Optical Storage

How it Works

Optical storage devices use a laser to read data on optical disks. Pits and lands on the surface of the disk store the data as 1's and 0's. Lands are the dark spots or the 1's. Pits are light spots or the 0's. The optical disks are proteced by a clear plasticexternal image ict04datastorage.gif covering.Scratches, figerprints, and dust will all corrupt the data. The plastic prevents the pits and lands form being destroyed and the data corrupted. All CD's and DVD's use random access.

CD's and DVD's are either made with recordable or rewritable technology. Both technologies are means of storing data on optical disks permanently, but rewritable is far more versatile because it is not indelible.

Recordable technology uses a laser to change color in a dye layer beneath a clear plastic disk surface. The dark spots in the dye are permanent and cannot be changed.

Rewritable technology uses "phase change" technology to change the structure on the disk surface creating pits and lands. These can be changed from a light spot to a dark spot and back again, and it continues repeating.

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  • external image Laserdisc.jpgCD-ROM (read only memory) Data is stamped on the disk at the time it is manufactured and cannot be altered.
* DVD-ROM Data is stamped on at the time of manufacturing; data cannot be altered.
  • DVD+R/ DVD-R (recordable) Disks store data using recordable technology. Data cannot be altered.
  • CD-RW (rewritable) Disks store data using rewritable technology. Stored data can be recorded and erased multiple times. It has CD storage capacity.
  • DVD+RW/ DVD-RW Disks store data using rewritable technology. DVD+RW/DVD-RW work the same as CD-RW disks. They can be erased, modified, and offer a flexible storage capacity.

The Difference

external image CD-Blank.gif Contrary to popular belief, CD's and DVD's are not the same. The technology is similar, but the storage capacaties differ in a variety of ways. CD's can hold up to 700 MB of data or music files, while DVD's range from 4.7 GB to the 8.5 GB of a double layer DVD. The Blu-Ray DVD can hold up to 25 GB of data.

One day, will all CD's become DVD's? Will CD drives become capable of playing DVD's? It is important to understand the technology of evolving disk technology and capabilities in order to adapt to the ever-changing information age.