Disasters  include...

• fire, flood, lightning, hurricanes, bombs,...
• hardware failure - eg hard drive head crash
• software failure - resource problems or bugs in the system
• deliberate vandalism / hacking
• accidental altering of data eg by inexperienced employees.
• networks may go down preventing communication.

Companies need to make sure that in their computer systems there are adequate disaster recovery procedures.

• risk analysis, 
• preventive measures
• staff training.

• what response should staff make when the disaster occurs.

• recovery measures

Hardware can be easily (possible expensively!) replaced.

Software can be re-installed. (or de-bugged by the programming department).

The real problem is the data. No business can afford to lose its data. 

Backups of all data should be regularly made. This means that the worst case scenario is that the business has to go back to the situation of the last backup and carry on from there. Backups may take a long time - often tape-streamed at night.

Alternative communication systems may be arranged in case a network goes down.