Types of Compact Discs

By Peggy Epstein

In 2002 the American Computer Museum honored James Russell as the inventor of the digital compact disc; Russell actually holds twenty-two patents on the compact disc he invented in 1965. In 1979 Phillips and Sony collaborated developing the digital audio disc and by 1982 the first CD recording, "The Visitors" by ABBA, was recorded. All compact discs store the data in pits on a thin film of aluminum over a plastic disc that is 1.2 mm thick. There are several different kinds of compact discs, but they all do the same thing: store digital information.


The term ROM means "read only memory" and describes all prerecorded CD's that contain music. A recording of the music is burned into the CD by the vendor and cannot be erased or changed. CD ROM recordings can be played on any standard CD player, and contain 650 megabytes of storage, about the amount contained in 700 floppy disks.


The Mini CD is only 80 mm, or about three inches, wide and holds a maximum of 24 minutes of music or 210 megabytes of data. Mini CD's are compatible with most CD players. The depression that a normal size CD fits into also has a smaller well in the middle of it that will hold a Mini CD. The most common use for the mini format is for single song recordings, but they are also used by businesses for advertising purposes.


The "R" in CD-R stands for recordable. The CD-R allows the user to record data or music only once. Some CD-R's hold as much as 80 minutes of music, but 74 minutes is the usual amount of music storage available. CD-R can be used to store a wide variety of digital data in much the same way that data was stored on a floppy disk. The data does not become a permanent part of the disc until it is burned in by a CD burner, which is included in most computers.


Although the "R" in CD+R stands for recordable, a CD+R disc is not compatible with a CD-R. The +R format was developed by a group of companies to increase the amount of storage available on a compact disc. The double layer technology in a CD+R allows for almost twice as much storage space as a standard CD-R.


The CD-RW can be used as a normal CD-R, but it can also be erased and re-used. A CD burner will use its highest laser power to melt the recording layer to record data onto a CD. The CD-RW burner uses its medium level of laser power to melt the data layer so new data can be added to the disk. To read a CD, a CD player uses the lowest amount of laser power and will not change the recorded layer.