A comparison of parallel machine models from the point of view of scalability

We compare various models of parallel machines and show that they can be classified in two classes: algorithm oriented or execution oriented. None of them are really satisfying from the user´s point of view. Hence bridging models have been proposed. Contrarily to what is done in sequential where a two-level decomposition is used (programmimg-compiling), we assert that a parallel programming methodology must be based on a three-level decomposition. We define the notion of algorithms which scales on a distributed memory parallel computer. We propose such a methodology and advocate its advantages. Then we point out the main difficulties in parallel programming