Optical disk media are a smaller range of solutions than perhaps hard disk or tape. Within this narrower field of a few key suppliers of media these products are integrated by a slightly wider field of systems providers. Systems can typically accommodate successive generations of media from a particular manufacturer with minimal disruption.

Optical disks offer an archive platform with true write once, read many (WORM(g)) capability. This ability may lead you to assume that once content is commited to an optical format, it will probably stay on those disks for many years to come. Physically the disks can indeed retain the data for many years, but the pressures to migrate are not driven by a fear that your data will disappear. Rather, the pressure is due to the concern that the disks will be unreadable, because the technology is no longer supported.

This is a sensible concern. Optical disks, even the apparently backward compatible(g) CDs, CD-Rs, and DVDs may well lose their backward compatibility during the lifetime of your archive. Just because a media is 3 inches across and fits a CD drive does not ensure that the drive will read it, and in future, the likelihood of the disk and the drive being compatible will diminish.