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

An optical disk has much more storage capacity on the order of gigabytes, than a magnetic disk. It can hold up to 6GB of data in comparison to 1.44 MB of a diskette. Optical disks are inexpensive to manufacture. Data stored on optical disks is resistant to power surges or magnetic disturbances, such as head crashes or corruption form stray magnetic fields. Hence, they provide high data stability. Optical disks are less vulnerable to extremes of hot and cold as
compared to the magnetic disks. Optical disks have long media life than magnetic disks.

OPTICAL STORAGE DEVICES

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 read or 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 aluminium 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.

CD-ROM is an adaptation/EXTENSION of the compact disc that is designed for music storage and playback. The format of CD-ROM is very similar to an audio CD; the only difference being the standards used to store data. A standard 120 mm CD-ROM holds up to 700 MB of data, or about 70 minutes of audio. This may mean that One CD can contain over one thousand novels; an average novel being composed of 60, 000 words. Once the data is written to a standard CD-ROM disc, it cannot be altered or rewritten.

A CD-ROM can be read using a CD-ROM drive, which is almost common on the personal computers. A CD-ROM drive may be connected to the computer in several different ways depending on the type of interface, such as:

• IDE (ATA)

• SCSI

• SATA

• Firewire

• USB

Almost all modern CD-ROM drives can play audio as well as video CDs.

CD-ROM STANDARDS

CD-ROM format provides an outstanding solution to the problem of storing large digital files. Several formats are used for data stored on CD-ROMs. These include Red book standards for audio-CD, White Book and Yellow Book for CD-ROM. An ISO 9960, which defines the standard file system of a CD-ROM is due to be replaced by ISO 13490.

CD-ROM FORMAT

One CD-ROM sector contains 2352 bytes, which is further divided into 98 24-byte frames. A CD-ROM contains a third layer of Reed-Solomon error correction in order to achieve improved error correction and detection.

Mode-1 CD-ROM: It has full three layers of error correction data, which contains 2048 bytes of the available 2352 per sector.
Mode-2 CD-ROM: It is mostly used for video files, which contains 2336 user-available bytes per sector.

CD-ROM SPEEDS AND USES

+ Early CD-ROM drives were known as single-speed and could read the data at the speed of 150 KBps.

+ CD-ROM drives can transfer data up to the speed of 7800 KBps

+ CD-ROM can store audio, video, text and program instructions. It is used to store software programs.

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.

DVD-ROM is a variation of CD-ROM that is being used in place of CD-ROMs in many personal computers. All DVD-ROMs contain a file system, UDF, which is an extension of the ISO 9660 Standard used for data CDs.

CD-RW

CD-RW is an abbreviation of compact disc-rewritable. It is a recordable CD format that can be erased and rerecorded multiple times, just like a floppy disk or a hard disk. It is a rewritable version of CD-ROM. CD-RW disc is round plastic, about 5 inches in diameter. CD-RW disks can be played or recorded in the CD-RW drive only. These disks behave unusable when put in a regular CD-drive or a CD-R drive cannot be played. A CD-RW drive can read everything except a DVD.

A CD-RW can hold 650 Megabytes of data (unlimited number of times) written by a CD-RW drive. CD-RW cannot be selectively overwritten but can be extended. CD-RWs must be closed before they can be read in a normal CD-ROM drive. CD-RW disks cannot be read using a CD-ROM drive built before 1997. CD-RWs can be randomly read and written because of the variation of UDF format. CD-RW disks and drives are more expensive than a regular CD-ROM drive or media. A CD-RW disc can be read optically by laser light.

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 is a phase-change erasable format based on DVD-R, using similar mark length, track pitch and rotation control. The format is supported by the DVD Forum. DVD-RW is also called “DVD Dash RW” and “DVD Minus RW”.

DVD-RW can be played in many DVD drives and players. Depending on quality, recording time varies from 1 hour to 6 hours.

