INTERNAL COMPONENTS OF A HARD DISK

It should first be mentioned that the internal components of a hard disk are very sensitive to dust, debris and fingerprints.  It only takes a small amount of dust on the surface of the platters to destroy all of the data on the hard disk.  For this reason,
a hard disk should never be opened unless in a clean room environment. 

Drive Casing
The drive casing is the rectangular shaped box that holds all of the internal components of the hard disk.  A cover mounts
to the casing using multiple screws (for the illustration above, the cover has been removed).

Spindle
The spindle rotates the platters at a certain speed measured in RPM. 

Actuator Arm
The actuator arm (also called the read/write arm) contains read/write heads near the end of the arm.  It is the actuator arm
that helps position the read/write heads at the correct location on the platter to read the data.  The heads never actually
touch the platters when accessing the data.  They function at approximately 5 microns above the surface of the platter. 

Platters
In the center of the hard disk, there are platters which hold all of the data on the hard disk.  A disk can contain one or more platters depending on the capacity.  Platters are round with a hole in the center- similar to a record used on a record player.  A spindle with a motor holds the platters together and rotates them at a certain speed measured in RPM (revolutions per
minute).  This creates air pressure that lifts the read/write heads off the platters.

Actuator
The actuator moves the actuator arm to the correct position on the platters using voice coils motivated by electric currents. 
When no electric current is being received, the actuator causes the actuator arm to place the read/write heads in the parked
position.

Ribbon Cable
This cable attaches the read/write heads to the controller board.