Optical disk are removable disk on which data is written and real using laser technology.

By new optical disk technology is well known to much people. an optical disk is a removable disk on which is a data is written and read thought the use of laser beams, the most familiar form of optical disk is the one used in the one used in the music industry. A compact disk, or CD, is an audio disk using digital code that is like a miniature phonograph record. A CD holds up to 72 minutes of high fidelity stereo sound.  Four types of optical disk are CD-ROM disk, CD-R disks, worm disks, and erasable optical disk. CD- ROM formats may be interactive and multimedia. variants of CD –room are CD-I, CDTV, and MPC.
Optical disk are removable disk

The optical disk technology that has revolutionized that music business with music CDs is doing the same for secondary storage with computers. a single optical disk of the tape called CD hold 650 megabytes of data. This works out to 250000 pages of text, or more than 7000 photos or graphics, or 19 hours of speech, or 72 minutes of video. Although some disk are used strictly for digital data storage, many combine text, visuals, and sound.

In the principal types of optical disk technology, a high-power laser beam is used to represent data by burning tiny pits into the surface of a hard plastic disk. To read the data a low powered laser light scans the disk surface pitted areas are not reflected and are interpreted as 0 bits smith areas are reflected and are interpreted as 1 bits. Because the pits are so tiny, a great deal more data can be represented that is possible in the same amount of space on a magnetic disk, whether floppy or hard.

 The optical disk technology used with computers consists of four types:




We will also describe some variations on these, such as video CDs, which offer the prospect of putting movies on CD-ROM disks.                                                   
 Disk format that is used to hold prerecorded text, graphics, and sound. 

Like music CD-ROM is a read only disk. read only means the disk cannot be written on or erased by the user. You as the user have access only to the data imprinted by the disk’s manufacturer. more and more microcomputers are being made with built in CD –ROM       drives however, many microcomputer users buy there CD –ROM dives separately and connect them to their computers. This requires installation of an audio circuit board and speakers if you wish to be able to play the kind of CD-ROM disks that offer music and sound.

Whereas at one time a CD-ROM drive was only a single speed drive, now there are double triple and even quadruple-speed drives. A single –speed drive will access data at 150 kilobytes per second, a double speed drive at 300 kilobytes per second. This means that a double-speed drive spins the compact disk twice as fast. The faster the drive spins, the more quickly it can deliver data to the processor. Some truly fast CD-ROM drives (such as the NEC multipoint 4x pro) will access data at 600 kilobytes per second.

At present, CD-ROMs are a standard 120 millimeters in diameter, which is considered a bit bulky to fit in mist notebook and handheld personal computers several companies, including Panasonic and Kodak, are supporting a new type of CD-ROM drive that will use a smaller size –80 millimeters. This size would have only one –third the capacity of regular CD-ROM disks but would play on standard CD-ROM drives, using an adapter ring.

Clearly CD-ROM has become an important medium. Among the uses are the following.  

Data storage: originally, computer makers thought that CD-ROM ‘’ would be good for storing databases, documents, directories, and other archival information that would not need to be altered said one report. customers would be libraries and business.

The principal CD-ROM encyclopedias are the Grolier multimedia encyclopedia, Compton’s new century encyclopedia and Microsoft’s Encarta. Each packs the entire text of a traditional multivolume encyclopedia onto a single disk, accompanied by pictures, maps, animation, and snippets of audio and video.

Catalogs: publishers have also discovered that CD-ROMs can be used as electronic catalogs, or even ‘’mega logs. ’’ One, for instance, combines the catalogs of several companies. ” A single disk now holds the equivalent of 7000 pages of information on almost 50000 different products from salad-bar sneeze-guards to deep-far fryers, ’’ noted one report. Cinemania offers a multimedia catalog of movies available on videotape.

Games: as you might expect, CD-ROM has been a hugely successful medium for games. Early bestsellers on the CD-ROM hit parade included 7th guest, battle chess and king quest v. the CD-ROM program called Sherlock Holmes. Consulting detective features three different murder mysteries to choose from. Each offers you the opportunity, with a Shakespearean actor playing Sherlock Holmes, to solve a murder with as few clues as possible.

Edutainment: edutainment software consists of programs that look like games but actually teach in a way that feels like fun. An example for children aged 3-6 is yearn 2 learn peanuts, which teaches math, geograment program for adults, plays the four movements of the symphony while the on-screen text provides a running commentary and allows you to stop and interact with the program.

Magazines and books: several magazines, including newspaper and business week, are publishing multimedia issues. Book publishers have produced several CD-ROM titles, including time-life 35mm photography and from alice to ocean, about a young woman’s 1700-mile trip by camel through the Australian outback.

Movies: as we describe shortly, using CD-ROMs for movies has some limitations. Nevertheless, you can watch films ranging from the 1954 white Christmas with bing Crosby to tom cruise’s top gun on home video CD.

One company has taken a movie called the discoverers, which okays on a giant five-story-high IMAX screen at Chicago’s museum of science and industry, and put it on CD-ROM. The disk uses the hypertext technique of the hot link to enable viewers to click on a word or picture and jump to related material.

Some companies are using CD-ROM jukebox as a means of increasing archive strong capacity. Based on the same principles as coin-operated music jukeboxes. CD-ROM jukeboxes can hold as few as six CDs and a single drive to as many as 1400 CDs and 32 drives.

About up to 100 color photographs and take them to a local photo shop for processing. A week later you will receive back not only conventional negatives and snapshots but also the images on a CD-ROM disk. depending on your equipment, you can then view the disk using any compatible CD-ROM drive. The drive could be for an IBM PC or macintosh, a CD-D device (described shortly), OR one of kodak’s own photo CD players, which have on the manipulation of photographs. With the right software, you can flip, crop, and rotate photos, incorporate them into desktop-publishing materials, and print them out on laser printers. Commercial photographers and graphics professionals can manipulate images at the level of pixels. Pixels, or picture element, are the dots of color that make up a picture. For example, they can easily merge images from different sources, such as superimposing the heads of show-business figures in the places of the U. S. presidents on mount rush-more. because the image is digital says one writer it can be taken apart pixel by pixel and put back together in many ways. This helps photo professionals further their range, although at the same time it also presents a danger that photographs will be compromised in their credibility. 

Worm stands for write once, read many.
A worm disk can be written, or recorded, onto just once and then cannot be crashed; it can be read many times. Worm disks hold 122-6400 megabytes of data. WORM technology is useful for storing data that needs to remain unchanged such as that used for archival purposes.

An erasable optical disk allows users to erase data so that the disks can megabytes of data.
The most common type of erasable and rewritable optical disk is probably the magneto optical disk which uses aspects of both magnetic disk and optical disk technologies. Such disks are useful to people who need to save successive versions of large documents, handle enormous databases. Or work in multimedia production or desktop publishing. 

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