Unformatted text preview: ng system. The operating system has two primary purposes: (1) To protect the hardware from misuse by runaway applications, and (2) To provide applications with simple and uniform mechanisms for manipulating complicated and often wildly different low-level hardware devices. The operating system achieves both goals 12 CHAPTER 1. INTRODUCTION application programs operating system processor main memory I/O devices software hardware Figure 1.10: Layered view of a computer system. via the fundamental abstractions shown in Figure 1.11: processes, virtual memory, and ﬁles. As this ﬁgure
processes virtual memory files processor main memory I/O devices Figure 1.11: Abstractions provided by an operating system. suggests, ﬁles are abstractions for I/O devices. Virtual memory is an abstraction for both the main memory and disk I/O devices. And processes are abstractions for the processor, main memory, and I/O devices. We will discuss each in turn.
Aside: Unix and Posix. The 1960s was an era of huge, complex operating systems, such as IBM’s OS/360 and Honeywell’s Multics systems. While OS/360 was one of the most successful software projects in history, Multics dragged on for years and never...
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