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.<>