TOPIC 1—FUNDAMENTALS OF MAGNETIC DISKS AND DISKS DRIVES

Describe the physical characteristics of a fixed disk system Describe the data encoding methods used to write data on magnetic disks Describe disk interleaving effects on hard drive operations Explain the methods for recovering data from a fixed disk drive Explain the methods for preventing, detecting, and removing computer viruses from fixed disk systems Describe the precautions to be followed in handling and storing floppy disks, disk packs, and fixed disks — — — The popularity of disk systems has grown because of their speeds and large capacities to store data. Disks are generally thought of as random access memory devices, although this is not entirely true. To find data on a disk, first the read/write heads must seek a track, then wait while the disk spins to the desired sector. When the sector is reached, the heads can read or write data. In our study of disk storage devices, we explore what tracks and sectors areas well as the three major types of disk devices: floppy disk drives, disk file units, and fixed disk drives. We also examine how data is stored on a disk. When discussing floppy and fixed disk systems in personal computers, we are referring to IBM and compatible computers using Intel 80286 or greater microprocessor system. References to DOS refer to the Microsoft Disk Operating System (MS-DOS). TOPIC 1—FUNDAMENTALS OF MAGNETIC DISKS AND DISKS DRIVES Magnetic disks are generally termed as secondary storage for computer systems. They are used to temporarily hold data that is not immediately required for computer operations and to store programs that are not currently being executed. Through the years, magnetic disk data capacities have increased at tremendous rates. The first fixed disk drives had a capacity of just 5 megabytes. Today, fixed disk capacities are approaching several gigabytes. The same holds true for floppy disk drives. The original 8-inch floppy was a single-sided disk with a total capacity of 180 kilobytes. Today we have 3.5-inch floppy disks with a capacity of over 1.4 megabytes. Also, there are disk file units with removable disk packs that have capacities of several gigabytes. Disk file units are used with mainframe computer systems with large databases to speed up access times and to provide flexibility to system configuration. TYPES OF DISKS As mentioned previously, there are currently two types of disks: the hard disk and the floppy disk or diskette. Hard Disks Hard disks are divided into two groups, the disk packs used with disk file systems and the fixed disks. DISK PACKS. —Diskpacks contain large (usually 14”) platters. They are packaged in vertical stacks of up to 16 disks. Each disk surface is coated with a magnetic medium and can be used for data storage, although the top and bottom surfaces of the pack are usually used as protective surfaces. Disk packs are easily removed from the drive system. They have very large capacities and can store from 500 megabytes to 10-2