OperatingSystems-WilliamStalling6thedition

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PART ONE

art One provides a background and context for the remainder of this book.

This part presents the fundamental concepts of computer architecture and

operating system internals.

ROAD MAP FOR PART ONE

Chapter 1 Computer System Overview

An operating system mediates among application programs, utilities, and users, on

the one hand, and the computer system hardware on the other. To appreciate the

functionality of the operating system and the design issues involved, one must have

some appreciation for computer organization and architecture. Chapter 1 provides

a brief survey of the processor, memory, and Input/Output (I/O) elements of a com-

puter system.

Chapter 2 Operating System Overview

The topic of operating system (OS) design covers a huge territory, and it is easy to

get lost in the details and lose the context of a discussion of a particular issue.

Chapter 2 provides an overview to which the reader can return at any point in the

book for context. We begin with a statement of the objectives and functions of an

operating system. Then some historically important systems and OS functions are

described. This discussion allows us to present some fundamental OS design princi-

ples in a simple environment so that the relationship among various OS functions is

clear.The chapter next highlights important characteristics of modern operating sys-

tems. Throughout the book, as various topics are discussed, it is necessary to talk

about both fundamental, well-established principles as well as more recent innova-

tions in OS design. The discussion in this chapter alerts the reader to this blend of

established and recent design approaches that must be addressed. Finally, we pre-

sent an overview of Windows, UNIX, and Linux; this discussion establishes the gen-

eral architecture of these systems, providing context for the detailed discussions to

follow.

Background

M01_STAL6329_06_SE_C01.QXD 2/13/08 1:48 PM Page 6

8 CHAPTER 1 / COMPUTER SYSTEM OVERVIEW

An operating system (OS) exploits the hardware resources of one or more processors

to provide a set of services to system users. The OS also manages secondary memory

and I/O (input/output) devices on behalf of its users. Accordingly, it is important to

have some understanding of the underlying computer system hardware before we begin

our examination of operating systems.

This chapter provides an overview of computer system hardware. In most areas,

the survey is brief, as it is assumed that the reader is familiar with this subject. However,

several areas are covered in some detail because of their importance to topics covered

later in the book.

1.1 BASIC ELEMENTS

At a top level, a computer consists of processor, memory, and I/O components, with

one or more modules of each type. These components are interconnected in some

fashion to achieve the main function of the computer, which is to execute programs.

Thus, there are four main structural elements:

• Processor: Controls the operation of the computer and performs its data pro-

cessing functions. When there is only one processor, it is often referred to as

the central processing unit (CPU).

• Main memory: Stores data and programs. This memory is typically volatile;

that is, when the computer is shut down, the contents of the memory are lost.

In contrast, the contents of disk memory are retained even when the computer

system is shut down. Main memory is also referred to as real memory or primary

memory.

• I/O modules: Move data between the computer and its external environ-

ment. The external environment consists of a variety of devices, including

secondary memory devices (e. g., disks), communications equipment, and

terminals.

• System bus: Provides for communication among processors, main memory,

and I/O modules.

Figure 1.1 depicts these top-level components. One of the processor’s func-

tions is to exchange data with memory. For this purpose, it typically makes use of

two internal (to the processor) registers: a memory address register (MAR), which

specifies the address in memory for the next read or write; and a memory buffer reg-

ister (MBR), which contains the data to be written into memory or which receives

the data read from memory. Similarly, an I/O address register (I/OAR) specifies a

particular I/O device. An I/O buffer register (I/OBR) is used for the exchange of

data between an I/O module and the processor.

A memory module consists of a set of locations, defined by sequentially num-

bered addresses. Each location contains a bit pattern that can be interpreted as ei-

ther an instruction or data. An I/O module transfers data from external devices to

processor and memory, and vice versa. It contains internal buffers for temporarily

holding data until they can be sent on.

M01_STAL6329_06_SE_C01.QXD 2/13/08 1:48 PM Page 8

10 CHAPTER 1 / COMPUTER SYSTEM OVERVIEW

There is not a clean separation of registers into these two categories. For

example, on some processors, the program counter is user visible, but on many it

is not. For purposes of the following discussion, however,it is convenient to use these

categories.

User-Visible Registers

A user-visible register may be referenced by means of the machine language that the

processor executes and is generally available to all programs, including application

programs as well as system programs. Types of registers that are typically available

are data, address, and condition code registers.

Data registers can be assigned to a variety of functions by the programmer. In

some cases, they are general purpose in nature and can be used with any machine in-

struction that performs operations on data. Often, however, there are restrictions.

For example, there may be dedicated registers for floating-point operations and oth-

ers for integer operations.

Address registers contain main memory addresses of data and instructions, or

they contain a portion of the address that is used in the calculation of the complete

or effective address. These registers may themselves be general purpose, or may be

devoted to a particular way, or mode, of addressing memory. Examples include the

following:

• Index register: Indexed addressing is a common mode of addressing that in-

volves adding an index to a base value to get the effective address.

• Segment pointer: With segmented addressing, memory is divided into segments,

which are variable-length blocks of words.

A memory reference consists of a

reference to a particular segment and an offset within the segment; this mode of

addressing is important in our discussion of memory management in Chapter 7.

In this mode of addressing, a register is used to hold the base address (starting

location) of the segment. There may be multiple registers; for example, one for

the OS (i.e., when OS code is executing on the processor) and one for the cur-

rently executing application.

• Stack pointer: If there is user-visible stack

addressing, then there is a dedi-

cated register that points to the top of the stack.This allows the use of instruc-

tions that contain no address field, such as push and pop.

For some processors, a procedure call will result in automatic saving of all user-

visible registers, to be restored on return. Saving and restoring is performed by the

processor as part of the execution of the call and return instructions.This allows each

There is no universal definition of the term word. In general, a word is an ordered set of bytes or bits that

is the normal unit in which information may be stored, transmitted, or operated on within a given com-

puter. Typically, if a processor has a fixed-length instruction set, then the instruction length equals the

word length.

A stack is located in main memory and is a sequential set of locations that are referenced similarly to a

physical stack of papers, by putting on and taking away from the top. See Appendix 1B for a discussion of

stack processing.

M01_STAL6329_06_SE_C01.QXD 2/13/08 1:48 PM Page 10

剩余798页未读，继续阅读

mlxd9466

2012-09-05

非常清晰，非常好用。感谢。

hezhen522112

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