History notes . . .

Data Storage Becomes Unimaginably
(and Unmanageably) Small and Inexpensive

by Conrad Weisert, April 2, 2017
©Information Disciplines, Inc.

NOTE: This document may be circulated or quoted from freely, as long as the copyright credit is included.


Just three years ago we paid a nostalgic tribute to the IBM 2314, a direct-access storage device introduced in 1965. By comparison with its predecessors it was amazingly small taking up a reasonable quantity of floorspace and supporting removable media that a human operator could easily carry. In that article we also noted the current growing availability of much smaller high-capacity devices.

Progress in storage technology continues. A recent ComputerWorld article (part 1 of 2) surveys the amazing growth in capacity, reduction in physical size, and lowering of per-byte cost in storage technology.

Management Issues

The storage subsystems of 1960s and 1970s large-scale operating systems supported global cataloguing.1 When a program created a new data-set2 the operating system would make an entry in its catalog, associating the data-set name with its physical location. Subsequent retrieval of the data-set was by name only, specified through the Job-Control Language. Neither the jobs themselves nor the users who submitted them needed to know where the desired data set was stored.

The data-set location, recorded in the catalog, could be either on a permanently mounted device or on an off-line volume, which the operator would be instructed to fetch and mount. That scheme worked not only for disks and other direct-access devices but also for old-fashioned tape reels.3

The catalog, of course, had to be permanently mounted so that the operating system could access it quickly. Unfortunately, maintaining a global catalog of every data-set in an organization became unwieldy as:

  1. the number of data-sets grew beyond 1970s expectations.
  2. the storage volumes became increasingly portable, fitting in pockets and briefcases.
A major computer center today can no-longer depend upon a global catalog or even upon easily stored and retrieved physical volumes. We shall explore these serious management and housekeeping issues in a later article.
1—An optional feature of OS/360 and its successors, almost always exploited by well-managed computer centers.
2—"Data set" was IBM terminology for what others call a "file".
3—Except for interfaces with foreign devices, tapes were expected to begin with a standard label record that included a permanent reel number. A paste-on sticker displayed the same serial number on the outside of the reel, and no information about the content needed to be visible.

Last modified April 2, 2017

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Historical notes.