. To record, a recording head moves past the tape or disk while electric currents passing through it produce a magnetic field. The magnetic field magnetises the material.
To read information, a reading head moves past the tape or disk. The magnetic fields from the magnetised material inside produce electrical currents in the head, which can then be interpreted to get the original information.
There are many examples of magnetic storage all around us. Cassette tapes are used to magnetically record and play audio. Video cassettes can do the same with video signals. Floppy disks use a magnetic disk to store digital information, and hard disks do the same at a much larger scale. Credit cards use a magnetic strip to hold their crucial information.