Offline Memory Technology
Part 3: Film And Magnetic Storage
By Baptiste Bouix
In 1839, Louis Daguerre created the daguerreotype, a method of capturing a picture on a polished metal sheet using chemicals. This is the beginning of photography, lit. “Writing with light”. In 1894, the Lumière brothers created the Cinématographe, a device able to write and read a photographic film – to create a movie and then project it with the same device. A real memory storage, all in one. Film became a major data storage medium.
One of the specificities of the photographic storage is to be able to use lenses to miniaturize the pictures. Therefore, a picture shown on a cinema screen is stored on a 35 millimeters-wide film. The microform photographic film (often called „microfilm“ in spy movies) is a way to store plans, texts, or photographs of original documents on a film, scaled down to 4% of their original size. Even the first computer codes were put on microfilm for distribution: the buyers had to project the film, and then type everything by hand.
Photographic storage is still used today: movie preservation is done with 35mm photographic film, and the IMAX 70mm film is a common movie distribution method. An IMAX projection has a resolution equivalent to 12000x8700 pixels, which would be roughly 120 gigabit per second of data. However, 90 minutes of movie projection (600 terabits of data) requires 22km of film. An IMAX film reel weights 200kg and sizes up to 1.8 meters diameter; a projector weights 2 tons and requires an industrial-scale power supply. This is not a viable data storage and transfer solution in most of the cases.
Photographic storage is interesting for its density of analog data, but it requires long and complexes chemical processes, and the output was not directly readable by a computer until the development of automated pattern recognitions techniques.
A 35 mm film reel containing the first few seconds of a movie
In parallel with photographic storage, advances in metallic compounds research allowed to deposit a layer of magnetic material on celluloid films. If you apply a large magnetic field to the material (generally with an electromagnet), you will change its magnetic orientation. This magnetic orientation can be measured using the same electromagnet. This allowed for writing and reading data with the same circuit. Initially used for analog data storage –especially audio and video, magnetic tape was also used for digital data storage, including magnetic cards in use for banking identification or as secure access keys.
A magnetic card used to access the Würth Elektronik France building's main entrance
Multiple format of magnetic tape existed, as manufacturers added cartridges and reels around the tapes. The Compact Cassette for music, the Betacam, DV or VHS for video and the quarter inch cartridges or Linear Tape-Open for data are such examples.
Multiple format of magnetic tape existed, as manufacturers added cartridges and reels around the tapes. The Compact Cassette for music, the Betacam, DV or VHS for video and the quarter inch cartridges or Linear Tape-Open for data are such examples.
A music cassette tape
Magnetic storage also exist in disk form: the now-legacy floppy disk. A disk coated with magnetic material, the floppy disk became available in the 1970’s, and became obsolete during the 2000’s.
A floppy disk (left) and a floppy disk reader (right)
Overall, it encompassed most pros and cons of magnetic tape storage: cheap, easy to use, more easily rewritable than optical disks, totally adapted to digital data and computer compatibility, but with low capacity.
Magnetic data storage still exists: hard disc drives are still not obsolete, even if their sales are now lower than solid-state drives. Comprised of many magnetic disks with a motor and a read/write head, they use the giant magnetoresistance effect to read and write the magnetic material with a much higher data density. Yet, with their mechanical moving parts, those disks are relatively large and fragile, not really adapted to mobile electronics – or anything smaller than a laptop, really. But they are still massively used in fixed applications where their lower access speed is not a problem.
Stay plugged!