Figure 1.3: Spindle with disks showing data storage area.
when the disk is stationary, the slider touches the disk surface and a stiction
force is produced. Smoother the disk surface more is the stiction between the
slider and the stationary disk. The stiction between sliders and disks opposes
the applied torque during the spinning up of the spindle, and large starting
current is required to overcome this torque. This problem was solved in the
earlier drives by creating appropriate texture on a small annular ring, known
as landing zone, on the disk near the center hole. The sliders are pushed to
the landing zone before the spindle is spun down so that they rest on the
textured surface when the drive is spun up next time. The area of the landing
zone can not be used for data storage. An alternative method, the Dynamic
Load/Unload, was later adopted to solve the problem of stiction between head
and disk . This method avoids contact between sliders and stationary disks
by bringing the sliders out of the disk surface prior to spinning down. A lift
tab extending from the arm engages a ramp structure as the actuator moves
beyond the outer radius of the disk. The ramps lift ('unload') the heads from
the disk surfaces as the actuator moves to the parking position. Starting and
stopping of the spindle motor occurs only with the heads in this unloaded
state. During spin up, the actuator arm is pushed over the ramp after the disk
attains the speci fi ed speed so that the sliders fl y.
There is no need to reserve an area for landing zone when dynamic load/unload
is used. However, a small ring near the spindle shaft is not used for storage of
data due to many other factors such as limit of accessibility by the read/write
head, EMI (electro-magnetic interference) generated by the motor coils etc.
The innermost track on the disk surface used for storing data is known as the
ID (inner diameter ) track (Figure 1.3). The OD (outer diameter ) track is cre-
ated as close as possible to the edge of the disk. However, the magnetic coating
in the region near the edge is often not as uniform as in the inner region. The
quality of the magnetic layer must be taken into consideration while deciding
the radius of the OD track.