CD vs CD-ROM

CD is a generic term for Compact Disk - think "Book". CD-ROM is a type of CD, specifically "Read Only Memory" - the data on it is "fixed", it may be read only, it cannot be altered. A CD-R on the other hand may be written to, though once written to the disk, the data cannot be changed. A CD-RW may be written to, erased, altered, or overwritten. CD-R means more or less "Recordable CD", while CD-RW means more or less "Re-Writable CD"


Hope I didn't confuse you further.

I think that technically a CD-R, once written, would still not be considered CR-ROM even though it is read only memory, because I suspect that there may be differences in the way the data is actually burned into the disk, and perhaps with the encoding standard. At least, in digital memory read only memory is stored very differently than rewritable memory, so I'm presuming that there may be a difference here too.

Strictly speaking, a CD-ROM would be a commercially produced disk, typically manufactured in high volume, such as an audio CD or a program installation CD. The manufacturing process of the end-user product does not involve "burning", but rather is effected through "stamping". A master, or "Father", disk, based on a photochemically treated ultra smooth glass substrate which is then metalized via a multi-step process, is used to produce "Mother" disks, essentially mirror-image replications of the "Father" disk, from which are produced the "Son" disks, or "Stampers", which are used to "Stamp" the retail product disks. "Stamping" is achieved through automatic process consisting of injecting semi-molten polycarbonate plastic into a mold containing a "Stamper", injection pressure forcing the semi-molten plastic to conform to the pits and ridges of the "Stamper", removing the "raw" or "green" plastic disk from the mold, metalizing, or electroplating the disk in a high-vacuum chamber, then spin-coating the metalized disk with a tough, transparent, UV-cured laquer which both protects the metalized pit-and-grove surface from tarnishing and provides a printable surface. Using "Stampers", a machine like this:

will output thousands of disks per hour, ready for label printing and packaging. Naturally, both labeling and packaging are automated as well; a production facillity employs relatively few workers, the machines more or less"doing it all" - administrative, office, and maintenance staff generallyfar outnumber actual production staff. Not considering the cost of the information carried by the CD, labeling, packaging, and distribution, production cost for very high-volume runs can be in the fraction-of-a-cent-per-unit range, though more typical runs wil be in the few-cents-per-unit range. Administrative, labeling, packaging, and distribution costs amount to a significant multiple of physical production cost, then the intellectual property cost must be factored in, on top of all of which which goes the retailer's profit margin. Though considerably less expensive to produce and bring to market than were vinyl records or cassette and video tapes, CDs and DVDs sell at a premium compared to their predecessors. And the music and movie industries complain they're going broke.