This chapter provides a short elementary introduction to parallel computers and parallel computing, and is a prerequisite for a good understanding of the following chapters. We present some architectural multiprocessor characteristics with the emphasis on distributed memory multicomputers. We discuss the hypercube topology in particular, and we illustrate its connectivity by recalling a number of well-known properties. A particular multicomputer with hypercube topology, the Intel iPSC/2, which will be used for the experiments in later chapters, is discussed in some more detail. Finally, a number of important performance parameters, such as speedup and parallel efficiency, are defined.