There are several architectural models for parallel machines. Among the most prominent ones are those in Figure 18.8
processor, and disks are shown as cylinders.
? Shared memory. All the processors share a common memory (Figure 18.8a).
? Shared disk. All the processors share a common set of disks (Figure 18.8b). Shared-disk systems are sometimes called clusters.
? Shared nothing. The processors share neither a common memory nor common disk (Figure 18.8c).
? Hierarchical. This model is a hybrid of the preceding three architectures (Figure 18.8d).