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TABLE 9.3 Popular Removable Optical Disk Capacities


Common Capacities



Magneto Optical disk

650MB, 1.3GB, 4.6GB


4.7GB up to 17GB

CD-R and CD-RW are writable CD-ROM implementations.

Magnetic Tape

Magnetic tape is the oldest and most popular backup medium for offline (not readily accessible) data storage. It stores data in the form of magnetically-oriented metal particles (either copper oxide or chromium dioxide) on a polyester tape. It is popular because it is simple, inexpensive, and has a high capacity. Most networks use a magnetic tape backup of some kind. Table 9.4 lists a few of the most common magnetic tape backup technologies and their common capacities.

Servers must be backed up because they contain all the data for the entire network. In most networks, workstations are not backed up because they usually don’t contain any data of major importance. (Individual workstations would be backed up only if the users are trained properly and store all their data on the network.) Users can mistakenly save their data to their local workstation. Also, user application configuration data are normally stored on the workstation. If a workstation’s hard disk goes down, the configuration is lost.

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