3.3.8 Reliability

Backups are only useful if they can be read (!) Therefore it is vital to check from time to time that backups made automatically can actually be restored .

The reliability of Computer Systems varies according to the nature of the task they carry out. In some cases it is not a complete disaster if they fail - eg if the hard disc on your computer crashes and destroys your homework it may or may not be a terrible event.

Computer systems dealing with commerce can be vital to personal and national economies ; large banks, insurance companies, airlines and shipping lines for example. In these types of system, data is backed up both on site and off site. Terrible as the bombing of New York's twin towers was, businesses based there were able to carry on thanks to the fact that the data was safely backed up elsewhere.

Yet other computer systems maintain safe operations, eg air traffic control , hospital patient monitoring systems, nuclear power station control systems, etc. In these cases, mirrored systems are often used so that of one fails , the other is immediately ready to take over.

In extreme cases, triple systems may be used.

We noted already on the previous page that a master file can be re-created from the previous master file and the transaction file. In batch processing , three generations of master and transaction files are usually kept. This is sometimes called the Grandfather, Father, Son method of backup.

Backup utilities are also used to keep copies of important files. These backups maybe full (a new copy made of every file on the system) or incremental (only new and changed files are saved).

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related: [ Common core home | previous: types of processing | next: networks (intro) ]

Data is vital to the operation of a commercial business, therefore it is looked after very carefully.

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