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Unformatted text preview: designers to provide increased data density of each square
inch of disk surface in these disk drives by reducing the distance between the read/write
head and the disk surface so that smaller magnetized spots can be precisely written and
then retrieved. Thus these disk drives provide higher storage capacity with the same size
disks and same number of disk surfaces. However, because of the sealed packaging, the
disks are not removable from their disk drives. Hence the storage capacity of these disk
systems is limited. Disk Controller
A disk drive is connected to and controlled by a disk controller which interprets the
commands for operating the disk drive. Since disk is a direct access storage device, the
disk controller typically supports only Read and Write commands. The disk address
consisting of surface number, cylinder/track number, and sector number needs to be
specified as parameters of the disk Read and Write commands. Often, a disk controller is
connected to and controls more than one disk drive. In this case, the disk drive number
must also be specified as a parameter of Read and Write commands so that the read/write
operation is carried out on the specified disk surface of the correct disk drive.
Types of Magnetic Disks
All magnetic disks are round platters. They come in different sizes, different types of
packaging, and can be made of rigid metal or flexible plastic. Based on these differences
there are many different types of magnetic disks available today. However, all of them
may be broadly classified into two types - floppy disks and hard disks. Floppy disks are
individually packaged in protective envelopes or plastic cases, whereas hard disks may be
packaged individually or in multiples in cartridges or contamination-free containers.
Depending on the type of packaging, hard disks are further classified into Zip/Bernoulli
disks, disk packs, and Winchester disks. The broad classification of magnetic disks is
shown in Figure 8.18. The four types of magnetic disks are described below.
Floppy Disks, Hard Disks
Zip/Bernoulli, Disks, Disk Packs
A floppy disk is a...
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This document was uploaded on 04/07/2014.
- Spring '14