Educational Applications Abound for Optical Drives
Audio compact disc (CD) players were the consumer passion of the 1980s. In the 1990s, educators will likely become passionate over optical disc drives linked to their computers. The allure of 600MB of existing data or pure storage space on a single 5.25" optical disc is hard to resist.
There are currently three types of optical disc drives for computers: CD-ROM, WORM and erasable. Each drive uses a corresponding type of disc, and it is not possible to mix-and-match. For example, one cannot play a WORM disc in a CD-ROM drive (although you can play a music CD in a CD-ROM drive).
Here's the basics: CD-ROM stands for "compact disc-read only memory"--these CDs come with data already on them. They can be read but not altered. WORM stands for "write once, read many"; these blank discs are writable and readable but not rewritable. And erasable CDs are blank discs that can be written to, erased and rewritten to repeatedly.
Optical disc drives are available in two physical configurations: external units ready to be cabled to a host computer, or internal units designed to be installed inside a computer.
In order for a host computer to use the optical drive, an interface card called a controller is required. Some of the newer drives have controllers already embedded. Another feature to look for in drives is built-in memory that serves as a data buffer. The bigger the buffer, measured in terms of kilobytes (K), the better.
Optical disc drives actually work upside down. All reading and writing operations are done with a tiny laser beam that shines through the bottom of the disc. Reading is accomplished by measuring the amount of light reflected back; writing is done with heat generated by the laser.
Technically, optical drives are much slower in terms of average access time than hard disk drives. In environments where extensive reading of and writing to disc are the norm, optical drives are not yet fast enough to replace traditional hard drives. However, other situations are tailor-made for optical drives. These include archiving and backup operations; document storage; acting as a file server in some instances; and working with subjects that require large, contigous files, such as music, video, CAD and multimedia.
The Media Itself
Of course, optical disc drives are only the medium for the message--and the message, in this case, is media.
A compact disc has multiple layers. The surface is a silk-screened label; next is a protective layer of clear acrylic. Then there's a reflective aluminum layer (on CD-ROMs only); and finally comes a layer of polycarbonate substrate. This last layer accounts for 99 percent of the thickness of the disc and is the part that actually holds the data. Writable optical media, such as WORM and erasable CDs, don't have the aluminum layer, making them translucent, often with a bluish tint.
Most CD-ROM drives use caddies to hold discs. A caddy is a hard plastic case that protects the media and provides drives with an easier way to grab and load discs. WORM and erasable drives use media cartridges similar to the cases around 3.5" microfloppies.
Currently, CD-ROM drives are the most common of all optical drives being used in education. …