Direct Access Storage Device

Direct Access Storage Device

In mainframe computers and some minicomputers, a direct access storage device, or DASD ( /ˈdæzdiː/), is any secondary storage device which has relatively low access time relative to its capacity.

Historically, IBM introduced the term to cover three different device types:

  1. disk drives
  2. magnetic drums
  3. data cells

The direct access capability, occasionally and incorrectly called random access (although that term survives when referring to memory or RAM), of those devices stood in contrast to sequential access used in tape drives. The latter required a proportionally long time to access a distant point in a medium. Note: The storage CLASS of DASD is both Fixed and Removable. The access methods for DASD are Sequential, Indexed and Direct.

Read more about Direct Access Storage Device:  Architecture, Access, Present Terminology

Famous quotes containing the words direct, access, storage and/or device:

    Traditionally in American society, men have been trained for both competition and teamwork through sports, while women have been reared to merge their welfare with that of the family, with fewer opportunities for either independence or other team identifications, and fewer challenges to direct competition. In effect, women have been circumscribed within that unit where the benefit of one is most easily believed to be the benefit of all.
    Mary Catherine Bateson (b. 1939)

    The Hacker Ethic: Access to computers—and anything which might teach you something about the way the world works—should be unlimited and total.
    Always yield to the Hands-On Imperative!
    All information should be free.
    Mistrust authority—promote decentralization.
    Hackers should be judged by their hacking, not bogus criteria such as degrees, age, race, or position.
    You can create art and beauty on a computer.
    Computers can change your life for the better.
    Steven Levy, U.S. writer. Hackers, ch. 2, “The Hacker Ethic,” pp. 27-33, Anchor Press, Doubleday (1984)

    Many of our houses, both public and private, with their almost innumerable apartments, their huge halls and their cellars for the storage of wines and other munitions of peace, appear to me extravagantly large for their inhabitants. They are so vast and magnificent that the latter seem to be only vermin which infest them.
    Henry David Thoreau (1817–1862)

    It is my hope to be able to prove that television is the greatest step forward we have yet made in the preservation of humanity. It will make of this Earth the paradise we have all envisioned, but have never seen.
    —Joseph O’Donnell. Clifford Sanforth. Professor James Houghland, Murder by Television, just before he demonstrates his new television device (1935)