| OPTICAL DISK | | | | correction and detection. |
| Optical disk is an electronic data storage medium | | | | Mode-1 CD-ROM: It has full three layers of error |
| from which data is read and written to by using a | | | | correction data, which contains 2048 bytes of the |
| low-powered laser beam. It is flat, circular, plastic or | | | | available 2352 per sector. |
| glass disk on which data is stored in the form of light | | | | Mode-2 CD-ROM: It is mostly used for video files, |
| and dark pits. The laser beam reads the pits and the | | | | which contains 2336 user-available bytes per sector. |
| data can be accessed. There are three basic types | | | | CD-ROM SPEEDS AND USES |
| of optical disks:o Read-only optical disks: The optical | | | | + Early CD-ROM drives were known as single-speed |
| disks, which are recorded at the time of manufacture | | | | and could read the data at the speed of 150 KBps. |
| and cannot be erased. CD, CD-ROM, DVD-ROM, and | | | | + CD-ROM drives can transfer data up to the speed |
| DVD-Video are the read-only disks.o WORM: WORM | | | | of 7800 KBps |
| stands for write-once, read many. The optical disks | | | | + CD-ROM can store audio, video, text and program |
| that can be recorded by the user only once but | | | | instructions. It is used to store software programs. |
| cannot be erased. After they have been recorded | | | | DVD-ROM |
| once, they behave like a read-only optical disk CD-R, | | | | DVD-ROM: is an abbreviation of Digital Versatile Disc- |
| DVD-R, and WORM disks are write-once.o Rewritable | | | | read only memory. DVD-ROM is an optical disc |
| Magneto-optic disks: The optical disks that can be | | | | storage media format that can be used for data |
| erased and written to with the new information. | | | | storage, which includes movies with high video and |
| CR-RW, DVD-RAM, DVD-RW, and magneto-optic | | | | sound quality. DVD-ROM is a non-volatile optical |
| disks and Data play are rewritable. Rewritable disks | | | | storage medium similar to CD-ROM, which contains |
| use magneto-optic or phase change technology. | | | | computer data that cannot be erased or rewritten. |
| An optical disk offers many advantages over | | | | These DVDs are read-only disks that have storage |
| magnetic storage media.o Highest storage capacityo | | | | capacity for 133 minutes of high quality video, in |
| Low cost per Megabyte of storageo Environmental | | | | format, and audio full- length feature film. The discs |
| condition toleranceo High data stabilityo Long media | | | | are pressed in a similar fashion as the CDs. The |
| life | | | | reflective surface is gold or silver colored. |
| An optical disk has much more storage capacity on | | | | DVD-ROM can be accessed using a DVD-ROM drive |
| the order of gigabytes, than a magnetic disk. It can | | | | attached to the personal computer. DVD-ROM drives |
| hold up to 6GB of data in comparison to 1.44 MB of a | | | | are backward compatible, i.e. they are also capable of |
| diskette. Optical disks are inexpensive to | | | | reading CD-ROMs and audio CDs as well. The |
| manufacture. Data stored on optical disks is resistant | | | | DVD-ROM supports disks with capacities of 4.7 GB to |
| to power surges or magnetic disturbances, such as | | | | 17 GB and access rates of 600 KBps to 1.3 MBps. A |
| head crashes or corruption form stray magnetic | | | | standard DVD disc store up to 9.4 GB of data. |
| fields. Hence, they provide high data stability. Optical | | | | DVD-ROMs are of same size as a compact disc, but |
| disks are less vulnerable to extremes of hot and cold | | | | holds data about 7 times more. DVD can store that |
| ascompared to the magnetic disks. Optical disks have | | | | much of data because both the sides of a disc are |
| long media life than magnetic disks. | | | | used, with sophisticated data compression |
| OPTICAL STORAGE DEVICES | | | | technologies. |
| CD-ROM | | | | DVD-ROM is a variation of CD-ROM that is being |
| CD-ROM: is an abbreviation of Compact Disc | | | | used in place of CD-ROMs in many personal |
| Read-Only Memory. A CD-ROM is a CD that contains | | | | computers. All DVD-ROMs contain a file system, UDF, |
