At the heart of the computer is a small processor that resides on the motherboard inside the CPU. This processor, that has millions of microscopic transistors, is one of the most important devices ever invented by man. It can carry out a phenomenal number of calculations, much more than the human brain can. This unbelievable computing power is controlled and channelled by an operating system without which the computer would remain just a dumb machine.

The operating system and the processor work as a team to run a variety of software packages. These are in turn tailor-made to execute various tasks as desired by the user. A computer in day-to-day use creates or modifies a huge amount of digital data which resides on the hard disk.

The hard disk is a small rectangular metal case that is sealed and made air-tight so that no dust particles or other contaminants can enter the assembly. Inside the case exists a row of vertically arranged platters. The entire row sits on a single spindle motor. The platter surface is coated with a thin magnetic paint on which is stored all digital data as a series of patterns.

The spindle motor spins the platters at a speed of about 150 revolutions per second. A read / write head suspended a sub-micron level above the platters carries an electro-magnet which reads, writes and modifies all data on the platter surface. When you shut the computer down, the read / write head moves over to a side away from the platters and is parked safely in its socket. When you switch on the computer, the platters start rotating and once they have achieved full speed, the read / write head moves from its parking space and hovers over the platters, accessing data as per the instructions of the operating system.

There is currently no storage media other than a hard disk that is fit enough to be used as a primary storage device for computers and laptops. There are many reasons for this. The biggest is that the hard disks offer random access to data stored on them. The entire surface of the platters remains exposed. The read / write head can access every millimetre of this surface and extract the desired data regardless of where it is stored. This random access is a blessing because, for the computer to be of any use, the data retrieval speed has to be matched by the data-crunching speed of the processor.

Contrast this random access to tape drives which offer sequential access. Data in a tape drive is stored on a long length of tape that is wound around two spools. The entire tape has to wind and unwind brushing past the stationary read / write head before a particular file can be accessed. That is why tape drives are good only for taking data backups.

Nothing can match hard drives in terms of the data holding capacity they offer. The commonly available hard disks have a capacity of 80, 160 and 240 GB. The high-end drives can have a capacity of 500 GB and above! The huge capacities that the hard disks offer along with random access that allows any data residing anywhere on the disk to be accessed instantly make them ideal data storage tools for devices which process a huge amount of data as a matter of routine.

Hard disks are quite reliable and can give trouble-free service for four or five years. However, they are still a complex piece of machinery and there is much that can go wrong. The common hardware errors relate to the read / write head becoming unhinged and crashing on the platter surface or parts such as spindle motor, circuit board and controller card developing some malfunction. Data can be lost due to software errors too such as file corruption, computer virus, reformatting of disk surface and accidental deletion of data by the user.

For the next five or six years, there is nothing on the horizon that can challenge the monopoly of the hard disk as the primary data storage media of computers and laptops.