Optical storage media contains digital data that is written to and read by a laser.
Product categories include compact disks (CD) and digital video disks (DVD). Both types of optical disks contain a reflective layer, a data layer, and a polycarbonate substrate. Data is retrieved by shining a laser against the reflective layer. The data layer is either readable or both readable and writeable, and may be either metallic or die-based.
Another key difference between types of optical discs is the amount of storage space. DVDs can hold significantly greater amounts of data, but CDs can also be used to store digital video files. Optical storage media includes different types of compact discs. Each type of disk has a lettered designation. For example, CD-ROM disks use read-only memory (ROM) and are non-writable. CDs that are recordable (CD-R) can be burned with data only once unless multisession mode is used. The numbers that follow a CD-R disc indicates the device’s storage capacity in minutes. Choices include CD-R 74, CD-R 80, CD-R 90, and CD-R 99. Rewritable CDs (CD-RW) can be burned many times so that users can add, erase, and replace data repeatedly. With CD-RWs, the burning process requires special software. For compact disks, variants of the most common optical storage media technologies include CD-ROM XA (extended architecture) and CD-WO (write once). CD-ROM XA permits the more accurate synchronization of data, audio, and video formats on optical media. Form 1 of XA uses full error correction while Form 2 expands multimedia storage capabilities. CD-WO disks can be written to once, but neither erased nor re-written.
Typically, all types of CDs can be used with the CD-ROM drives of personal computers (PCs), notebooks, and laptops. Audio disks can be used with CD players. Digital video disks or digital versatile disks (DVD) are available in single or double layers (DL). Double-layer DVDs (DVD-DL) have twice as much memory. DVD-ROM disks are similar to CD-ROM disks in that both feature read-only memory; however, a standard DVD has six times more memory than a CD. DVD optical storage media also includes recordable or writeable disks designated as DVD-R or DVD+R. Similarly, a rewriteable DVD may be listed as DVD-RW or DVD+RW. For both types of optical storage media, the plus (+) and minus (-) signs indicate different the format. DVD-RAM disks with random access memory (RAM) are also available from suppliers of optical storage media.