HDDs were originally developed for use with computers but their applications have expanded beyond computers to include digital video recorders, digital audio players, personal digital assistants, digital cameras and video game consoles.



All hard disks share the basic structure. A typical HDD design consists of one or more flat circular disks called platters, on which magnetised data is recorded. Traditionally, platters were made of a light aluminum but newer technology uses glass and/or ceramic platters because they can be made thinner and have better heat resistance.

Most drives have at least two platters and more platters mean larger storage capacities. Each platter is magnetized on each side, so a drive with 2 platters has 4 sides to store data. The platters are separated by disk spacers and clamped to a rotating spindle that turns all the platters in unison at a constant rate ranging from 3,600 to 7,200 RPM.

Information is written on a platter as it rotates past mechanisms called read-and-write heads.They operate very close over the magnetic surface. The read-and-write head is used to detect and modify the information immediately under it. There is one head for each magnetic platter surface on the spindle, mounted on a common arm.

When one head is over a track, all the other heads are at the same location over their respective surfaces. Typically, only one of the heads is active at a time, reading or writing data. When not in use, the heads rest on the stationary platters at a predetermined position called the landing zone. When in motion the spinning of the platters create air pressure that lifts the heads off the platters.

Hard disk drives are considerably stable medium for data storage with good memory. They, however, have some typical shortcomings leading to data loss:

1. Head Crash: The space between the platter and the head is so minute that even one dust particle or a fingerprint can disable the spin and lead to a head crash. It is a failure of the disk in which the head scrapes across the platter surface, often grinding away the thin magnetic film causing data loss.

It is the main cause of data loss from the hard disk. Head crashes can be caused by external contamination, electronic failure, sudden power failure, physical shock, wear and tear, corrosion, or poorly manufactured platters and heads.

In event of a hard disk crash the user should immediately stop working on the computer. He should not run a programme, write mails or browse the net or even install DIY software. All these activities create new files and can overwrite the existing files. Any overwritten data is lost forever. He should immediately call a data recovery company. It needs expertise and experience to retrieve any data from a crashed hard disc and only professionals can do a good job of it

2. Software Errors: Hard disks can loose data due to software errors often triggered by the users themselves. These include an accidental deletion of a file and emptying of recycle bin by mistake. Another software error could be due to virus attack on the system while down loading data from internet or through copying of corrupt CDs.

3. Reformatting: A lot of times hard disks lose data during reformatting of the disk. Format means to prepare a storage medium, usually a disk, for reading and writing. When we format a disk, the operating system erases all bookkeeping information on the disk and creates new internal address tables that it later uses to locate information. All the data on the drive can be lost if the reformatting attempt fails. Therefore it is essential to take a data backup before reformatting a hard disk drive.

Most major hard disk vendors now support self-monitoring, analysis, and reporting technology (S.M.A.R.T.), which attempt to alert users to impending failures. However, not all failures are predictable. Normal use eventually can lead to a breakdown in the fragile structure of the device, making it essential for the user to periodically back up data on a separate storage device. Failure to do so can lead to data loss. While it may be possible to recover lost information, it is normally an extremely costly procedure, with no guaranteed success in the attempt.