Hardware Reference
In-Depth Information
Figure 2.1: Tracks, Sectors, and Actuator.
circles, known as the tracks [Figure 2.1]. There can be as many as 100,000
tracks on each surface of a disk used in a 3
2
inch HDD. Recording (or writing)
of the bits and playback (reading) is performed with a write head and a read
head, respectively. The disks are spun at a precisely controlled speed when the
operation of writing or reading is performed. The two heads are fabricated on
a single slider, which is epoxy-bonded to a stainless-steel or aluminium gimbal
at the end of a long and thin structure known as the suspension arm.
Each surface of an HDD is accessed by a dedicated head slider mounted
at the tip of a suspension arm. Suspension arms carrying sliders for different
surfaces are attached to a single actuator, driven by a motor popularly known
as Voice Coil Motor or VCM. The movement of the head sliders between any
two tracks is effectuated by the VCM actuator. It also regulates the position
of the head over the center of a track while data is being written on or read
from that track. As the disk spins while the head is regulated over the center
of a track, the read/write head scans the entire track in one revolution of the
spindle. It is desired to have the head positioned above the track-center with
minimum variance before reading recorded data off the disk or writing new
data on the disk can be performed. The tracking error during regulation of
head position must be less than 10% of the track pitch (distance between two
adjacent tracks) for data writing.
When the disk spins at high speed, an ABS is formed between the slider
and the spinning disk that makes the slider float above the disk surface. The
suspension arm is designed such that it produces precise load force and damp-
ing required by the slider to interact with the ABS formed. The movement of
the slider perpendicular to the disk surface is self-regulated by the interaction
between ABS, load force and damping. The movement of the slider in direction
