Working Of A Hard Disk Drive

Hard Disk Drives are permanent storage devices used in computers, laptops, netbooks and more. Whenever you save a file on your laptop or computer, it is actually stored in these hard disks. The programs that run on your laptop also have their code stored in the hard drives. The data in these HDDs will be retained for very long periods of time and can be retrieved, erased and re-written easily. The information will be retained even after the laptop or computer is shut down.

Construction of a Hard Drive:-
A typical hard drive unit consists of the following components:-
•    A Platter – A central spindle holds one or more platters or circular disks which are made of aluminium or glass. These platters are coated with a magnetic material. Data is recorded onto these circular discs or read from them. They rotate at high speeds around the spindle. This magnetic film is divided into magnetic regions. Further each region consists of grains. These grains are magnetized to store data.
•    An Arm with read/write heads – This arm moves radially across the platter to either read or write data to it. There are 2 heads per arm. One to read and one to write.
•    Electronic circuit for controlling various activities – The electronic circuit control the reading and writing process. They also control the motors and data movement to and from other parts, like the CPU.
•    Motors – There are usually 2 motors for controlling a hard drive. One that rotates the platter and the other which moves the arm over the platter.

How Do Hard Disks work?
As mentioned earlier there is a motor that rotates the platter about the spindle. The rotation speed is what is usually seen when specifying hard drives. For example – 5400 rpm (rotations per second) or 7200 rpm. When the platter is rotating, the arm moves along the radius of the platter. The writing head writes data on to the disk or the reading head reads data from the disk as this happens.

The writing head will usually consist of an electromagnet. An electromagnet consists of an iron core with an electric wire wound around it. When an electric current passes through the wire, it magnetizes the iron core proportionately. This magnetic field is used to magnetize the grains on the platter. The grains can retain the magnetism for a really long period of time. While reading back the data, this magnetic field is again converted back to electric signals.

Hard disk drives are usually available in different storage space capacities in Laptops. The memory capacity or hard drive capacity can be increased by using more than one platter and hence arms as well.