Hardware Reference
In-Depth Information
For more information about AFC media and other advanced storage technologies,
see
Read/Write Heads
An HDD usually has one read/write head for each platter surface (meaning that each plat-
ter has two sets of read/write heads—one for the top side and one for the bottom side).
These heads are connected, or
ganged
, on a single movement mechanism. The heads,
therefore, move across the platters in unison.
Mechanically, read/write heads are simple. Each head is on an actuator arm that is spring-
loadedtoforcetheheadintocontactwithaplatter.Fewpeoplerealizethateachplatterac-
tually is “squeezed” by the heads above and below it. If you could open a drive safely and
lift the top head with your finger, the head would snap back down into the platter when
you released it. If you could pull down on one of the heads below a platter, the spring ten-
sion would cause it to snap back up into the platter when you released it.
Figure 9.10
shows a typical hard disk head-actuator assembly from a voice coil drive.
Figure 9.10
Read/write heads and rotary voice coil actuator assembly.
Whenthedriveisatrest,theheadsareforcedintodirectcontactwiththeplattersbyspring
tension,butwhenthedriveisspinningatfullspeed,airpressuredevelopsbelowtheheads
and lifts them off the surface of the platter. On a drive spinning at full speed, the distance
between the heads and the platter can be anywhere from 0.5 μ-inches to 5 μ-inches or
more in a modern drive.
