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Large-Capacity Removable Disks

Large-capacity removable disks are virtually the same as small-capacity removable disks except they can store more data (more than 500MB per disk). The drives and media cost more, but the increase in capacity easily offsets the increased cost. Large-capacity removable disks are good for backing up a workstation that has only one or two disks. You can also use them to back up a server, but because they don’t have the capacity to back up a server with a single removable disk (multiple disks would be required for each backup), their use is limited. Table 9.2 lists a few of the common large-capacity removable disks and their capacities.

9.2 Popular Large-Capacity Removable Disks

Medium    Capacity

Iomega Jaz    1GB, 2GB

Sharq    1.5GB

SyQuest cartridges    1GB, 1.5GB

Removable hard-disk drive    Varies

Removable Optical Disks

Removable optical disks use a laser (or some kind of light beam) to read and write information stored on a removable disk. They typically have large capacities and are fairly slow (more than 100 milliseconds as opposed to less than 50 milliseconds for magnetic) access times. The advantage to optical disks is that the capacities start at about 128MB and go up from there (650MB is a common size). There are even special optical jukeboxes, containing hundreds of disks and a robotic arm to select disks and put them in the drive(s), that have capacities in the hundreds of terabytes (1 terabyte is 1024 gigabytes). Table 9.3 lists some of the popular optical formats and their capacities.

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