ABSTRACT
The process computers were used for direct digital control. A system is usually evaluated in terms of its dependability. Dependability is more than reliability or availability –it also includes security and integrity. Due to continued technological developments, computers will become increasingly reliable. Whenever reliability is analysed, it is important to include the data channel or channels in the analysis. Diagnostic and security actions have to be taken when malfunctions are detected to alert the operator and protect the system. Usually error counters are maintained which display, for example, parity errors, security disconnect errors, or time out errors. Most systems are able to correct single-bit memory errors without affecting processor operation. Some other useful integrity checks on modern systems are: power failure detection and recovery, regular disk read and write checks, and a check on the correct computation of control algorithms.
