To review, multiply bytes (5 12) times sectors (15) times
tracks (80) times sides (2). This gives the total capacity
of the diskette, 1.2M bytes.
Write Protect Feature.— Like all other media,
floppy disks/diskettes must also have a way of being
protected from a user accidentally writing on them.
This is accomplished with a write-protect notch (or
cut-out) located in the upper right-hand corner of the
plastic jacket (see figure 1-19). Whether or not the
write-protect notch is covered to protect the data on the
diskette depends solely on the disk drive manufacturer.
For example, on most systems using 5 1/4-inch
diameter diskettes, covering the write-protect notch
makes it impossible to write on the disk’s surface.
However, the opposite is true on systems using 3 1/2-
inch diameter diskettes. Uncovering the write-protect
notch makes writing impossible. In short, find out
which is which on your particular system before you
accidentally wipe out an entire diskette’s data.
Floppy Disk Drives.— Floppy disk drives are
manufactured to read and write data in one of several bit
densities for both single- and double-sided diskettes. A
single-sided disk drive can only read a single-sided
diskette. However, a double-sided disk drive, like the
one shown in figure 1-20, can read both a single-sided
and a double-sided diskette.
H A R D D I S K S A N D H A R D D I S K
DRIVES.— Although most microcomputer systems
you will be working on use some type of floppy disk
drive, you should also be aware that all micros also
contain a small sealed unit called a Winchester disk or
hard disk drive. Unless the disk drive is an external
type unit, you might never know it was there. Floppy
disk drives are easy to spot; all you have to look for is the
drive’s door, that open slot where you insert the diskette.
Hard disk drives, on the other hand, are normally sealed
Figure 1-20.—A floppy disk drive being removed from system
unit.
Figure 1-21.—Internal hard disk drive mounted on disk drive
chassis.
units that can be tucked away just about anywhere.
Generally, you will find them inside the system unit
(figure 1-21) in the space occupied by one of the floppy
drives.
Hard disk drives provide you with many
timesaving features not available nor possible with the
floppy disk drives.
These include increased access
speeds, greater storage capacity (up to 8 gigabytes [GB]
of storage), and overall convenience. Working with
hard disk is much easier because you can quickly end
one program and start another, all through the operating
system.
Hard disk units consist of rigid metal platters that
are tiered or stacked.
In most cases, the disks
themselves are not removable, and for this reason can be
hermetically sealed in the storage unit along with the
access mechanism that contains the read/write heads.
Because this type of disk drive is completely sealed and
free from air contamination, the read-write heads can be
positioned to within 20 millionths of an inch from the
surface of the disk. This also allows the disk to be
rotated at a high rate of speed-typically, 3600
revolutions per minute. Hard disks also comes in two
sizes (diameters): 5.25 inches, and 3.50 inches, with
3.50 being the most popular. Their storage capacities
range from 500 megabytes to 8 gigabytes, with the
majority in the 1.2- to 2-gigabyte range.
As mentioned earlier, hard disks can be placed
internally within the system unit, like the one shown in
figure 1-21, or externally as a detachable unit, as shown
in figure 1-22. You may have also noticed that the disk
drive shown in figure 1-22 is a portable hard drive in
that the hard disk is removable. The hard disks and
read/write mechanism are enclosed within a rugged
case. The result is a self-contained hard disk you can
insert like a floppy and remove for reasons of security.
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