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.


Background

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

Return to IDI home page
Historical notes.