pyright © 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 identical to what is found on recording tape. Adjacent to the platters, which are mounted on a spindle attached to a high-speed motor, is an armature upon which is mounted a stack of read-write heads that write information to the disk surfaces and read information from the disk sur- faces. Remember when we were discussing the importance of saving often when working on a computer? The save process reads information stored temporarily in RAM and transports the information to the disk controller, which in turn, under the guidance of the operating system, transmits the information to the write heads; they, in turn, write the bits to the disk surface by magnetizing the iron oxide surface. Of course, once the bits have been written to the disk, it's important to keep track of where the information is stored on the disk. This is a function of the operating system. Have you ever inserted a floppy into a drive or (far less fun) a new hard drive into a computer as I recently had to do, and had the computer ask you if you're sure you want it to format the drive? In order to keep track of where files are stored on a disk, whether a hard drive, a CD, a zip drive, or a floppy, the operating system marks the disk with a collection of road markers that help it find the "beginning" of the disk so that it can use that as a reference. Obviously there is no "begin- ning" on a circle, by design; by creating an arbitrary start point, however, the operating system can then find the files it stores on the drive. This start point is called the file allocation table, or FAT; if the FAT goes away for some reason the operating system will not be able to find files stored on the drive. When my hard drive failed, my initial indication that some- thing bad was about to happen was an ominous message that appeared during the boot cycle that said "UNABLE TO FIND FAT TABLE." Figure 5-4 Close