Recordable CD-ROMs

Part III

Welcome to the third part of the How It Works: Optical Storage guide. Today we are going to talk about optical recording technology, and then we'll go over the newest incarnation of optical storage devices, the DVD-ROM. We will also discuss recordable DVD technology.

The WORMs are here!

Recordable CD-ROM drives are still a fairly new technology, but they have quickly become the single most popular consumer add-on component purchased in recent years. Most computer system manufacturers will install a recordable CD-ROM drive into a new computer system either as part of a package, or for a small fee as an add-on component. Recordable CD-ROM drives function on the same basic principal as standard CD-ROM drives; they are capable of reading virtually every established compact disc standard to date with the added ability of being able to write to a specially made CD-R (recordable compact disc) or CD-R/W (re-writable compact disc) media.

A CD-R is a specially designed compact disc, made specifically for writing data without going thought the complicated CD-ROM mass production method. Instead of creating a master disc and stamping out thousands of copies with expensive machinery, you can make a single inexpensive copy with a CD-R and a CD-ROM recorder. The first generation recordable CDs were dubbed "WORM" for "Write Once, Read Many." WORM drives used CD-Rs which can be written to only once, but can be read an infinite number of times by a standard CD-ROM drive.

Stamp vs. burn

Recall that standard CD-ROMs use little "pits" and "land" to encode information. As the laser hits the pits or land, the strength of the reflected laser beam is changed, and interpreted by the receiver as data. When recording data to a CD-R, the drive uses a special laser to heat the surface of the disc. The disc strata is coated with a special photosensitive layer, areas of the disc are "burned" to change their reflective values, effectively mimicking the land and pits of a mass-produced stamped CD.

A standard CD-ROM can interpret the different reflective values of the CD-Rs surface in the same way it reads data from a standard CD-ROM. However, some older CD-ROM drives, and even some newer generic brand drives might exhibit difficulty reading from a "burned" disc. This is due to the fact that older drives were not designed to read such a disc, since they were made before CD-Rs were on the market. Overall, the reflective properties of a burned disc are lower than in a mass produced CD, which can make it more difficult or impossible for older, lower quality CD-ROMs to read the burned disc.