§ These are the memories which use high intensity light signals to store and read data from the memory device.
§ These memories are highly reliable, compact in size and inexpensive compared to their capacity.
§ These memories are circulars in shape and divided into tracks, normally contain large number of tracks.
§ These disks are normally sequential storage direct access medium that is one can access any of the track on these disk directly.
§ These are mainly three optical types of memory in the market.
· CD ROM
CD ROM Disks:
§ This is the most popular types of optical disk in the market.
§ This was invented by Phillips Company; initially this memory was used for audio data storage, for recording and distributing music.
§ But later on CD become very popular medium to store and retrieve computer data because of its high capacity , high reliability and low cost.
§ Most of Compact Disks in the market are read-only type memories.
§ That is once the data is written on these disks then that cannot be altered.
§ CDs are inexpensive medium to store large amount of data, in fact one blank CD of approximately Rs/- 20 can store around 650 MB data, which is equivalent to storage of around 500 floppies.
§ CDs are used for storing all types of data like audio, video, text or any other type of business data.
§ Because of its low cost and high reliability, it is used as universal portable type of memory for distributing software and data from one place to other place.
§ Presently, CD’s manufacturer has also introduced the CD – R/W that is Compact Disk Rewriteable, which allows a CD to be written again and again like floppy.
§ CD- R/W is used just like the floppy but has the advantages of high capacity and more reliability than floppy.
§ With the popularity of internet and multimedia, the higher capacity storage mediums are required to share large volume of information in form of images and documents.
§ And CD and DVD storage mediums are playing very playing very important roles to share and exchange this information from one system to another.
§ In CD, a synthetic reflecting surface is used for data storage.
§ The data on CD is stored on multiple tracks with the help of laser light signals.
§ Over the years, The CD has gone through many technological changes; such as:
· CD- ROM
· CD – R/W
· CD -RW
§ The popular companies that manufacture CD-ROM drive, CD- writer are Samsung, Creative, HP and LG.
§ These are optical memories known as Write Once Read Many time’s disks.
§ These memories are like CD-R and used for storage of historical data, permanently.
§ These disks can store approximately 200 MB data in the text and image data form.
§ WORM disk is no more a popular disk; it has been replaced by more popular optical laser disks known as CD – R and DVD – R.