Digital storage devices allows you to store and retrieve data if you need. They are compatible with most electronic products. Many consumers prefer digital storage because of their small size, storage and portability. There are many types of digital storage devices on the market. It’s always good to think about what type of digital storage device is compatible with your electronics before choosing one.

How does a memory data storage?

An electronic memory functions and uses Flash memory, Flash memory, data storage on the non-volatile memory chips. Memory-cards have the ability, power, delete or reschedule all data recorded.

What are the different types of storage devices available on the market?

Compact Flash (CF):

Compact Flash is the size of a box of matches and is used in a variety of electronic devices, including PDAs, digital cameras, Digital Voice Recorder and set-top TV boxes. There are two models: Type I and Type II is thicker and offers an expandable memory option. Type I cards often adapt by default in a laptop with location using a map cheap and are also compatible with Compact Flash Type II slots. Compact Flash cards can be used in a PCMCIA slot, if you use an adapter. Otherwise, you need a device with a Compact Flash Type I housing.

Smart Media (SM):

The Smart Media is often regarded as maps SSFDC (Solid-State Digital Flash Cards). They are as thin as credit cards and the size of a box of matches. They are specially adapted for digital devices like digital cameras, MP3 player, PDA, etc.. Smart Media storage capacities up to 128 megabytes. Some devices have slots for Smart Media and Compact Flash cards. If this is not the case, you need a Smart Media Slot, a SmartMedia card.

MultiMedia Card (MMC):

The MMC is a postage stamp-size card in mobile phones, pagers, video cameras, global positioning systems, laptops, MP3 players and PDAs. Your storage capacity ranging from 256 MB to 4 GB Devices, Secure Digital cards, MultiMedia cards also.

Secure Digital (SD):

The Secure Digital memory card is successful, the MMC. It is a little thicker than the MMC, additional storage capacity and a digital copyright of security, copyright protection for data. The digital storage medium is very popular with many PDA, organizer, mobile phone and MP3 player. Devices that use MultiMedia Cards may also accept Secure Digital cards.

Memory Stick:

The Memory Stick is a storage device developed exclusively by Sony. It is compatible with most Sony products, like digital cameras, laptops, MP3 players and PDAs. They have a storage capacity of 256 MB to 8 GB, and supports USB 1.1 and 2.0 for better accessibility. This is a special version of the Memory Stick with Digital Rights Management functions for some devices. This card is issued by one of the following names – Magic Gate Memory Stick, MagicGate Memory Stick Duo media or Memory Stick PRO Duo Media. Users can and transporting data to your computer USB port using the Micro Vault USB storage.

xD-Picture Card:

Map xD-Picture Card is the smallest storage format for recording, storing and transporting audio-visual information. In addition, the xD-Picture Card is designed to save energy and prolong the life of the battery of your digital. You can use the xD cards in a Compact Flash, if you use an adapter. Some devices have card slots for xD and SmartMedia cards. If the device is not on the two connectors, one device with an xD-card housing is provided with a card xD-Picture Card.

What are memory card readers and card?

Memory Card, a memory card to maximize performance by increasing transfer speed of up to 60 MB / sec In addition to the potential for expansion, memory cards, card on the data transmission capacity without the device to the computer with a cable. The card reader read most memory cards such as SD card, CF Card, MMC, and many series. Most readers of performance and writing, so it may Pen Drive.

What are the most popular brands?

Memory of the digital camera manufacturers, like Sony and Olympus, have usually very popular with consumers. If you’re concerned about the speed of the memory of your digital camera, for brands such as Lexar, SanDisk and Simple Tech. Lexar High-Speed Card, Simple Tech Prox cards and SanDisk Ultra cards have speeds much higher than most memory cards.

What are the instructions for using a memory card?

Removing a memory card of a device, while data is processed. It is recommended to switch off the device before removing the operating system to a memory card. In addition, you must have a memory card in any device with low battery. Do not touch the metal connectors of the memory card, especially cards Secure Digital, SmartMedia and xD to discharge static electricity data.