This paper deals with the reliability and fault-tolerance evaluation of multiprocessor and multicomputer architectures considering the degradation of both computation and communication capabilities. Reliability and performance availability (pa) are used to characterize and evaluate the dependability of these architectures. Bandwidth availability (ba) and computation-communication availability (cca) are used to quantify thepa of multiprocessors and multicomputers, respectively. These measures are based on the system requirements for the parallel execution of a task (job) that consists of a few subtasks. We present two different dependability models for multiprocessors, namely: a bus-oriented model (bom) and a switch-oriented model (som). Thebom is an analytical model and is used to evaluate multiprocessors with crossbar and multiple-bus interconnections. Thesom uses simulation to analyze all types of multiprocessors. A simulation technique is also presented to compute the reliability andcca of various types of multicomputer networks suggested in the literature.