---
title: "Disk Operating Systems"
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slug: "disk-operating-systems"
url: "http://localhost/article/disk-operating-systems/"
markdown_url: "http://localhost/article/disk-operating-systems.md"
published_at: "2026-11-09T22:33:06+00:00"
modified_at: "2026-11-09T22:33:06+00:00"
featured_image:
  url: "http://localhost/wp-content/uploads/2022/04/20230809-041332.jpg"
excerpt: "Historically, computer disks augmented or replaced magnetic tape reels. Essentially, a tape was pasted into a loop and flattened. The loop was fastened to a disk and spun under the usual read head. Because so many tracks could be accommodated, a movable head replaced multiple heads. In the interests of efficiency, several disks were stacked…"
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indiv:
  - name: "William J. Pedersen"
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publication: "Update Magazine"
publication_r:
  id: 10283
  title: "Update Magazine"
  type: "periodical"
  url: "http://localhost/periodical/update-magazine/"
authors: "Bill Pedersen"
issues_articles:
  - id: 26487
    title: "Update April 1992"
    type: "issue"
    url: "http://localhost/issue/ts-2068-up-date-april-1992/"
pages: "10"
pubdate: "April 1992"
archive_link: false
volumeissue: "vn"
---

# Disk Operating Systems

Historically, computer disks augmented or replaced magnetic tape reels. Essentially, a tape was pasted into a loop and flattened. The loop was fastened to a disk and spun under the usual read head. Because so many tracks could be accommodated, a movable head replaced multiple heads. In the interests of efficiency, several disks were stacked in a single drive. Early “stacks” which were removable did not use the top and bottom surfaces. Head loading was the opposite of the familiar caliper method and heads retracted.

The addressing method for stack drives is universal. The terms volume, head, cylinder, track, and sector are all derived from them, though there is some ambiguity in interpretation at times. There were also drives in the form of a cylinder with many, many heads for fast mainframe computers.

**VOLUME** This generally refers to a lump of storage you can carry around. When the lump is handled by a jukebox type machine it is considered the same as removable storage except for label checking. It doesn’t imply any particular medium of storage or an address. It could even be a book given modern character recognition technology.

**CYLINDER** A track on one side of one disk lines up with corresponding ones on every other disk and available side. Together they define a cylinder. Cylinders are numbered from the outside edge inward. This is NOT the track number. See why in a moment.

**HEAD** This is either specified or included implicitly in SIDE. Usually, but not always, heads are numbered from bottom to top. A removable stack of 7 disks would have six pairs of sensitive surfaces and six pairs of heads. Heads would be numbered 0 through 11. For a 2 disk caliper stack (small hard drive), they number from 0 through 3.

**“SIDE”** When there is only one disk in the stack, it is common to refer to SIDE instead of HEAD. This can be confusing if you forget they are different things entirely.

**“TRACK”** With a single sided disk TRACK is the same as CYLINDER. Adding a second side introduces ambiguity. If you use TRACK and SIDE together, TRACK and CYLINDER **NUMBERS** match, BUT…

Some disk systems treat even TRACK numbers to be on SIDE 0 and odd numbers to be on SIDE 1. Oh boy! Let’s stick with **DEVICE** (DRIVE), **VOLUME**, **HEAD**, **CYLINDER** and **SECTOR** and save us some headaches.

If we talk about TRACK as a physical storage unit, there is no problem. It is a very useful term, meaning a continuous place to record with no breaks, only ends. Any numbering of tracks is arbitrary.

[![Diagram of a disk stack showing the cylinder, heads 0-9 and a disk face divided into sectors 0-9](http://localhost/wp-content/uploads/2026/11/update-new-disk-operating-systems-1-1024x711.png)](http://localhost/wp-content/uploads/2026/11/update-new-disk-operating-systems-1.png)Diagram of a disk stack showing the cylinder, heads 0-9 and a disk face divided into sectors 0-9