| computer data, which cannot be read or rewritten. | | | | which is an extension of the ISO 9660 Standard used |
| Incomputers, CDROM is the most commonly used | | | | for data CDs. |
| optical storage technology. CD-ROM is a compact disc | | | | CD-RW |
| that contains information, which is accessible by a | | | | CD-RW is an abbreviation of compact disc-rewritable. |
| computer. It is composed of polycarbonate plastic, | | | | It is a recordable CD format that can be erased and |
| thin reflective metal layers, made of aluminium and a | | | | rerecorded multiple times, just like a floppy disk or a |
| lacquer coating. Data is stored on the disc as a series | | | | hard disk. It is a rewritable version of CD-ROM. |
| of light and dark pits; the light portion refers to the | | | | CD-RW disc is round plastic, about 5 inches in |
| spaces between the pits. A laser beam reads the pits | | | | diameter. CD-RW disks can be played or recorded in |
| and the data can be accessed. | | | | the CD-RW drive only. These disks behave unusable |
| CD-ROM is an adaptation/EXTENSION of the | | | | when put in a regular CD-drive or a CD-R drive |
| compact disc that is designed for music storage and | | | | cannot be played. A CD-RW drive can read |
| playback. The format of CD-ROM is very similar to an | | | | everything except a DVD. |
| audio CD; the only difference being the standards | | | | A CD-RW can hold 650 Megabytes of data (unlimited |
| used to store data. A standard 120 mm CD-ROM | | | | number of times) written by a CD-RW drive. CD-RW |
| holds up to 700 MB of data, or about 70 minutes of | | | | cannot be selectively overwritten but can be |
| audio. This may mean that One CD can contain over | | | | extended. CD-RWs must be closed before they can |
| one thousand novels; an average novel being | | | | be read in a normal CD-ROM drive. CD-RW disks |
| composed of 60, 000 words. Once the data is | | | | cannot be read using a CD-ROM drive built before |
| written to a standard CD-ROM disc, it cannot be | | | | 1997. CD-RWs can be randomly read and written |
| altered or rewritten. | | | | because of the variation of UDF format. CD-RW |
| A CD-ROM can be read using a CD-ROM drive, which | | | | disks and drives are more expensive than a regular |
| is almost common on the personal computers. A | | | | CD-ROM drive or media. A CD-RW disc can be read |
| CD-ROM drive may be connected to the computer in | | | | optically by laser light. |
| several different ways depending on the type of | | | | DVD-RW |
| interface, such as:o IDE (ATA)o SCSIo SATAo | | | | DVD-RW: stands for Digital Versatile Disk-Rewritable. |
| Firewireo USB | | | | It is a re-recordable optical disc, which can record up |
| Almost all modern CD-ROM drives can play audio as | | | | to 4.7 GB per side in a similar fashion to a CD-RW. |
| well as video CDs. | | | | DVD-RW supports sequential read/write access i.e. |
| CD-ROM STANDARDS | | | | the device may need to wait for the correct location |
| CD-ROM format provides an outstanding solution to | | | | in a constantly revolving medium. The information |
| the problem of storing large digital files. Several | | | | stored on DVD-RW can be erased and rerecorded |
| formats are used for data stored on CD-ROMs. | | | | over multiple times without damaging the medium. |
| These include Red book standards for audio-CD, | | | | DVD-RW is a phase-change erasable format based |
| White Book and Yellow Book for CD-ROM. An ISO | | | | on DVD-R, using similar mark length, track pitch and |
| 9960, which defines the standard file system of a | | | | rotation control. The format is supported by the DVD |
| CD-ROM is due to be replaced by ISO 13490. | | | | Forum. DVD-RW is also called "DVD Dash RW" and |
| CD-ROM FORMAT | | | | "DVD Minus RW". |
| One CD-ROM sector contains 2352 bytes, which is | | | | DVD-RW can be played in many DVD drives and |
| further divided into 98 24-byte frames. A CD-ROM | | | | players. Depending on quality, recording time varies |
| contains a third layer of Reed-Solomon error | | | | from 1 hour to 6 hours. |
| correction in order to achieve improved error | | | | |