计算机系统与Java软件开发基础

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"Java软件解决方案" 本章节将探讨 Java 软件解决方案的基础知识，涵盖硬件和软件之间的协作关系、软件类型、计算机组件、计算机网络、Internet 和 World Wide Web 的影响、Java 编程语言、程序编译和执行过程、图形表示等方面。首先，让我们来探讨硬件和软件之间的协作关系。硬件和软件都是计算机系统的组成部分，它们之间的协作关系是计算机系统能够完成复杂任务的基础。硬件提供了计算机系统的物理基础，而软件则提供了指令和数据处理的逻辑基础。硬件和软件之间的协作关系是紧密的，软件的执行依赖于硬件的支持，而硬件的功能又受到软件的控制。在了解硬件和软件之间的协作关系后，让我们来定义各种类型的软件。软件可以分为系统软件和应用软件两大类。系统软件负责管理计算机系统的资源，提供了基本的操作环境，而应用软件则是为了完成特定的任务而设计的。常见的应用软件有文字处理软件、图形设计软件、游戏软件等。在了解软件类型后，让我们来了解计算机的核心组件。计算机的核心组件包括中央处理器（CPU）、内存（RAM）、存储器（Hard Disk）和输入/输出设备等。这些组件之间的协作关系是计算机系统能够执行程序和管理数据的基础。在了解计算机的核心组件后，让我们来了解计算机之间的连接关系。计算机之间的连接可以形成计算机网络，计算机网络使得多台计算机能够共享资源和信息。计算机网络的出现 револю化了计算机的使用方式，使得计算机能够在更多的场景下发挥作用。在了解计算机网络后，让我们来了解 Internet 和 World Wide Web 的影响。Internet 是全球最大的计算机网络，使得全球的计算机能够相互连接和共享信息。World Wide Web 则是基于 Internet 的一个分布式超媒体系统，使得用户能够便捷地访问和共享信息。在了解 Internet 和 World Wide Web 的影响后，让我们来介绍 Java 编程语言。Java 是一种高级编程语言，能够在多种平台上运行。Java 的出现使得软件开发变得更加灵活和高效。在了解 Java 编程语言后，让我们来了解程序编译和执行过程。程序编译是将源代码翻译成机器代码的过程，而程序执行是将编译后的机器代码执行的过程。程序编译和执行过程是软件开发的核心步骤。最后，让我们来介绍图形表示。图形表示是计算机图形学的基础，能够使得用户更好地理解和使用计算机系统。图形表示有多种形式，如二维图形、三维图形等，每种形式都有其特点和应用场景。本章节涵盖了 Java 软件解决方案的基础知识，包括硬件和软件之间的协作关系、软件类型、计算机组件、计算机网络、Internet 和 World Wide Web 的影响、Java 编程语言、程序编译和执行过程、图形表示等方面，为读者提供了一个系统的 Java 软件解决方案的入门知识。

16 CHAPTER 1 computer systems

Tapes are usually used only to store information when it is no longer used fre-

quently, or to provide a backup copy of the information on a disk.

Two other terms are used to describe memory devices: random access memory

(RAM) and read-only memory (ROM). It’s important to understand these terms

because they are used often, and their names can be misleading. The terms RAM

and main memory are basically interchangeable. When contrasted with ROM,

however, the term RAM seems to imply something it shouldn’t. Both RAM and

ROM are direct (or random) access devices. RAM should probably be called

read-write memory, since data can be both written to it and read from it. This fea-

ture distinguishes it from ROM. After information is stored on ROM, it cannot

be altered (as the term “read-only” implies). ROM chips are often embedded into

the main circuit board of a computer and used to provide the preliminary instruc-

tions needed when the computer is initially turned on.

A CD-ROM is a portable secondary memory device. CD stands for compact

disc. It is accurately called ROM because information is stored permanently when

the CD is created and cannot be changed. Like its musical CD coun-

terpart, a CD-ROM stores information in binary format. When the CD

is initially created, a microscopic pit is pressed into the disc to repre-

sent a binary 1, and the disc is left smooth to represent a binary 0. The

bits are read by shining a low-intensity laser beam onto the spinning

disc. The laser beam reflects strongly from a smooth area on the disc

figure 1.12 A hard disk drive with multiple disks and read/write heads

Disks

Read/write

head

The surface of a CD has both

smooth areas and small pits. A

pit represents a binary 1 and a

smooth area represents a

binary 0.

key

concept

1.1 hardware components 17

but weakly from a pitted area. A sensor receiving the reflection determines

whether each bit is a 1 or a 0 accordingly. A typical CD-ROM’s storage capacity

is approximately 650 MB.

