Structural Classification

Flynn's classification explains the behavioural idea and doesn't take concern into the computer's structure. Parallel computers can be categorized based on their organization also, that is discussed below and shown in Figure below. As we have seen a parallel computer (MIMD) can be explained as a set of numerous processors and mutual memory or memory modules communicating through an interconnection network. When multiprocessors communicate via the universally shared memory modules then this organisation is termed as tightly coupled systems or Shared memory computer as shown in Figure. In the same way when every processor in a multiprocessor system has its own local memory and the processors communicate through messages broadcasted between their local memories then this organisation is termed as 'Loosely coupled system' or 'Distributed memory computer' as shown in Figure. Figures 1 and 2 shows the simplified diagrams of both organisations together. The memory and processors in both organisations are interrelated by an interconnection network. This interconnection network can be in different forms such as multistage network and crossbar switch. 

                                                              Figure 1: Structural classification

Figure 2: Tightly coupled system

Figure 3: Loosely coupled system