Computer Science

Computing History Displays: Fifth Floor - Magnetic Data Storage

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The most common forms of permanent data storage used in modern computers - hard disks and archival tapes - represent data as magnetized "bars" on the surface of a thin medium, where writing and reading of data requires mechanical movement of the medium. This type of data storage was used in the very first computers at the end of the 1940s. In the succeeding 60 years the technology has been improved to an extent that is just as remarkable as improvements to computer electronic circuitry over the same period.

Just how much progress has been made? One of the first computers to use a magnetic storage was the ERA Atlas of 1950. It stored 16384 24-bit words on a drum 8.5 inches diameter and 14 inches length - this is a density of about 400 bits/ per cubic inch (because disk storage was initially a United States endevour, non-metric units are most commonly used when talking about magnetic storage.) Contrast the Toshiba MK 1031GAS in 2005 which stores 100 GBytes in 4 cubic inches for a density of over 200 billion bits per cubic inch. The improvement in density of storage is about 0.5 billion, but the Atlas drum needed additionally a motor, power supply and controller, whereas the Toshiba is self-contained, so we can claim that the improvement in density is a billion in round numbers. There are other ways of measuring improvement, such as bits per dollar, but consideration of these also put the progress as over a billion-fold! (And now, in 2009, disks of 2 TByte are available, so the progress continues!)

Magnetic data storage is such a big topic that we have split its description into a number of sections:


For this display detailed information has been derived from a number of references:

  • Magnetic recording - The First Hundred Years
    Eds Eric D. Daniel, C. Denis Mee, Mark H. Clark
    IEEE Press 1999

  • Magnetic Disk Drive Technology
    Heads, Media, Channel, Interfaces and Integration
    Kanu G Ashar
    IEEE Press 1997

  • Magnetic Field Nanosensors
    Stuart A. Solin
    Scientific American, July 2004, pp 45-51.

  • Quantum DLT tape (TM) handbook.

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