1.2.3 Mechanical and Electronic Components
The drive enclosure is the external casing of the hard disk drive. It provides
features for mounting the drive in the drive bay of the host system, and sup-
ports other components of the HDD such as spindle motor, actuator, PCB etc.
There are two parts of the enclosure - top cover and base plate.Alcompo-
nents are assembled on the base plate. Enclosure is then covered using the top
cover. Gasket is used to seal the contact between base plate and top cover.
The environment inside the enclosure must be maintained clean. Any particle
at the head-disk interface can cause abrasion of the disk resulting in loss of
data and increase in number of particles. Therefore, assembly of the drive is
done in a clean room to ensure particle-free enclosure. Particles created during
the operation of drive by sudden contacts between disk and slider are thrown
out of the spinning disk by the centrifugal force and eventually trapped in the
fi lter, placed in the empty space inside the enclosure.
A special feature of both the base casting and top cover is the crash stop.
These are small mechanical protrusions from the base plate and top cover used
to restrict the movement of the actuator beyond the desired space.
Electronic components of an HDD can be categorized according to the
1. Electronics for reading/writing also known as the channel electronics
2. Electronics for spinning the disks and positioning of the read/write head
also known as the servo channel
3. Electronics for controlling various operations (such as read data, write
data, transfer data between HDD and host etc) of the disk or the disk
4. Electronics for interface with the host system, and
5. RAM, ROM etc.
Several of these functional components are often combined in a single chip. As
a result, we do not see many ICs on the PCB (printed circuit board) of an HDD.
One IC that is not placed on the PCB but is kept inside the drive enclosure
is the pre-ampli fi er. It is put as close to the read/write heads as possible to
avoid ampli fi cation of noise, and is mounted on the fl ex-cable that carries signal
between heads and PCB. The output of the preampli fi er is suﬃciently large
ensuring good signal-to-noise ratio at the input of the PCB.