What is optical Disk? How many types of optical disk? Explain them briefly.
|Subject||Peripheral and Interfacing|
|NU Year||Set: 4.(c) Marks: 1+5=6 Year: 2017|
An optical disk is any computer disk that uses optical storage techniques and technology to read and write data. It is a computer storage disk that stores data digitally and uses laser beams (transmitted from a laser head mounted on an optical disk drive) to read and write data.
Optical Disc Types
All mainstream optical discs, from the oldest CDs to the most recent high-capacity DVDs, are based on the original CD specification. The dimensions of a standard CD or DVD are 120 mm in diameter (60 mm radius) by 1.2 mm thick, with a 15 mm diameter central hole that accommodates the rotating center spindle of the drive.
Commercial CDs and DVDs are produced by a physical stamping process, and are referred to as pressed discs or stamped discs. Commercial discs may be one-sided or two-sided, and the data side or sides are nearly always a reflective silver color. Writable discs are produced by the operation of a relatively high power laser on a layer of dye or another substance that can be altered by light, and are always one-sided. The data side of a writable disc may be nearly any color, from a metallic silver or gold to yellow-green to a dark blue. It is not possible to identify the type or quality of a writable disc by visually examining its data side.
Despite their similarity in appearance, there are many differences between discs. Discs vary in the writable standard they support, the dyes and other materials they use, compatibility with different models of writers and players, archival stability, and overall quality.
Writable CD discs
Although CD writers are obsolescent, writable CD discs continue to sell by the billions. Writable CDs are cheap even premium brands can be bought in bulk for as little as $0.10 each when they're on sale and are ideal for duplicating audio CDs, making quick backups of your working data, and other tasks for which their capacity is sufficient. Writable CDs can be written to by CD writers (of course), and by most DVD writers. There are two types of writable CDs:
CD-R (CD-Recordable) discs can, with minor exceptions, be written to only once. Data, once recorded, cannot be overwritten or deleted. Although CD-R discs formerly differed in the maximum write speeds they supported, nearly all CD-R discs currently sold are rated for 48X to 52X writes, and so can be used in nearly any optical writer. CD-R discs can be written by all CD writers and by nearly all DVD writers. CD-R discs can be read by any modern optical drive or player, although some elderly home audio and automobile CD players reject them.
CD-R discs differ primarily in capacity and quality. A standards-compliant CD-R disc stores 74 minutes of audio or about 650 MB of data. Although they are nonstandard, most CD-Rs now sold have a capacity of about 80 minutes of audio or 700 MB of data. In fact, for the same reason 74-minute discs drove 63-minute discs out of the market, it's almost impossible nowadays to find 74-minute discs.
CD-RW(CD-Rewritable) discs can be written to repeatedly, by deleting or overwriting old data to make room for new data. CD-RW discs can be rewritten up to 1,000 times.
Rated disc speed is more important for CD-RW than for CD-R. While most writers happily burn (or attempt to burn) any CD-R disc at the highest CD-R speed the drive supports, many writers refuse to burn CD-RW discs at anything faster than the disc's rated speed. There are four types of CD-RW media currently available:
- Standard Speed CD-RW discs are rated for 1X to 4X burning, and are usable only in elderly CD-RW writers.
- High Speed CD-RW discs are rated for 4X to 12X burning, and are usable in CD-RW writers with the High Speed CD-RW logo or Ultra Speed CD-RW logo.
- Ultra Speed CD-RW discs are rated for 12X, 16X, and 24X burning, and are usable in CD-RW writers with the High Speed CD-RW logo or Ultra Speed CD-RW logo.
- Ultra Speed+ CD-RW discs are rated for 32X burning, and are usable in CD-RW writers with the High Speed CD-RW logo or Ultra Speed CD-RW logo.
CD-RW discs were always the poor stepchild, and are now much less widely available than CD-R discs, which remain commonplace. Although nearly any recent optical drive and most recent CD and DVD players can read CD-RW discs, there were many early compatibility problems that caused many people to write off CD-RW as a viable technology. At the time CD-RW began to achieve critical mass, many CD-ROM and DVD-ROM drives and most home audio and automobile CD players of the time refused to read CD-RW discs.
As is true of CD-R discs, there are significant quality variations between brands of CD-RW discs. Standard Speed and Ultra Speed+ discs are now difficult to find, and we have no brand recommendations for them. For High Speed CD-RW discs (usually labeled 12X) and Ultra Speed CD-RW discs (usually labeled 24X), we recommend Verbatim.
Writable DVD discs
Unlike writable CDs, for which only the CD-R and CD-RW standards exist, there are numerous standards for writable DVD. This proliferation of writable DVD formats had its origin in the "format wars" that began in the late 1990s and continue even today. As a result, there are three mainstream standards for rewritable DVD discs, and four standards for write-once DVD discs. Interestingly, rewritable standards generally precede the corresponding write-once standards. Here are the primary rewritable standards:
DVD-RAM drives first shipped in 1998, beating all other writable DVD standards to market. The DVD Forum promoted DVD-RAM, initially for use primarily on PCs, although DVD-RAM later achieved some popularity for recording home video. Although it was first to market, DVD-RAM never really caught on. A combination of high drive prices, expensive media, and slow performance pretty much doomed DVD-RAM right out of the starting gate. It didn't help that the original DVD-RAM specification required discs to be enclosed in cartridges, which kept the price of DVD-RAM discs high and prevented DVD-RAM drives from being used in notebook computers. The one saving grace of DVD-RAM is that it incorporates much more robust error detection and correction than do other writable DVD formats, making DVD-RAM particularly appropriate for back ups and similar data-related tasks.
