Design of fault-tolerant computers

Causes and symptoms of logic faults in digital systems. Reliable performance of hardware has been a require-ment for digital systems since the construction of the first digital computer. Improper functioning of the logic circuits in a digital system is manifested by logic faults, which are defined for this paper as "permanent or transient deviations of logic variables from the values specified in design." Permanent faults are caused by physical changes in the components of a logic circuit which permanently alter the logic function specified by the designer. The most common permanent faults are the determinate faults of "stuck on zero " and "stuck on one " types. Less frequent is the indeterminate or "stuck on X " fault