The performability of degradable heterogeneous computer systems containing k > 1 types of components is considered. Previous analyses of such systems have been numerical in nature and yielded algorithms with either exponential complexity in the number of system states n, or polynomial in n with approximate truncations of infinite series. In this paper, a closed form expression for the performability of degradable heterogeneous systems is derived. Furthermore, an algorithm with polynomial complexity, O(kn3), is presented and applied to study the performability of a multiprocessor computer system. Copyright © 1987 by The Institute of Electrical and Electronics Engineers, Inc.