OPTICAL STORAGE

OPTICAL STORAGE

CD- ROM

CD-RW

DVD Disc

Magneto Optical

Working of CRT Monitor

Optical Disk

Optical disk is an electronic data storage medium from which data is read and written to by using a low-powered laser beam. It is flat, circular, plastic or glass disk on which data is stored in the form of light and dark pits. The laser beam reads the pits and the data can be accessed. There are three basic types of optical disks:
Read-only optical disks: The optical disks, which are recorded at the time of manufacture and cannot be erased. CD, CD-ROM, DVD-ROM, and DVD-Video are the read-only disks.
WORM:  WORM stands for write-once, read many. The optical disks that can be recorded by the user only once but cannot be erased. After they have been recorded once, they behave like a read-only optical disk CD-R, DVD-R, and WORM disks are write-once.
Rewritable/Magneto-optic disks: The optical disks that can be erased and written to with the new information. CR-RW, DVD-RAM, DVD-RW, and magneto-optic disks and Data play are rewritable. Rewritable disks use magneto-optic or phase change technology.
An optical disk offers many advantages over magnetic storage media.

• Highest storage capacity
• Low cost per Megabyte of storage
• Environmental condition tolerance
• High data stability
• Long media life

OPTICAL STORAGE DEVICES

1. CD-ROM:

CD-ROM: is an abbreviation of Compact Disc Read-Only Memory. A CD-ROM is a CD that contains computer data, which cannot be rewritten. In computers, CDROM is the most commonly used optical storage technology. CD-ROM is a compact disc that contains information, which is accessible by a computer. It is composed of polycarbonate plastic, thin reflective metal layers, made of aluminum and a lacquer coating. Data is stored on the disc as a series of light and dark pits; the light portion refers to the spaces between the pits. A laser beam reads the pits and the data can be accessed.

2. CD-R:

CD-R: Recordable Compact Discs, CD-Rs, are injection molded with a "blank" data spiral. A photosensitive dye is then applied, after which the discs are metalized and lacquer-coated. The write laser of the CD recorder changes the color of the dye to allow the read laser of a standard CD player to see the data, just as it would with a standard stamped disc. The resulting discs can be read by most CD-ROM drives and played in most audio CD players.

3. CD-RW:

CD-RW is a re-recordable medium that uses a metallic alloy instead of a dye. The write laser in this case is used to heat and alter the properties (amorphous vs. crystalline) of the alloy, and hence change its reflectivity. A CD-RW does not have as great a difference in reflectivity as a pressed CD or a CD-R, and so many earlier CD audio players cannot read CD-RW discs, although most later CD audio players and stand-alone DVD players can. CD-RWs follow the Orange Book standard.

4. DVD-ROM:

DVD-ROM: is an abbreviation of Digital Versatile Disc- read only memory. DVD-ROM is an optical disc storage media format that can be used for data storage, which includes movies with high video and sound quality. DVD-ROM is a non-volatile optical storage medium similar to CD-ROM, which contains computer data that cannot be erased or rewritten. These DVDs are read-only disks that have storage capacity for 133 minutes of high quality video, in format, and audio full- length feature film. The discs are pressed in a similar fashion as the CDs. The reflective surface is gold or silver colored.
DVD-ROM can be accessed using a DVD-ROM drive attached to the personal computer. DVD-ROM drives are backward compatible, i.e. they are also capable of reading CD-ROMs and audio CDs as well. The DVD-ROM supports disks with capacities of 4.7 GB to 17 GB and access rates of 600 KBps to 1.3 MBps. A standard DVD disc store up to 9.4 GB of data. DVD-ROMs are of same size as a compact disc, but holds data about 7 times more. DVD can store that much of data because both the sides of a disc are used, with sophisticated data compression technologies.

5. DVD-RW:

DVD-RW: stands for Digital Versatile Disk-Rewritable. It is a re-recordable optical disc, which can record up to 4.7 GB per side in a similar fashion to a CD-RW. DVD-RW supports sequential read/write access i.e. the device may need to wait for the correct location in a constantly revolving medium. The information stored on DVD-RW can be erased and rerecorded over multiple times without damaging the medium.
DVD-RW can be played in many DVD drives and players. Depending on quality, recording time varies from 1 hour to 6 hours.

6. Magneto Optical Drive

A magneto-optical drive is a kind of optical disc drive capable of writing and rewriting data upon a magneto-optical disc. Both 130 mm (5.25 in) and 90 mm (3.5 in) form factors exist. The technology was introduced commercially in 1985. Although optical, they appear as hard disk drives to the operating system and do not require a special filesystem; they can be formatted as FAT, HPFS, NTFS, etc. Magneto optical drives are common in some countries such as Japan but have fallen into disuse in other countries like the United States.