The following are examples of optical disks: CD-ROM (ReadOnly), WORM (WriteOnce~ReadMany), and magneto-optical (ReadManyWriteMany). Currently, no procedures exist that are considered adequate to ensure purging of these media. Magneto-optical disk technology uses a combination of laser optics and magnetics to obtain data densities far surpassing those of magnetic disks alone. Magneto- optical disks can be cleared by a single overwrite, although purging by overwrite is not considered adequate.
This technology couples magnetics with semiconductor random access memory to provide data retention after power is removed. There have been no standards published providing procedures to ensure clearing or purging of these media. However, consistency with all other types of storage media would dictate that a single overwrite is sufficient for clearing.
As noted earlier in Section 4.6, "Overwrite Software and Purging," many drawbacks exist to using overwrite software for purging disks. Some of these drawbacks are not applicable to disk exercisers, which use a dedicated operating system. Winchester disk manufacturers use disk exercisers to do as their name implies-put Winchester disk drives through their paces. To purge a Winchester drive, the Winchester unit must be plugged into the disk exerciser. The disk exerciser is able to write to any part of a disk regardless of whether the operating system labeled the sector unusable. Some of these "exercisers" also have the capability of writing at different frequencies. This makes them a more effective alternative to overwrite software; however, their ability to purge disks has not been tested.