Hardware Reference
In-Depth Information
generates voltage when reading is when passing through a polarity or flux transition (flux
reversal).
In essence, while reading from the medium, the head becomes a flux transition detector,
emitting voltage pulses whenever it crosses a transition. Areas of no transition generate
nopulse.
Figure8.4
showstherelationshipbetweenthereadandwritewaveformsandthe
flux transitions recorded on a storage medium.
Figure 8.4
Magnetic write and read processes.
You can think of the write pattern as being a square waveform that is at a positive or neg-
ative voltage level. When the voltage is positive, a field is generated in the head, which
polarizes the magnetic media in one direction. When the voltage changes to negative, the
magnetic field induced in the media also changes direction. Where the waveform actually
transitions from positive to negative voltage, or vice versa, the magnetic flux on the disk
also changes polarity. During a read, the head senses these flux transitions and generates
a pulsed positive or negative waveform, rather than the continuously positive or negative
waveform used during the original recording. In other words, the signal when reading is 0
volts unless the head detects a magnetic flux transition, in which case it generates a pos-
itive or negative pulse accordingly. Pulses appear only when the head is passing over flux
transitions on the medium. By knowing the clock timing the drive uses, the controller cir-
