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in this article I am tell about What is Hard Disk ,its types and Working. In this article is very useful of computer science students.
Table of Contents
Hard Disk
- A hard disks are online storage device
They are used as a secondary memory for mass storage of information permanently.
They store program data operating system compilers ,application program etc.
A hard disk is made of aluminum or other metal or metal alloy or glass base with a thin coating of magnetic material(iron oxide) over- This standard hard disks size are 3.5,2.5,2,1.8 and 1.3 inch diameter.
- 3.5 inch diameter disk are commonly used.
- Digital information stored on the magnetic coating (Film) by applying current by applying current pulses of suitable polarity to magnification of the very small area of magnetic film which comes under the read/write head.
Types Of Hard Disk
There are two type of Hard disk
1.Longitudinal Recording:-
In longitudinal Recording the magnetized region are oriented parallel to the disk surface along the track.
2.Vertical Recording
In vertical Recording the magnetized region are vertical to the disk surface
The vertical recording stores many times more data as compared to longitudinal recording.
Working Of Hard Disk
- During read operation a voltage is induced in the coil of the read/write head due to the changes in the magnetic filed in the vicinity of head. The coil now serves as a sensing coil.
- Below fig shows a read write head
- Hard disk and read/write head are placed in a sealed, air filtered enclosure. This technology is called Winchester technology .The disk used in this disk is called Winchester Disk
- A hard disk is a surface device.
- Its surface is divided into a number of concentric tracks and each track is divided into a number of sector as show in fig below.
- Each track is divided into a number of sectors. track and sector do not have physical existence on the surface of a disk. Data are stored in hard disk serially on each track. The speed of hard disk drive lies in the range of 5400-15000 RPM.
- The data transfer rate is 25 to 700 MB/S.
Seek Time
- The time required to move the read/write head to the specified track is called seek time.
Latency Time
- It is the time required to rotate the specified sector under the head.
- The access time of head disk is about 5 to 15 M sec.