The C.D.-R.O.M. stands for Compact Disk-Read Only Memory. It is an optical R.O.M. which enables prerecorded data to be read. A laser beam is used to write into or read from C.D.-R.O.M. The C.D.-R.O.M. has very high storing capacity. The read/write head of C.D.-R.O.M. drive unit does not touch the disk surface, there is no risk of disk wear or head crash.
The manufactures themselves write data on C.D.-R.O.M. The C.D.-R.O.M. is made up of resin. It is coated with a material (e.g. aluminum) which will change when a high intensity laser beam is focused on it.
Reading and writing :
While writing, high intensity laser beam forms as tiny pit along the surface which represent binary bit 1. Absence of bit represents bit. While reading C.D.-R.O.M., the reflected laser is sensed by photo diode ( light sensitive semi conductor divide ). The intensity of reflected laser beam changes when the beam encounters pit (i.e. 1). A pit spreads light so that the photo diode receive little reflected light but the surface without pit reflects enough light to the photo diode.
Advantages of C.D.-R.O.M :
1. C.D.-R.O.M. has very high storing capacity.
2. They are relatively less expensive.
3. They have a long life ( at least 20 years ).
4. C.D.-R.O.M.'s can be removed from the drive.
5. They are comparatively reliable.
The major disadvantage of the C.D.-R.O.M. is that the access time ( time taken to read data ) is longer as compared to hard disks.
While manufacturing C.D.-R.O.M.s, a master disk is prepared in the beginning and they are produced in a mass scale after moulding a special plastic to the master disk. The C.D.-R.O.M.s use long spiral tracks to store data, the tracks are divided further into blocks.
The manufactures themselves write data on C.D.-R.O.M. The C.D.-R.O.M. is made up of resin. It is coated with a material (e.g. aluminum) which will change when a high intensity laser beam is focused on it.
Reading and writing :
While writing, high intensity laser beam forms as tiny pit along the surface which represent binary bit 1. Absence of bit represents bit. While reading C.D.-R.O.M., the reflected laser is sensed by photo diode ( light sensitive semi conductor divide ). The intensity of reflected laser beam changes when the beam encounters pit (i.e. 1). A pit spreads light so that the photo diode receive little reflected light but the surface without pit reflects enough light to the photo diode.
Advantages of C.D.-R.O.M :
1. C.D.-R.O.M. has very high storing capacity.
2. They are relatively less expensive.
3. They have a long life ( at least 20 years ).
4. C.D.-R.O.M.'s can be removed from the drive.
5. They are comparatively reliable.
The major disadvantage of the C.D.-R.O.M. is that the access time ( time taken to read data ) is longer as compared to hard disks.
While manufacturing C.D.-R.O.M.s, a master disk is prepared in the beginning and they are produced in a mass scale after moulding a special plastic to the master disk. The C.D.-R.O.M.s use long spiral tracks to store data, the tracks are divided further into blocks.
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