Variations on basic CD technology have emerged quickly. It is now common

for a home computer to be equipped with a CD-Recordable (CD-R) drive. A

CD-R can be used to create a CD for music or for general computer storage. Once

created, you can use a CD-R disc in a standard CD player, but you can’t change

the information on a CD-R disc once it has been “burned.” Music CDs that you

buy in a store are pressed from a mold, whereas CD-Rs are burned with a laser.

A CD-Rewritable (CD-RW) disc can be erased and reused. They can

be reused because the pits and flat surfaces of a normal CD are simu-

lated on a CD-RW by coating the surface of the disc with a material

that, when heated to one temperature becomes amorphous (and there-

fore non-reflective) and when heated to a different temperature

becomes crystalline (and therefore reflective). The CD-RW media

doesn’t work in all players, but CD-Rewritable drives can create both

CD-R and CD-RW discs.

CDs were initially a popular format for music; they later evolved to be used as

a general computer storage device. Similarly, the DVD format was originally cre-

ated for video and is now making headway as a general format for computer

data. DVD once stood for digital video disc or digital versatile disc, but now the

acronym generally stands on its own. A DVD has a tighter format (more bits per

square inch) than a CD and can therefore store much more information. It is

likely that DVD-ROMs eventually will replace CD-ROMs completely because

there is a compatible migration path, meaning that a DVD drive can read a CD-

ROM. There are currently six different formats for recordable DVDs; some of

these are essentially in competition with each other. The market will decide which

formats will dominate.

The speed of a CD drive is expressed in multiples of x, which represents a data

transfer speed of 153,600 bytes of data per second. The CD-RW drive described

in Fig. 1.8 is characterized as having 24x/10x/40x maximum speed, which means

it can write data onto CD-R discs at 24x, it can write data onto CD-RW discs at

10x, and it reads data from a disc at 40x.

The capacity of storage devices changes continually as technology improves. A

general rule in the computer industry suggests that storage capacity approx-

imately doubles every 18 months. However, this progress eventually will slow

down as capacities approach absolute physical limits.

A rewritable CD simulates the

pits and smooth areas of a

regular CD using a coating

that can be made amorphous

or crystalline as needed.

key

concept

program counter is incremented at this point to prepare for the next

cycle. Then the instruction is decoded electronically to determine

which operation to carry out. Finally, the control unit activates the cor-

rect circuitry to carry out the instruction, which may load a data value

into a register or add two values together, for example.

The CPU is constructed on a chip called a microprocessor, a device that is part

of the main circuit board of the computer. This board also contains ROM chips

and communication sockets to which device controllers, such as the controller

that manages the video display, can be connected.

Another crucial component of the main circuit board is the system clock. The

clock generates an electronic pulse at regular intervals, which synchronizes the

events of the CPU. The rate at which the pulses occur is called the clock speed,

and it varies depending on the processor. The computer described in Fig. 1.8

includes a Pentium 4 processor that runs at a clock speed of 950 megahertz

(MHz), or approximately 950 million pulses per second. The speed of

the system clock provides a rough measure of how fast the CPU exe-

cutes instructions. Similar to storage capacities, the speed of processors

is constantly increasing with advances in technology, approximately

doubling every 18 months.

1.2 networks

A single computer can accomplish a great deal, but connecting several computers

together into networks can dramatically increase productivity and facilitate the

sharing of information. A network is two or more computers connected together

so they can exchange information. Using networks has become the normal mode

1.2 networks 19

figure 1.14

The continuous fetch-decode-execute cycle

Fetch an instruction

from main memory

Execute the instruction

Decode the instruction

and increment program

counter

The von Neumann architecture

and the fetch-decode-execute

cycle form the foundation of

computer processing.

key

concept

The speed of the system clock

indicates how fast the CPU

executes instructions.

key

concept

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