What is Hard disk drive? Function & Defination

What is Hard disk drive?

The hard of a computer stores all software installed on that computer and also stores all data files used by that software. This stores all data that user created and downloaded from Internet. A hard disk drive is a permanent storage device rather than Random Access Memory. If we turn off our computer our data is safely stored on the hard drive.

A hard disk drive is also known as hard disk, fixed disk or hard drive. It is firstly introduced by IBM in 1956, HDDs became the dominant secondary storage device for general-purpose computers by the early 1960s. More than 200 companies have produced HDDs historically, though after extensive industry consolidation most current units are manufactured by Seagate, Toshiba, and Western Digital. As of 2016, HDD production (in bytes per year) is growing, although unit shipments and sales revenues are declining. The primary competing technology for secondary storage is flash memory in the form of solid-state drives (SSDs), which have higher data-transfer rates, higher areal storage density, better reliability, and much lower latency and access times. While SSDs have higher cost per bit, SSDs are replacing HDDs where speed, power consumption, small size, and durability are important.

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How is a hard drive connected to a computer?

An internal hard drive is connected to the computer using a data cable (IDE or SATA) that connects to the motherboard and a power cable that connects to the power supply.

Now the question is how data is stored in hard drive

In a hard drive, there's just a large shiny, circular "plate" of magnetic material called a platter, divided into billions of tiny areas. Each one of those areas can be independently magnetized (to store a 1) or demagnetized (to store a 0). Magnetism is used in computer storage because it goes on storing information even when the power is switched off. If you magnetize a nail, it stays magnetized until you demagnetize it. In much the same way, the computerized information (or data) stored in your PC hard drive or iPod stays there even when you switch the power off.

The platters are the most important parts of a hard drive. As the name suggests, they are disks made from a hard material such as glass or aluminium, which is coated with a thin layer of metal that can be magnetized or demagnetized. A small hard drive typically has only one platter, but each side of it has a magnetic coating. Bigger drives have a series of platters stacked on a central spindle, with a small gap in between them. The platters rotate at up to 10,000 revolutions per minute (rpm) so the read-write heads can access any part of them.

There are two read-write heads for each platter, one to read the top surface and one to read the bottom, so a hard drive that has five platters (say) would need ten separate read-write heads. The read-write heads are mounted on an electrically controlled arm that moves from the centre of the drive to the outer edge and back again. To reduce wear and tear, they don't actually touch the platter: there's a layer of fluid or air between the head and the platter surface.

How data is read and write in hard drive

When your computer stores data on its hard drive, it doesn't just throw magnetized nails into a box, all jumbled up together. The data is stored in a very orderly pattern on each platter. Bits of data are arranged in concentric, circular paths called tracks. Each track is broken up into smaller areas called sectors. Part of the hard drive stores a map of sectors that have already been used up and others that are still free. (In Windows, this map is called the File Allocation Table or FAT.) When the computer wants to store new information, it takes a look at the map to find some free sectors. Then it instructs the read-write head to move across the platter to exactly the right location and store the data there. To read information, the same process runs in reverse.

With so much information stored in such a tiny amount of space, a hard drive is a remarkable piece of engineering. That brings benefits (such as being able to store 500 CDs on your iPod)—but drawbacks too. One of them is that hard drives can go wrong if they get dirt or dust inside them. A tiny piece of dust can make the read-write head bounce up and down, crashing into the platter and damaging its magnetic material. This is known as a disk crash (or head crash) and it can (though it doesn't always) cause the loss of all the information on a hard drive. A disk crash usually occurs out of the blue, without any warning. That's why you should always keep backup copies of your important documents and files, either on another hard drive, on a compact disc (CD) or DVD, or on a flash memory stick.