Optical media are types of storage media that hold content in digital form and that are written and read by a laser.
There are many different types of optical discs, from CDs to DVDs, and each has a unique set of pros and cons.
When recommending optical media to your customers, you need to take into account the writable standard they support, the dyes and other materials they use, their compatibility with different models of writers and players, their archival stability and their overall quality.
The original compact disc (CD) specification still stands today. Optical media discs are 120mm in diameter, have a 60mm radius and are 1,2mm thick. They have a standardised central hole which accommodates the rotating central spindle of the optical drive.
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CDs and DVDs are produced using a physical stamping process, and are called pressed discs or stamped discs. Commercial discs may be one-sided or two-sided, with data sides being a reflective silver colour. Writable discs are produced by a high-powered laser on a layer of dye that can be altered by light. These are always one-sided, with the data side being silver, gold or dark blue.
Discs differ in terms of the quality of the materials used to make them, and it is worth informing your customers that buying cheaper discs may lead to issues with the archival stability and the quality of the reflective layer. Cheap discs may stop working sooner, and their data will be lost.
Despite their similarity in appearance, there are many different types of discs.
CD writers themselves may no longer exist, but CDs are still a good buy for your customers. Even premium brands are affordable, and can be found in large quantities. Speak to your customers and ask what they plan to do with their optical discs. CDs are great for duplicating audio CDs and making quick backups of data.
There are two types of writable CDs:
CD-R (CD-Recordable) discs can usually only be written to once. This means that any data recorded on the CD cannot be overwritten or deleted.
Most CDs 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.
In general, CD-R discs differ in capacity and quality. Standard CD-R discs store 74 minutes of audio (650Mb of data), but there are also 700Mb (80 minutes of audio) discs available.
CD-RW (CD-Rewritable) discs can be written to repeatedly. Data is deleted or overwritten 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 discs. Writers often refuse to burn CD-RW discs at anything faster than the speed indicated on the front of the disc.
Although most recent optical drives and players can read CD-RW discs, there were many early compatibility problems, and so this is an underutilised type of media.
There are significant quality variations between brands of CD-RW discs.
Did you know?
A writable DVD said to have a capacity of 4,7Gb actually stores 4 700 000 000 bytes. Contrary to popular belief, the units of measurement of data storage are not in round thousands, but are actually in units of 1 024. For example, one megabyte contains 1 024 kilobytes, not 1 000 kilobytes. Thus a DVD of 4,7Gb actually only has 4,4Gb of capacity.
Unlike writable CDs, for which only the CD-R and CD-RW standards exist, there are numerous standards for writable DVDs. And unlike CDs, rewritable standards for DVDs preceded write-once standards. DVDs are ideal for customers who want to store large amounts of data, such as music, photographs or videos.
Early DVD-RW has 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. They can be rewritten up to 1 000 times and can store about 4,7Gb worth of information.
Because DVD-RW has relatively poor error detection and correction, these discs are poorly suited for recording data. However, DVD-RW discs are less expensive than comparable DVD+RW discs, and so are a reasonable choice for recording television programs, movies and other noncritical types of data.
DVD-RW 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. Estimates vary, but approximately 65% to 70% of all installed DVD players play DVD-RW discs correctly.
The greatest advantage of DVD+RW discs is that they have much better performance and reliability.
DVD+RW discs store about 4,7Gb and are rated for 1 000 rewrites. They are not only faster than DVD-RW, but have superior error detection and correction.
DVD+RW 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. Approximately 70% to 80% of all installed DVD players play DVD+RW discs correctly.
Advise your customers to use DVD+RW discs when backing up important data.
DVD-R was the first write-once DVD format introduced. These discs store about 4,7Gb in size, and are available at up to 16X write speeds. However, error detection and correction is poor, and so it is best to advise your customers not to use these types of discs for storing important data.
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.
DVD+R is a superior alternative to DVD-R. These discs store about 4,7Gb of data and can write up to 16X. Error detection and correction on these discs is much higher, and is therefore a good choice for storing data.
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%).
The most recent enhancement to the DVD+R standard is DVD+R DL. The DL stands for dual-layer, and these discs have a storage capacity almost double that of DVD+R discs (8,5Gb).
These discs are most costly than their single-layer counterparts. Even so, they are ideal for customers that wish to back up larger amounts of data. They are also useful for backing up original DVD movies. The higher capacity of DVD+R DL allows video to be duplicated without the compression required to fit on a single-layer discs.
DVD+R DL compatibility with drives and players other than DVD+R DL writers is problematic.
If your customer wants to use DVD+R DL discs, recommend that they first verify compatibility with their current DVD drives and players.
DVD-R DL (also called DVD-R9 or dual-layer DVD-R) has a number of drawbacks. It has the same compatibility issues as DVD+R DL, in addition to error detection and correction that’s inferior to the plus-format version.
DVD-R DL is acceptable for recording video, but the superior reliability and features of DVD+R DL make the plus versions a better choice for your customers.
Blu-ray discs are a next-generation optical disc format that offers more than five times the storage capacity of traditional DVDs. It can store up to 25Gb on a single-layer disc, and 50Gb on a dual-layer disc. Blu-ray discs are exactly the same physical size as CDs and DVDs.
Blu-ray discs are made by using a blue laser with a shorter wavelength of 405nm. DVDs use a 650nm wavelength red laser, while CDs use a 780nm red laser.
The shorter wavelength of the Blu-ray system allows the laser to focus on smaller spots. This means the pits and spiral groove in the discs can be made even smaller and tighter.
Blu-ray discs are ideal for the recording, rewriting and playback of high-definition (HD) video, as well as for storing large amounts of data.