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:

    “I make this direct statement to the American people that there is far less chance of the United States getting into war, if we do all we can now to support the nations defending themselves against attack by the Axis than if we acquiesce in their defeat, submit tamely to an Axis victory, and wait our turn to be the object of attack in another war later on.”
    —Franklin D. Roosevelt (1882–1945)

    “Make thick my blood,
    Stop up th’ access and passage to remorse,
    That no compunctious visitings of nature
    Shake my fell purpose.”
    —William Shakespeare (1564–1616)

    “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)