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The Main Architectural Classes

Since many years the taxonomy of Flynn[2] has proven to be useful for the classification of high-performance computers. This classification is based on the way of manipulating of instruction and data streams and comprises four main architectural classes. We will first briefly sketch these classes and afterwards fill in some details when each of the classes are described separately.

Although the difference between shared- and distributed memory machines seems clear cut, this is not always entirely the case from user's point of view. For instance, the late Kendall Square Research systems employed the idea of ``virtual shared memory'' on a hardware level. Virtual shared memory can also be simulated at the programming level: The first draft proposal for High Performance Fortran (HPF) was published in November 1992 [3] which by means of compiler directives distributes the data over the available processors. The proposal was fixed by May 1993. Therefore, the system on which HPF is implemented will act in this case as a shared memory machine to the user. Other vendors of Massively Parallel Processing systems (the buzz-word MPP systems is fashionable here), like Convex and Cray, also support proprietary virtual shared-memory programming models which means that these physically distributed memory systems, by virtue of the programming model, logically will behave as shared memory systems.

A very large majority of the systems appearing in the TOP500 are either of the shared memory MIMD class (large vector processors) or of the distributed memory MIMD class with a large amount of processors. The reason is that the individual processors of the latter class are mostly off-the-shelf RISC processors which have a lower single node performance than the vectorprocessors in the former class. Still, by their shear number they may perform at the same level as the large vector processors on certain applications. This is certainly true for the LINPACK benchmark used in this report.

We will not discuss in full the various machine properties for all relevant systems (such an overview could for instance be found in [4]), but we will give a short charactersation of each machine of interest that might help in understanding how the performance for these systems came about.



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Next: Description of Machine Up: Short Description of Archictectures Previous: Short Description of Archictectures



top500@rz.uni-mannheim.de
Tue Nov 14 15:39:09 PST 1995