Optical disk

Optical disk is a secondary storage unit which can store extremely large amount of data in a limited space. It is a random access system which consists of a rotating disk which is coated with a highly reflective material. For recording and retrieving data, laser beam technology is employed.  For this reason, optical disks are also known as laser disks. Optical disk has one long spiral track which starts at outer edge and spirals inward to the center. This is a main difference between this disk and magnetic disk where several concentric tracks exist. The optical disk track is split into various sectors.  Optical disks are very economical and with very small sizes ranging from 5 inches to 12 inches in diameter. The factors which influence storage capacity of an optical disk are number of sectors and number of bytes per sector. An optical disk has to be mounted on an optical disk drive before it can be used for reading and writing of information. This disk drive has provision to include all the mechanical, electrical and electronic components which facilitates reading and writing tasks. The different categories of optical disks are compact disk read only memory (CD-ROM), compact disk recordable (WORM-CD-R), compact disk rewritable (CD-RW) and digital video disk with read only memory (DVD-ROM). Since there is no mechanical heads in optical disks, damage due to crash is forbidden. The cost per bit of storage is very low and storage life is more than 30 years. Optical disks are ideal for storing and reading musical data. Optical disks are easy to handle, store and is portable. The main limitation of optical disk is its low data access speed. Optical disk drive mechanism is complicated and the option of reusability is forbidden in it.