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根据考试大纲的要求，程序员考生的英语试题难度一般。要求考生能正确阅读和理解计算机领域的简单英文资料。试题以考查计算机专业英语词汇为主，兼考语法知识。熟悉相关的计算机英文资料将有利于解答专业英语试题。
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下面按类型给出计算机专业简单的英文背景知识及参考译文。
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The essential components of a PC are the mainboard, processor and memory. The memory stores the computer program the processor is running and tile data the program needs. The mainboard is the printed circuit board that the processor and memory is mounted on. It connects the processor and memory together. Let's look at these in more detail. Remember, a computer can only work with numbers. The processor does all the calculations with the numbers, obeying the instructions in the computer program. The memory consists of tiny circuits called a memory cell. Each circuit can store a zero or a one. To make a byte of memory, you need eight of these circuits. So when you buy a 128 Meg memory strip (128 million bytes of memory), it contains 128,000, 000×8 memory cells that is, 1, 000, 000, 000 memory cells. Yet a 128 Meg memory strip is not much bigger than your finger！
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A memory strip actually contains other circuitry as well. This circuitry allows the processor to select which memory cell it wants to get data from, or to store data into. The processor can jump directly from the first memory cell to the last, then to a cell in the middle, or to anywhere else to get or store data. That's why this kind of computer memory is called Random Access Memory, or RAM for short. RAM needs electricity to be able to remember data. When you switch off your computer, all the data stored in RAM is lost. For this reason, computers need some kind of permanent storage. That's why computers have disk drives. Computer people call disk drives, magnetic tape, CDs, DVDs and so on secondary storage.
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The mainboard connects all the components of the computer together. It has electrically conducting tracks which allows electricity to flow from one component to another. For example,from the processor to the RAM.
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A computer takes some kind of input, processes it in some way, then outputs the result. For example, you scan a picture into your PC. This is the input. You then modify the graphic — you adjust the color balance, the contrast and the brightness. This is the processing. Finally, you print the graphic. This is the output.
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一台PC的主要部件有主板、处理器和存储器。存储器存储处理器正在运行的计算机程序和程序所需的数据。主板是一块印制电路板，处理器和存储器都安装在上面。它将处理器和存储器连接起来。现在就让我们来更详细地了解一下。记住，一台计算机只能处理数据。处理器遵循计算机程序中的指令对数据进行各种计算。存储器是由被称作存储单元的许多微电路组成的。每一个微电路能存储一个0或1。要构成一个字节容量的存储器，你需要8个这样的微电路。因此当你购买一块128 MB的内存条时，它包含了128 000 000×8个存储单元——也就是1 000 000 000个存储单元，然而一块128 MB的内存条还不如你的手指大。
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一块内存条实际上还包含其他电路。这些电路允许处理器选择从哪个存储单元取数据或向哪个存储单元存储数据。处理器可以从第一个存储单元直接跳转到最后一个存储单元，再到中间的存储单元，或到任意一个存储单元取数据或存储数据。这就是这类计算机存储器称作随机存取存储器，或简称RAM的原因。RAM需要有电流才能记住数据。当你关掉计算机时，在RAM中存储的所有数据就丢失了。正因为如此，计算机需要某种永久存储器。这就是为什么计算机要有磁盘驱动器。使用计算机的人将磁盘驱动器、磁带、CD、DVD等称作辅助存储器。
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主板将所有计算机部件连接在一起。它有导电电路，可使电流从一个部件流到另一个部件，例如，从处理器到RAM。
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一台计算机接收某种输入，以某种方式处理它，然后输出结果。例如：你将一幅图片扫描到你的PC中，这就是输入。接着你修改图片——调整颜色平衡、对比度和亮度，这就是处理。最后，你打印图片，这就是输出。
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Introduction of Operating System
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The operating system controls the microprocessor—just at a slightly higher level than that control unit directs activities within the microprocessor. Every cycle of a computer's microprocessor is a resource for accomplishing tasks. Many activities compete for attention of your computer's microprocessor. Commands are arriving from programs that you're using, while input is arriving from the keyboard and mouse. At the same time, data must be sent to the display device or printer, and Web pages are arriving from your Internet connection. To manage all of these competing processes, your computer's operating system must ensure that each one receives its share of microprocessor cycles. Ideally, the operating system should be able to help the microprocessor switch tasks, so that, from the user's vantage point, everything seems to be happening at the same time.
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A microprocessor works with data and executes instructions that are stored in RAM—one of your computer's most important resources. When you want to run more than one program at a time, the operating system has to allocate specific areas of memory for each program. Whilemultiple programs are running, the OS must ensure that instructions and data from one area of memory don't"leak"into an area allocated to another program. If an OS falls down on the job and fails to protect each program's memory area, data can get corrupted, programs can"crash", and your computer will display error messages, such as"General Protection Fault".
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Every device that's connected to a computer is regarded as a resource. Your computer's operating system communicates with device driver software so that data can travel smoothly between the computer and these peripheral resources. If a peripheral device or driver is not performing correctly, the operating system makes a decision about what to do—usually it displays an on-screen message to warn you of the problem.
