Flynns Classification Scheme

Parallel computers are often classified according to a scheme proposed by Michael Flynn in 1972. In the Flynn taxonomy, illustrated in Table 2.1, there are four classes of parallel computers, distinguished on the basis of the flow of data and instructions an application running on a computer is viewed as one or more sequences (or streams ) of instructions and one or more streams of data, and computers are divided into four classes depending on whether multiple streams of data or instructions are permitted. Three of these four classes of parallel computer architectures are of interest for quantum chemistry applications and are discussed in detail next. 

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This chapter provides an overview of parallel compufer architectures, including the traditional Flynn classification scheme and a discussion of computation nodes and the networks connecting them. We also present an overall system view of a parallel computer, describing the hierarchical nature of parallel archifecfure, machine reliability, and the distinction between commodity and custom computers. 

Unfortunately, Flynn s classification, although commonly used, is quite restrictive when discussing parallel-architecture computers. There have been several attempts to formulate more detailed classification schemes for the great variety of parallel computers now available. None of these efforts have been entirely successful, and none appear to be in general use. A discussion of representative machines from some of the more common classes follows. 

Parallel computers may be classified based on the flow of instructions and data as proposed by Flynn. Flynn s classification scheme divides computers into four classes ... 

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