PC Hardware A Beginner’s Guide

(^178) PC Hardware: A Beginner’s Guide
When the energized head passes over the recording media of the platter, the magnetic
field’s polarity is used to change the orientation of the magnetic particles in the media to
represent an electrical value. If the polarity of the head is changed, then the data stored on
the media will have a different electrical value. Reversing the electrical flow in the wire
wrapped around the U-shaped head changes the polarity of the magnetic field, which is
used to change the value of the platter’s media, and presto, data is written to the disk.
As discussed earlier, the material used to coat the disk platter is made of iron oxide.
On a new or erased disk, the magnetic field of each particle is randomly assigned, which
has the same effect of cumulatively canceling out the magnetic fields of its neighboring
particles. To the read/write heads, the disk has no recognizable patterns and looks blank.
As the read/write head passes over the disk, if the particles in one particular area are
aligned in the same direction, their cumulative magnetic fields will create a recognizable
pattern that the head will detect as a binary digit.
Flux
The read/write head uses magnetic flux to record data on the disk media.Fluxrefers to a
magnetic field that has a single and specific direction. As the disk surface rotates under it,
the read/write head uses a reversal in its polarity, called aflux reversal, to change the
alignment of magnetic particles on the disk surface. This is how data is recorded on the
disk. Simply put, the read/write head creates a series of flux reversals in an area called a
bitcell,whichisaclusterofmagneticparticlesusedtorepresentasinglebinarydigit(bit).
As illustrated in Figure 9-5, as the disk and bit cells rotate under or over the read/write
head, the head acts as a flux voltage detector. Each time it detects a flux transition, a change
from positive to negative, or the reverse, it sends out a voltage pulse. If no transition—that
is, no change in the polarity of the bit cell—is detected, then no pulse is sent. Notice how
these two activities can be matched to the 1s and 0s of binary data.
Figure 9-5. The read/write head acts as a flux transition detector