Figure 1.10: Schematic illustration of a disk surface with zoned-bit recording
1.4 Trend in HDD Industry
The disk drive industry has evolved through dramatic changes in the fi ve
decades of its existence. Demand for larger capacity, need to have smaller
dimensions for speci fi c applications, requirement of data transfer rate com-
patible for fast on-line applications etc are some of the driving forces behind
the extraordinary growth of this industry. Desire to have large capacity in a
smaller dimension is directly linked to the demand for ever increasing storage
density. Areal density and dimensions of the drive are two factors affected by
the mechatronics and control of actuator servomechanism, where as the design
and operation of the spindle motor has direct effects on the data transfer rate.
1.4.1 Areal Density Growth
The most obvious change that took place in the hard disk drive industry over
last four decades is the phenomenal increase in the storage capacity of HDD. As
recent as in early 1990s, a typical PC used to be shipped with an HDD capable
of storing approximately 100 megabytes of data. Today, even a computer
for home or personal use comes with HDD storage of 80 gigabytes or more.
Demand of storage capacity caused by larger size of programs and multimedia
data has driven the manufacturers to increase the capacity of their products.
While the capacity continued to increase, the price of HDDs experienced a
continuous fall. This was made possible by increasing the amount of data
stored on each surface of the disk, i.e., by increasing the areal density.
The fi rst hard disk drive (RAMAC) supported an areal density of 2000
bits/in 2 only. Today the density has escalated to a high 100 Gbits/in 2 ,which
is an increase by a factor of 5 million (Figure 1.11). This phenomenal increase
in areal density have been achieved by a coordinated efforts in improving all
aspects of the hard drive. Head technology has been continuously improved