The hard disk is a type of magnetic disk. It is also called a fixed disk because it is fixed in the system unit. A hard disk consists of several circular disks called platters sealed inside a container. The container contains a motor to rotate the disk. It also contains an access arm and read and write head to read and write data to the disk. The platters are used to store the data. A platter in a hard disk is coated with a magnetic material.
The hard disk used in computers spin at the speed of 5400 to 15000 revolutions per minute. 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 the hard disk are as follows:
- Hard disk provides large storage capacity.The capacity of personal computer hard disk is from 160 GB to 2TB and more.
- It is much faster than the floppy disk.
- 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 the floppy disk.
Hard disk performance
The following factors affect the performance of hard disk:
Seek time: it is also called positioning performance.It is the time required by reading and writes head to the correct location on the disk.it is often used with rotational speed to compare the performance of hard drives. It is measured in milliseconds.
Spindle speed: it is also called transfer performance. It is the speed at which the drive transfers the data.
Latency: it is the time required by spinning platter to bring the desired data to read and write head.
External and Removable Hard Disks
An external hard disk is a separate hard disk that is connected to the USB port on the CPU. Some hard disks can also communicate with the system unit wirelessly.
A remove able hard disk is a type of hard disk that can be connected to the system unit using USB port or firewire port.
There are some advantage s of remove able hard disks as follows:
- These can be used to transfer a large number of files from one place to another place.
- These can be used to backup important files.
- These can be used to store a large number of audio and video.
Miniature hard disks
These disks are very small hard disks.These disks are available in different size. The devices such as portable and smartphones have miniature hard disks. These
Provides more storage capacity than the flash memory.
Hard disk controllers
It consists of chips and electronic circuits. It also controls the transfer of data, instructions, and information between system and system unit.
There are 4 types of hard disk interfaces for personal computer which are as follows:
SATA stands for serially advanced technology attachment. It used for serial signals to transfers data, instruction and information. The main advantage of SATA is that cables are thinner, longer and higher. The external hard disks can use SATA interface that is much faster than USB.
EIDE stands for Enhanced Integrated Drive Electronics. EIDE is a device interface that used signals parallelly to transfer the instructions and data etc. The approximate data transfer speed of EIDE is up to 133 Mbps.
SCSI stands for Small Computer System Interface. It is used parallel signal and cannot support from 8 to 15 devices. SCSI can support hard disks, disk drives, printers etc.
4: Disk cache
It is used to improve hard disk performance.it is a type of ram program instructions and data that user is working with. When the CPU needs the information it first looks the cache from hard disk and if it doesn’t need the information it retrieves information from the hard disk.