Figure 1.2: Typical components found in HDD.
1.2.1 Head and Disk
Data is recorded on a continuously spinning disk made of aluminum or glass
and coated on both sides with a thin layer of magnetic material. The disk is
mounted through a hole at the center on the shaft (spindle) of a motor that
spins the disks. In desktop application, the disks are spun at 6,000 or 7,200
RPM. The spinning speed can be 10,000 RPM or beyond in high performance
HDD. Disk is coated with several layers of other materials. Details of these lay-
ers can be found in any textbook on magnetic recording such as  and .
Two separate elements, the write and read heads, are used for writing data to
or reading data from the disks. These two heads are fabricated together on a
larger structure called the slider that serves several important purposes. The
slider provides electrical connectivity to both heads, and helps to place the
read and write heads in close proximity to the magnetized bits by flying over
the surface of the spinning disk. Well de fi ned aerodynamic surface is created
on the surface of the slider facing the disk to achieve the desired fl ying charac-
teristic. The air moving along with the spinning disk and entrained between
the disk and the slider's aerodynamic surface produces an air bearing that
makes the slider fl oat.
The surface of the disk must be very smooth to produce uniform readback
signal from the heads fl ying few nanometers above the disk. However, smooth
disk gives rise to a different kind of problem. As no air bearing is formed