DVD-RAM drives are still made, and continue to sell in small numbers. DVD-RAM drives write at 5X, slower than other rewritable discs. DVD-RAM discs store 4.7 GB per side about half the capacity of dual-layer DVD R DL discs and are available in single-sided 4.7 GB versions and double-sided 9.4 GB versions. 4.7 GB discs are available bare or in a cartridge. 9.4 GB discs are available only in cartridges. DVD-RAM discs sell for 3 to 10 times the price of DVD+RW or DVD-RW discs, depending on their capacity and whether they are bare or contained in a cartridge. DVD-RAM discs, particularly cartridge-based discs, are compatible only with DVD-RAM drives, some camcorders and personal video recorders, a few DVD-ROM drives (primarily Toshiba models), and a very few DVD players. DVD-RAM discs can be rewritten up to 100,000 times.
DVD-RAM discs are much harder to find than DVD R/RW discs. You may find a limited selection at your local big-box store, although they're often not stocked, and even many online vendors do not carry DVD-RAM media. We prefer to use DVD-RAM discs made by Verbatim, Maxell, or TDK.
DVD-RW is another rewritable standard promoted by the DVD Forum. DVD-RW drives appeared on the market shortly after DVD-RAM drives, and quickly achieved moderate success. Apple adopted and promoted DVD-RW heavily, using drives built by Pioneer. Early 1X drives and discs were soon followed by 2X and then 4X models. Current DVD-RW discs are certified for 4X or (rarely) 6X writes, are rated for up to 1,000 rewrites, and store about 4.7 GB. DVD+RW
DVD-R was the first write-once DVD format introduced. DVD-R discs store about 4.7 GB, and are available in versions certified for up to 16X writes. As is true of DVD-RW discs, DVD-R discs have error detection and correction inferior to that of DVD+R/RW discs, so we avoid using DVD-R discs whenever possible, particularly for storing data (as opposed to video). If you own a minus-only recorder, have a DVD player that does not read plus formats, or for some other reason you must use DVD-R discs, we recommend those made by Maxell, TDK, or Verbatim.
DVD-R discs can be read by any DVD writer other than some elderly DVD+R/RW-only models, and by nearly all recent DVD-ROM drives. More than 90% of all installed DVD players play DVD-R discs correctly, and that percentage will increase as older players are replaced by new units. Some old DVD players are unable to deal with the lower contrast and reflectivity of DVD-R discs relative to pressed discs, but most of those players have long since been replaced.
After some false starts, DVD+R quickly established itself as a superior alternative to DVD-R. DVD+R discs, which store about 4.7 GB, are available in versions certified for up to 16X writes. DVD+R discs have better error detection and correction than DVD-R discs, and are therefore a better choice for recording data. We use and recommend DVD+R discs made by Maxell or Verbatim, both of which are excellent and well distributed. Ricoh, Taiyo-Yuden and Mitsubishi Chemical Company (MCC, the parent of Verbatim), also produce excellent DVD+R discs, although none of those brands is widely distributed in the U.S.
DVD+R discs can be read by any DVD writer other than some elderly DVD-R/RW-only models, and by nearly all recent DVD-ROM drives. A somewhat lower percentage of DVD players are compatible with DVD+R than DVD-R (perhaps 85%), because even some current DVD players are intentionally made incompatible with DVD+R/RW.
The most recent enhancement to the DVD+R standard is DVD+R DL (also called DVD+R9 or dual-layer DVD+R), which boosts storage capacity from 4.7 GB to 8.5 GB by adding a second recording layer. Although DVD+R DL compatible drives have been shipping since Summer 2004, initial acceptance of the format was limited because of the very high cost of DL discs. A full year after the introduction of DL drives and discs, name-brand DVD+R discs were readily available for $0.50 each or less, while DL discs sold for 6 to 10 times that price.
Nonetheless, DVD+R DL discs have their place. For backing up data, their higher price may be a small issue when their additional capacity is taken into account. Also, for those who back up their commercial DVD-Video discs, the higher capacity of DVD+R DL allows that video to be duplicated without the compression required to fit it onto 4.7 GB single-layer discs. Our experience with DVD+R DL discs is very limited, but of those we have used we have found Verbatim and TDK discs to be the most reliable.
DVD+R DL compatibility with drives and players other than DVD+R DL writers is problematic. Many recent DVD-ROM drives and DVD players can read DVD+R DL discs, but even some current models cannot. If you plan to use DVD+R DL, we recommend that you first verify compatibility with your other DVD drives and players.
DVD-R DL (also called DVD-R9 or dual-layer DVD-R) arrived on the scene some months after DVD+R DL. DVD-R DL has the same issues as DVD+R DL high disc cost and limited compatibility with older devices. DVD-R DL, like standard DVD-R, has error detection and correction that's inferior to the plus-format versions, so we regard DVD-R DL as unsuitable for recording data. Although DVD-R DL is acceptable for recording video, the superior reliability and features of DVD+R DL make it a better choice. We cannot recommend specific brands of DVD-R DL discs, because we have almost no hands-on experience with that format.