Hardware Reference
In-Depth Information
Forexample,analternator,whichisatypeofelectricalgeneratorusedinautomobiles,op-
eratesbyrotatingelectromagnetsonashaftpastcoilsofstationarywireconductors,which
consequently generates large amounts of electrical current in those conductors. Because
electromagnetismworkstwoways,amotorcanbecomeagenerator,andviceversa.When
applied to magnetic storage devices, this two-way operation of electromagnetism makes
it possible to record data on a disk and read that data back later. When recording, the head
changes electrical impulses to magnetic fields, and when reading, the head changes mag-
netic fields back into electrical impulses.
The read/write heads in a magnetic storage device are U-shaped pieces of conductive ma-
terial, with the ends of the U situated directly above (or next to) the surface of the actual
data storage medium. The U-shaped head is wrapped with coils or windings of conduct-
ive wire, through which an electric current can flow (see
Figure 8.3
)
. When the drive lo-
gic passes a current through these coils, it generates a magnetic field in the drive head.
Reversingthepolarityoftheelectric currentalsocausesthepolarityofthegeneratedfield
to change. In essence, the heads are electromagnets whose voltage can be switched in po-
larity quickly.
Figure 8.3
A magnetic read/write head.
