-up of a hard drive, showing platters and Read-Write Heads read-write head armature Platters Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Premises Technologies Premises Technologies Figure 5-5 Schematic diagram of a hard drive-As the platters spin, the read-write heads access the magnetized surfaces of each platter, writing information to and reading information from them. When the operating system formats a disk, it logically divides the disk into what are called cylinders, tracks, and sectors, as shown in Figure 5-6. It then uses those delimiters as a way to store and recall files on a drive, using three dimensions. When the operating system (OS) writes the file to the disk surface, there is every possibility (in fact it is likely) that the file will not be written to the surface in a contiguous stream of bits. Instead, the file may be broken into pieces, each of which may be written on a different part of the disk array. The pieces are linked together by the operating system using a series of pointers, which tell the os where to go to get the next piece of the file when the time comes to retrieve it. The pointer, of course, is a cylinder:track:sector indication. Cylinder Figure 5-6 Cylinders, tracks, and Track sectors on a typical disk Sector Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Premises Technologies Chapter 5 Cylinders, tracks, and sectors are relatively easy to understand. A track is a single writeable path on one platter of the disk array. A cylin- der is a "stack of tracks" on multiple platters. And a sector is a "pie slice" of the disk array. With a little imagination it is easy to see how a file can be stored or located on a disk by tracking those