Unlike many other operating systems, Amoeba is a distributed operating system that provides group communication (i.e. one-to-many communication). The authors discuss design issues for group communication, Amoeba's group system calls, and the protocols to implement group communication. To demonstrate that group communication is a useful abstraction, they describe a design and implementation of a fault-tolerant directory service. They discuss two versions of the directory service: one with non-volatile RAM (NVRAM) and one without NVRAM. They give performance figures for both implementations.