Appendix B. Appendix: Disk Drive History

Table of Contents

B.1. Disk Drive Components
B.2. Access Modes
B.2.1. CHS Addressing
B.2.2. LBA Addressing
B.3. The Master Boot Record

Disk drives, and how they are accessed, is a broad subject which has changed greatly over time. Some facts are actually just misconceptions which are taken as canon. This section will attempt to sort the facts from fiction and give some sort of historical account of how the software and hardware has changed over time.

B.1. Disk Drive Components

In the early days of computing, direct access storage devices (i.e., hard disk drives) were much simpler. A simple device meant a less complex method for interaction was necessary. Two standards define how communication with disk drives may happen: The IDE/ATA standard for communicating with disk drives, and the BIOS Int 13h standard (disk services) for how operating systems can interact with disk drives via software interrupts [51] [52] .

A disk drive was originally composed of a few simple components:

  • One called a head which is mounted on a swinging arm. The arm swings across a disk platter to move the head to the sector requested for a read or write operation. More platters in a disk drive mean more heads and arms.

  • An array of magnetized spinning disks called platters. Because each side of a platter is used to store data there must be two heads for each platter.

  • For the purpose of addressing a specific location on a platter each platter is further broken down into cylinders (or tracks), and sectors.

Figure B.1. Disk Drive Components

Disk Drive Components

[51] BIOS Enhanced Disk Drive Specification v3: