Today, CD-ROM (or CD for short) is the most widespread storage medium for large amounts of data due to the
CD drives can either hold a single CD or have a CD changer subsystem which holds up to 7 CDs (changing CDs in a multi-CD system requires about 5 secs).
The major restriction of CDs is that they are a read-only storage medium. A CD is mastered on a hard disk the contents of which are then copied to a tape. This tape is sent to a production site which produces a glass master CD which then serves to produce metal master CDs. These metal master CDs are used to press the final CD copies.
CD-R is a write once/read many (WORM) storage medium. In contrast to pressed CDs the data is recorded on special virgin CD-R disks by burning a pattern into the reflective substrate of the CD-R. This process is irreversible. A CD-R can be read by any CD-ROM drive.
Producing CDs individually has two important consequences:
The major drawback of CD-R is that their longevity is reduced. CD-Rs come with a one year limited warranty only. However, one can expect data to be safe on CD-R for approx. 10 years if the medium is not exposed to high temperatures or ultraviolet radiation (which may affect the reflective stratum).