Operating System Concepts Essentials, Second Edition

Main Memory

In Chapter 6, we showed how the CPU can be shared by a set of processes. As a result of CPU scheduling, we can improve both the utilization of the CPU and the speed of the computer's response to its users. To realize this increase in performance, however, we must keep several processes in memory—that is, we must share memory.

In this chapter, we discuss various ways to manage memory. The memory-management algorithms vary from a primitive bare-machine approach to paging and segmentation strategies. Each approach has its own advantages and disadvantages. Selection of a memory-management method for a specific system depends on many factors, especially on the hardware design of the system. As we shall see, many algorithms require hardware support, leading many systems to have closely integrated hardware and operating-system memory management.

CHAPTER OBJECTIVES

• To provide a detailed description of various ways of organizing memory hardware.
• To explore various techniques of allocating memory to processes.
• To discuss in detail how paging works in contemporary computer systems.

7.1 Background

As we saw in Chapter 1, memory is central to the operation of a modern computer system. Memory consists of a large array of bytes, each with its own address. The CPU fetches instructions from memory according to the value of the program counter. These instructions may cause additional ...