ABSTRACT
The measure of a device’s reliability is the infrequency with which failures occur in time. There are many physical causes that individually or collectively may be responsible for the failure of a hardware component or device at any particular instant. It is not always possible to isolate these physical causes and mathematically account for all of them. Similarly, it is not always possible to determine the non-physical causes for failures of software components or devices. However, in both cases, it is not only possible, but of utmost importance, to define what constitutes a failure for a particular device. This definition will depend not only on the architecture of the device but on the environment in which it is used and the intended application as well.
