It is a data storage device and is made up of a thin circular discs, called "Platters", which are coated on both the sides by Magnetic Material. A Disk pack may consist of number of Platters and are mounted on a central shaft that rotates them in same direction with same speed.The Data is written or accessed in a random manner and individual blocks of data can be stored or retrieved in any order rather than just sequentially.It is connected to computer using different interfaces such as IDE, SATA or SCSI.
Information Storage: In HDD information is stored on all surfaces of platters except upper and lower surface of top and bottom platters respectively. thus,a disk with 5 disk platters will have 8 recording surfaces. Each plotter is consist of no. of invisible concentric circles which are called tracks. A set of such corresponding tracks in all the surfaces is called cylinder. Tracks are further divided into sectors. * bit EBCDIC code is used for the information storage.The Information is stored in form of invisible magnetic spots. The Presence of magnetic spot represents binary 1 and absence represents binary 0.
The Outer tracks has greater circumference then inner tracks but each track consist of same no. of characters.Hence the data density of outer tracks is less as compare to inner tracks.
Read /Write Operation: HDD uses two types of Head technologies for read and write operation.
i)Fixed Head
ii)Movable Head
Fixed Head: In Fixed Head Technology separate head is used per track and there is no movement.This makes data Read /write Operation Fast. But this also results in additional space requirement for heads.This results in less no. of platters per HDD and less storage capacity.
In Movable Head Technology Single head is used for per platter surface.This head moves in or out for read/ write operations in all tracks.
Access Time: Access Time is dependent on the mechanical nature of rotating disks and moving heads.The time taken by the head to travel the tracks that contains data is called seek time and the time taken by the sector to come under the head correctly is called latency time.Therefore the average access time is the sum of seek time and latency time.
Information Storage: In HDD information is stored on all surfaces of platters except upper and lower surface of top and bottom platters respectively. thus,a disk with 5 disk platters will have 8 recording surfaces. Each plotter is consist of no. of invisible concentric circles which are called tracks. A set of such corresponding tracks in all the surfaces is called cylinder. Tracks are further divided into sectors. * bit EBCDIC code is used for the information storage.The Information is stored in form of invisible magnetic spots. The Presence of magnetic spot represents binary 1 and absence represents binary 0.
The Outer tracks has greater circumference then inner tracks but each track consist of same no. of characters.Hence the data density of outer tracks is less as compare to inner tracks.
Read /Write Operation: HDD uses two types of Head technologies for read and write operation.
i)Fixed Head
ii)Movable Head
Fixed Head: In Fixed Head Technology separate head is used per track and there is no movement.This makes data Read /write Operation Fast. But this also results in additional space requirement for heads.This results in less no. of platters per HDD and less storage capacity.
In Movable Head Technology Single head is used for per platter surface.This head moves in or out for read/ write operations in all tracks.
Access Time: Access Time is dependent on the mechanical nature of rotating disks and moving heads.The time taken by the head to travel the tracks that contains data is called seek time and the time taken by the sector to come under the head correctly is called latency time.Therefore the average access time is the sum of seek time and latency time.
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