Friday, March 18, 2011

What is a hard drive?

A hard disk is a storage device which is one of the most integral parts of a computer. Hard disk is a part of computer which contains the encoded information and stores various programs and files. This system operates digital storage in discs which are rapidly rotating magnetic surfaces. In a computer, the disk drive is one of the essential parts and is the primary file storage. The hard drive is so named in order to differentiate it from the diskette or floppy disk which has a lower storage capacity that hard disk. The hard disk drive is able to store a large amount of data in form of gigabytes while traditional floppy disks stored only 1.4 megabytes (now obsolete with the advent of the popular USB flash drive or memory with large storage capacity, durability, and reduced size). According to tech gurus and experts, the future of storage devices are high capacity USB Flash drives.

The hard disk is a series of discs or plates that are located within an outer cover. These covers, which are usually 2 or 4, although there may be up to 7, are made of aluminum or glass and whirling all the time, driven by a motor. The plates are read by the read/write head, which is a set of arms that are aligned vertically so that they can not move independently, but all at once. Each plate is read by two arms that have at their tips a read/write device and they read each side of the plate. Usually there are 8 heads for 4 covers. The heads never touch the plate, because it could cause much damage considering how fast they spin.

The discs consist of tracks, which are the circumference of each face, like a vinyl record. The heads move from the outer track, called track 0, to the inner track. The tracks are lined up in every disc. The set of vertically aligned tracks on each cylinder plate is called. The tracks are divided into sectors that do not have a fixed size. Normally, sectors are 512 bytes (the smallest units of memory).

The performance of a hard disk is measured by different factors. One is the access time, which is the time when the device starts to send data after receiving the order. The access time is the sum of seek time, latency, and time taken for reading and writing. The search time is that it takes the head to reach the target track. Latency is the time to wait for the disk to rotate until the desired sector passes through. Finally, the read/write time is the delay in locating the data controller, read and send new information to the computer. Another important factor is the hard disk transfer rate is the rate at which information is transferred to the computer after it reaches the desired track and sector.