Optical Media Types

Since the fist release of the recordable CD many different formats of optical media have been released. Different companies producing different standards of optical media each trying to secure their product as the actual "standard". The release of the DVD confused the issue even more and recordable standards have still not been reached to this day as DVD-R DVD+R and DVD-RAM battle it out for supremacy. Add to all this we now have Blu-Ray, a completely new type of optical media which uses a shorter wavelength laser to read and produce disks. Blu-Ray also has different formats to choose from. All of these formats together don't only give major manufacturers a headache about the compatibility of their products (such as films on DVD for example) but also for the home user. Does my optical drive support all of these media types? what sort of blank media do I require in order to create disks on my home burner? Its noticeable in shops that people buying blank media have trouble knowing which sort is the right one for their equipment. Also people are un-aware of the differences between the media types, for example what is the difference between DVD-R and DVD+R?

Hopefully we can put some answers to these questions by going through the media types in the table below and explaining the different technologies and the main purpose for each one of them.

CD Media

Abbreviation	Full Version	Notes
CD-ROM	Compact Disc - Read Only Memory	This standard CD format is used by manufacturers to distribute data on a compact disc. CD-ROM's cannot have the data stored on them changed and further data cannot be written to. Audio CD's are not the same as CD-ROM in 1 single way and that is the way the data is stored onto the disc. The CD-ROM is a called a WORM format (Write Once Read Many)
CD-R	Compact Disc - Recordable	The CD-R is a variation of the CD-ROM format. CD-R is once again a WORM format but was designed to have data written to it on home CD writers. Unlike the CD-ROM the data written to a CD-R does not have to be completed in a single session. More data can be written as long as the disc is not "closed". The CD-R format is highly compatible with most stand-alone CD players and can be played almost anywhere a standard CD-ROM can be played.
CD-RW	Compact Disc - Re-Writable	CD-RW was the first optical media that allowed data to be written to and erased ready to be re-written to again and again. the CD-RW disc has a layer of phase change recording material, an alloy usually made from silver, indium, antimony and tellurium. When the CD-RW was released the new technology was only compatible with PC CD-RW drives. Since then more stand-alone CD players are capable of reading CD-RW discs but the format is not entirely supported. The main use for the CD-RW was to backup computer files or to use and edit documents on the move before the more common flash drive came into use.

Phase Change Technology - the use of phase change materials in optical media started with the CD-RW. a re-writable format required a material that could easily have its physical state changed and would hold that state until altered again. A recordable layer was added to the CD (see the CD-RW above for the alloy) that could have its surface changed by a laser. the laser inside a CD burner would be powerful enough to change the state of the material.

Each CD writer capable of reading CD-RW's has two lasers inside, the read laser and the more powerful write laser. The write laser would be able to send the material into an amorphous state, changing its reflect-ability attributes and so turning that bit of the CD into an on or off state, basic binary system. The read laser would then be able to determine what data is written on the CD. The read Laser of course is not powerful enough to alter the state of the recording layer so as not to destroy the data.

In order to erase data on a CD-RW the write laser is set to a different pulse level reversing the changes made to the disc. while nothing actually touches the disc with phase change technology, there is still a limit on how many times this can be done to a single disc. Its common that on most CD-RW's that the limit is around 1000 changes before the disc starts to wear down and starts to fail to retain data.

Next - DVD Media