Information Technology Reference
In-Depth Information
be unreadable. (Of course, the disk would work fine again when
you brought it home.)
A second potential reason could involve transportation. A disk
that used to work at home but won't work at school may have been
damaged in transit. For example, on the way to school or work, the
disk might have been placed near a magnetic field. (Perhaps the disk
was placed next to several credit cards with magnetic strips.) Or,
your disk could have been left on your car's dashboard in the hot af
ternoon sun, or squashed in your backpack. If the disk was dam
aged, then it will not work at school, and it will not work at home
either. Of course, you cannot check that when you are at school,
and should therefore investigate possible other causes for its mal
functioning.
A third potential reason that the disk won't work is more sub
tle. The reading and writing of material on disks depends on a spe
cific configuration of tracks and sectors. Some disks are identified
as “
double density
,” in which case the tracks and sectors might be
packed together more closely than for “
single density
.” Similarly,
some disks are “
single sided
,” whereas others are “
double sided
.”
That is, data may be stored on just one side of some disks, but data
may be placed on both sides of other disks. Both doubledensity
and doublesided formats provide mechanisms to store more infor
mation on a disk than would be possible with the traditional sin
glesided, singledensity format.
In reading and writing data on doubledensity disks, the disk
drive itself must be able to distinguish tracks that are close to each
other. For doublesided disks, the disk drive must be equipped with
read/write heads that can access both sides of the disk. In each case,
trouble would arise if data were stored in a doubledensity or dou
blesided format but the disk drive was not capable of handling that
format. (As a practical matter, drives that are sophisticated enough
to read doubledensity normally can also read singledensity.
Similarly, drives for doublesided disks also can read singlesided
ones.) If your disk drive at home uses a compressed format but the
computers at school or work do not, then your diskette at home
would not work there. Today, most computers with removable
disks can read doublesided, doubledensity diskettes.
The fourth potential reason involves a partial hardware mal
function. A disk drive requires the precise movement of read/write
