Three commercial systems are considered from a programmer's point of view. The three are the Intel iPSC, a network of Inmos transputers, and the Sequent Balance. The differences in overhead are examined by implementing a solution to the traveling-salesman problem on all three. The evaluation focuses on three major issues in parallel programming: (1) how execution is divided among processing elements and how it is controlled; (2) how data are shared; and (3) how events are synchronized. The experiences of the authors are presented and some specific as well as general conclusions are drawn.