Optical Storage: The Basics
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Optical storage might seem to be an odd term that mixes eyes with warehousing, but it's actually everywhere – the CDs that contain your favorite games and the DVDs that hold last year's Hollywood blockbusters are but two types of optical storage.
Optical storage deals with data storage and is usually considered as a type of tertiary storage. (Tertiary storage comes in the form of low-cost removable media, such as CD-ROMs and floppy disks, while secondary storage comes in the form of the hard disks found within your computer. However, some people like to put optical media in the same bunch as hard disks, and thus consider them as secondary memory.)
Optical storage differs from other types of storage media, such as magnetic storage (e.g. floppy disks, hard disks, magnetic tapes) and flash memory (which uses electrical charges). The different types of optical storage vary in material composition, technology, and storage capacity, but are mostly cheaper (cost per data bit -wise) than other types of storage, save only for magnetic tapes.
Optical storage technology is much, much more recent than other types of data storage, and optical media generally have higher recording densities. Take note, however, that the latter doesn't necessarily equate to higher storage capacity, as other types of storage (especially hard disks) can store larger amounts of data. Of course, one must consider the bulkiness of a hard disk compared to the slimness of optical media!
The various forms of optical storage include the ubiquitous CDs, the superior DVDs, the ancient laserdiscs, and the up-and-coming powerhouses HD-DVD and Blu-Ray discs. Optical storage media can also be classified according to their reading technology, giving birth to a slew of acronyms – the read-only CD, CD-ROM, DVD-ROM, and DVD-Video; the write-once CD-R and DVD-R, both of which use WORM technology; and the rewritable CD-RW, DVD-RAM, and DVD-RW.
To ease the load on your mind, the R in CD-R and DVD-R means "Recordable", RW means "Rewritable", ROM means "Read Only Memory", RAM means "Random Access Memory", and WORM means "Write-Once, Read-Many-times". For more information on CDs, DVDs, and their variants, please look up their respective articles.
Most optical storage media are optical disks, such as CDs. The data on optical disks are usually accessed by a laser beam touching the disc's surface. A 'sub-type' of optical disks is the phase-change disk, which uses a material that can freeze into either a crystalline or amorphous state. Phase-change disks allow rewritable optical media, such as CD-RWs and DVD-RWs. On the other hand, magneto-optic disks straddle the line, as they're made of magnetic recordable material but use optical technology (i.e. laser) to record the data.
Optical storage media can also be grouped by generation; more on this in The History of Optical Storage.
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