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
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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
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