Valdemar Poulsen, a Danish engineer, presents his Telegraphone, which can record sound magnetically onto a thin steel wire. Although wire recording was popular only for a few years in the late 1940s to early 1950s, before magnetic tape took over, it was the first manner of magnetic data storage and paved the way for the drums and hard disks of later computers.
Recording wires are made out of steel or stainless steel, and are only about as thick as a human hair. They are pulled past the recording head at a very high speed when compared to tape recorders, with the electrical signal of the sound supplied to the head and magnetising the wire as it passes. 
Playing back the wire without applying a signal to the head leads to the magnetic fields on the wire inducing the signal back into the head, the recorded sound can be reproduced. Despite the high speeds of recording and playback, the thinness of the wires allows for very high capacities. Wire recorders were thus sometimes able to record several hours of audio non-stop, in contrast to similarly-sized tape recorders.
The initially complex, heavy, and expensive magnetic tape recorders soon caught up to become a viable alternative for home use, and almost completely replaced wire recording during the 1950s. Magnetic tapes, first patented by Fritz Pfleumer in 1928, went on to become one of the main methods of data storage for home computers in the 1980s. But the principles first employed by Poulsen also lead to drum memories, floppy disks, and hard disk drives. Even in his 1898 patent, Poulson described that instead of a wire, one might use “a disk of magnetisable material over which the electromagnet may be conducted spirally,” or “a strip of some insulating material such as paper [covered] with a magnetisable metallic dust,” essentially predicting hard disks and magnetic strips as used on tickets or credit cards. Today, magnetic media continue to be the predominant forms of permanent computer data storage, to be rivalled only in certain applications by optical or semiconductor technologies.
Note: The Electrical World magazine issue of September 8, 1888, printed a description of magnetic recording by Oberlin Smith, who himself claimed to know about the principle from a visit to the Edison laboratories 10 years prior. However, it is not known whether any working model was ever built before Poulsen’s patented Telegraphone in 1898. In addition, Smith believed a continuous steel wire would not allow for precise magnetisation, and suggested regular wires furnished with steel dust.
« Return to Part I — Prehistory
References
- Wikipedia: Valdemar Poulsen, Wire recording, Fritz Pfleumer
- Magnetic recording history, University of San Diego (archived)
- 100 Years of Magnetic Recording, AMPS newsletter issue 27
- Picture: “Magnetone Magnetic Wire Recorder” by Radio Rover (CC 2.0 by-nc-nd)
