Sistemas Operativos

CHAPTER

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Introduction
Practice Exercises
1.1 What are the three main purposes of an operating system? Answer: The three main puropses are:

• To provide an environment for a computer user to execute programs
on computer hardware in a convenient and efficient manner.

• To allocate the separate resources of the computer as needed to
solve the problem given. The allocation processshould be as fair and efficient as possible.

• As a control program it serves two major functions: (1) supervision
of the execution of user programs to prevent errors and improper use of the computer, and (2) management of the operation and control of I/O devices. 1.2 What are the main differences between operating systems for mainframe computers and personal computers? Answer: Generally,operating systems for batch systems have simpler requirements than for personal computers. Batch systems do not have to be concerned with interacting with a user as much as a personal computer. As a result, an operating system for a PC must be concerned with response time for an interactive user. Batch systems do not have such requirements. A pure batch system also may have not to handle time sharing,whereas an operating system must switch rapidly between different jobs. List the four steps that are necessary to run a program on a completely dedicated machine —a computer that is running only that program. Answer: The four steps are: a. b. c. Reserve machine time. Manually load program into memory. Load starting address and begin execution.
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1.3

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Chapter 1 Introduction

d. 1.4Monitor and control execution of program from console.

We have stressed the need for an operating system to make efficient use of the computing hardware. When is it appropriate for the operating system to forsake this principle and to “waste” resources? Why is such a system not really wasteful? Answer: Single-user systems should maximize use of the system for the user. A GUI might “waste” CPUcycles, but it optimizes the user’s interaction with the system. What is the main difficulty that a programmer must overcome in writing an operating system for a real-time environment? Answer: The main difficulty is keeping the operating system within the fixed time constraints of a real-time system. If the system does not complete a task in a certain time frame, it may cause a breakdown of the entiresystem it is running. Therefore when writing an operating system for a real-time system, the writer must be sure that his scheduling schemes don’t allow response time to exceed the time constraint. Consider the various definitions of operating system. Next, consider whether the operating system should include applications such as Web browsers and mail programs. Argue both that it should and that itshould not, and support your answers. Answer: Point. Applications such as web browsers and email tools are performing an increasingly important role in modern desktop computer systems. To fulfill this role, they should be incorporated as part of the operating system. By doing so, they can provide better performance and better integration with the rest of the system. In addition, these importantapplications can have the same look-and-feel as the operating system software. Counterpoint. The fundamental role of the operating system is to manage system resources such as the CPU, memory, I/O devices, etc. In addition, it’s role is to run software applications such as web browsers and email applications. By incorporating such applications into the operating system, we burden the operating systemwith additional functionality. Such a burden may result in the operating system performing a less-thansatisfactory job at managing system resources. In addition, we increase the size of the operating system thereby increasing the likelihood of system crashes and security violations. How does the distinction between kernel mode and user mode function as a rudimentary form of protection (security)...