Tape versus disk

Magnetic tape and disks both use the same basic technology of a thin magnetic layer on a plastic backing.

Advances in physics technology have resulted in higher and higher packing densities.

It is possible to purchase cassette based tape storage systems for less than £ 100. Tape cassettes cost between £ 12 to £ 20 depending on capacity, and can store up to about 3 Gb.

It is also possible to purchase interchangeable disk based systems for around £ 100. Disks cost around £ 10 each, and can store 100 Mb.

Ignoring the prices of the drive units ( which are very similar ), a tape based storage system therefore costs around £ 10 per 1 Gb of storage capacity; an interchangeable disk based system costs around £ 100 per 1 Gb.

So a tape based system is much cheaper to implement for very large storage capacity.

However there is a significant disadvantage with tape based systems, in that the data is recorded serially along the tape - retrieving data can therefore involve long access times.

In contrast, a disk based system can offer random access, with access times typically 20 to 50 msec.

In general terms therefore, for archive storage it is more economic to use tape; for on-line back up storage it is faster to use disk.

© 1998 Ron Turner

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