Hard disks are commonly used as secondary storage media in micro computers and large computers. A Hard disk is made of metallic disk coated with metallic oxide (iron-oxide) on both sides. The hard disk is permanently fixed in a drive unit in case of microcomputers. To increase the storing capacity, several disks (or platters) are packed together and mounted on common drive to form a disk pack.
The individual disks have some inter disk spacing to allow the access arms with read write heads to move in and out. The disk drive units has more than one access arms. Each access arm has two read/write heads. One of the heads on the access arms read/write data on the lower surface of a disk while the other head of the same access arm reads/writes data on the upper surface of the next adjacent disk positioned downwards. In general a disk pack of n number of disks will have (n-1) access arms, 2(n-1)recording surface and 2(n-1) read write needs.
The disk pack is contained in an airtight, dust free container. The read/write heads and access mechanisms are also sealed with the disks. The speed of rotation is about 3600 r pm (revolutions per minute).
The hard disk can store information at a faster rate compared to floppy disks. Similar to floppy disks, a hard disk is also divided into tracks and sectors. Generally, hard disk can have 200 to 1000 tracks per surface. Most of the hard disks contains 17 sectors per track the access time is about 20 millisecsnals.
The hard disks are available in different sizes :8 inch, 5.25 inch, 3.5 inch. It does not make physical contact with the disk surface.
To protect the hard disks heads few inner most tracks are lubricated to serve as parking zone (or landing zone) to provide safe landing of the heads.
Reading and writing :
The hard disk drive also has a read/ write head that moves over the desired track to read data from or write data onto the disk. As mentioned above, read/write head along with access arm does not physically touch the disk surface. It floats above the surface of the disk and detects the data (magnetized data).
A hard disk can store much more data than the flexible disk of the same size. An 8 inch hard disk could store 20 M.bytes whereas the same size floppy disk could store only 1 M.Bytes. The hard disks are useful in word processing and other applications where large volume of files or data are to be kept.
The individual disks have some inter disk spacing to allow the access arms with read write heads to move in and out. The disk drive units has more than one access arms. Each access arm has two read/write heads. One of the heads on the access arms read/write data on the lower surface of a disk while the other head of the same access arm reads/writes data on the upper surface of the next adjacent disk positioned downwards. In general a disk pack of n number of disks will have (n-1) access arms, 2(n-1)recording surface and 2(n-1) read write needs.
The disk pack is contained in an airtight, dust free container. The read/write heads and access mechanisms are also sealed with the disks. The speed of rotation is about 3600 r pm (revolutions per minute).
The hard disk can store information at a faster rate compared to floppy disks. Similar to floppy disks, a hard disk is also divided into tracks and sectors. Generally, hard disk can have 200 to 1000 tracks per surface. Most of the hard disks contains 17 sectors per track the access time is about 20 millisecsnals.
The hard disks are available in different sizes :8 inch, 5.25 inch, 3.5 inch. It does not make physical contact with the disk surface.
To protect the hard disks heads few inner most tracks are lubricated to serve as parking zone (or landing zone) to provide safe landing of the heads.
Reading and writing :
The hard disk drive also has a read/ write head that moves over the desired track to read data from or write data onto the disk. As mentioned above, read/write head along with access arm does not physically touch the disk surface. It floats above the surface of the disk and detects the data (magnetized data).
A hard disk can store much more data than the flexible disk of the same size. An 8 inch hard disk could store 20 M.bytes whereas the same size floppy disk could store only 1 M.Bytes. The hard disks are useful in word processing and other applications where large volume of files or data are to be kept.
Hi dear,
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