Hard Disk

2.2 Hard Disk

Hard disk is a type of magnetic disk. It is also called fixed disk because it is fixed in the system unit. A hard disk consists of several circular disks called platter sealed inside a container. The container contains a motor to rotate the disk. It also contains an access arm and read/write head to read and write data to the disk. The platters are used to store data. AA platter in a hard disk is coated with magnetic material.

The hard disk used in computers spin at the speed of 5400 to 15000 revolutions per minute (rpm). The speed at which the disk spins is a major factor in its overall performance. The high rotational speed allows more data to be recorded on the disk surface.

Characteristics of Hard Disk

Some important characteristics of hard disk are as follows:

·         Hard disk provides large storage capacity. The capacity of personal computer hard disk is from 160 GB to 2 TB and more.

·         It is much faster than floppy disks.

·         It is the primary media for storing data and programs.

·         It is more reliable than floppy disk.

·         Data stored on hard disk is safer than floppy disk.

2.2.1 Hard Disk Performance

The following factors affect the performance of hard disk:

·         Seek time or positioning performance: The time required by read/write head to reach the correct location on disk is called seek time. It is often used with rotational speed to compare performance of hard drives. It is measured in milliseconds (ms).

·         Spindle speed or transfer performance: It is the speed at which the drive transfers data. It is measured in rotations per minute (RPM).

·         Latency: It is the time required by the spinning platter to bring the desired data to read/write head. It is measured in milliseconds

2.2.2 External and Removable Hard Disks

An external hard disk is a separate hard disk that is connected to the system unit with cable, USB port or Fire-wire port. Some hard disks can also communicate with system unit wireless. The entire hard disk is enclosed in a sealed cased. The storage capacity of external hard disk is up to 4 TB and more.

 A removable hard disk is a type of hard disk that can be inserted and removed from a drive. The drive can be built in the system unit or the disk can be connected with cable, USB port or Fire-wire port on system unit. The removable hard disk drive is used to read and write data on the removable hard disk is up to ITB and more.

The data transfer rate of external and removable hard disks is slower than internal hard disks. However, there are different advantages of these disks over internal hard disks.

Some important advantages of external and removable hard disks are as follows:

·         These disks can be used to transfer a large number of files from one place to another.

·         These disks can be used to backup important files or entire internal hard disk.

·         These disks can store a large number of audio and video files easily.

·         These disks can be removed from computer and locked at a secure place for the protection of data.

·         These disks can be used to increase storage space of the computer without opening the system unit.