5.1. Terminology

A central component of any operating system is the memory-management system. As the name implies, memory-management facilities are responsible for the management of memory resources available on a machine. These resources are typically layered in a hierarchical fashion, with memory-access times inversely related to their proximity to the CPU (see Fig. 5.1). The primary memory system is main memory; the next level of storage is secondary storage or backing storage. Main-memory systems usually are constructed from random-access memories, whereas secondary stores are placed on moving-head disk drives. In certain workstation environments, the common two-level hierarchy is becoming a three-level hierarchy, with the addition of file-server machines connected to a workstation via a local-area network [Gingell, Moran, & Shannon, 1987].

Figure 5.1. Hierarchical layering of memory.