A comparison of shared and nonshared memory models of parallel computation

Four algorithms are analyzed in the shared and nonshared (distributed) memory models of parallel computation. The analysis shows that the shared memory model predicts optimality for algorithms and programming styles that cannot be realized on any physical parallel computers. Programs based on these techniques are inferior to programs written in the nonshared memory model. The unit cost charged for a reference to shared memory is argued to be the source of the shared memory model´s inaccuracy. The implications of these observations are discussed