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A user interface can be defined as the combination of hardware and software that helps people and computers communicate with each other. Your computer's user interface includes the mouse and keyboard that accept your input and carry out your commands, as well as the display device that provides cues to help you use software, and displays error messages that alert you to problems. An operating system typically provides user interface tools, such as menus and toolbar buttons, which define the"look and feel"for all of its compatible software. Most computers today feature a graphical user interface. Sometimes abbreviated"GUI"and referred to as a"gooey", a graphical user interface provides a way to point and click a mouse to select menu options and manipulate graphical objects that are displayed on the screen.
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与微处理器中控制元件的管理活动相比，操作系统只是在稍微高一级的级别上控制着微处理器。计算机微处理器的每个活动周期都是完成任务的一个资源。许多活动都要争夺处理器的关照。当通过键盘和鼠标进行输入的时候，命令也不断从你运行的程序中到达。与此同时，数据必须送到显示设备或打印机，Web页也不断从互联网中到达。为管理所有这些竞争者的进程，计算机操作系统必须保证每一个进程能够分享微处理器的周期。理想的是，操作系统应该能够帮助微处理器转换任务，因而，从用户获取利益的角度来看，所有事情就好像在同一时刻发生一样。
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微处理器要处理和执行存放在RAM——计算机中最重要的资源之一中的数据和指令。当要同时运行一个以上的程序时，操作系统必须为每个程序分配指定的内存区域。当多个程序运行时，操作系统必须保证一个内存区域中的指令和数据不能"泄漏"到已分配给另一个程序的区域中去。如果操作系统在某个任务中失败而不能保护每个程序的内存区域的话，数据就会遭到破坏，程序就会"崩溃"，计算机就会显示诸如"一般性保护错误"的出错信息。
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与计算机相连接的每一个设备都被认为是一个资源。计算机操作系统与设备驱动软件的交互使得数据在计算机和这些外部资源之间顺畅地流动。如果一个外部设备或驱动程序没有正确地工作，操作系统就会做出如何处理的决定。通常，它是在显示器上显示一个信息，以警告你出现的问题。
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用户界面可以定义为软件和硬件的结合，它帮助人与计算机进行交互。计算机用户界面包括能接收输入并执行命令的鼠标和键盘，也包括能提示如何使用软件和出现问题时提示出错信息的显示设备。操作系统一般会提供用户界面工具，如菜单和工具栏按钮等，它们为其所有兼容软件定义了"模样和感觉"。目前许多计算机都具有图形用户界面的特征。图形用户界面有时缩写为"GUI"，并被称为"大众情人"，它提供了鼠标的操作方式：用鼠标指向和单击鼠标来选择屏幕上的菜单选项和对屏幕上的图形对象进行操作。
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Database Technology on the Web
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Today's DBMS technology faces yet another challenge as researchers attempt to make sense of the immense amount of heterogeneous, fast-evolving data available on the Web. The large number of cooperating databases greatly complicates autonomy and heterogeneity issues and requires a careful scalable approach. We need better models and tools for describing data semantics and specifying metadata. Techniques for automatic data and metadata extraction and classification (ontologies, for example) are crucial for building tomorrow's Semantic Web. Query languages and query processing should also be extended to exploit semantic information.
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Users also need adaptive systems to help them explore the Web and discover interesting data sources and interfaces that support different query and search paradigms. Data dissemination techniques and notification services must be developed to enable effective data delivery services. Web-centric applications such as e-commerce and digital government applications pose stringent organizational, security, and performance requirements that far exceed what is now possible with traditional database techniques. Recent XML-native or extended DBMS still need to be fine-tuned and evaluated. Finally, we need new methodologies to support the design and development of data-intensive Web sites.
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随着研究人员试图理解网络上大量的异构、快速演化的数据，这给今天的DBMS技术带来了另一个挑战。大量的协作式数据库使自主性与异构性问题大大复杂化了，这需要一种详细的、可扩展的方法。我们需要用更好的模型和工具来描述数据语义并规定元数据。用于自动数据和元数据抽取和分类（如本体论）的技术对建立明天的语义网络至关重要。查询语言和查询过程也应扩充到能采用语义信息。
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用户也需要适应性的系统以帮助他们探索网络、发现支持不同查询和搜索范例的有趣数据源和界面。为了使数据传送服务更加有效，必须发展数据传送技术和报告服务业务。以网络为中心的应用，如电子商务和数字政府应用等，对组织、安全和性能提出了严格的要求，这些要求远远超出了目前传统数据库技术的可能性。目前本身就有XML或扩展的数据库管理系统仍需要进一步精化和评价。最后，我们需要一套新的方法来支持数据密集型网站的设计和开发。
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Conception of Software Engineering
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In August 1996 about a dozen historians met with about a dozen computer scientists to discuss the history of software engineering. The term software engineering has been deliberately chosen as being provocative at the 1968 NATO Conference on Software Engineering. This notion was meant to imply that software manufacture should be based on the types of theoretical foundations and practical disciplines that are established in the traditional branches of engineering. This need was motivated by the so-called software crisis. Ever since, the debate whether such a crisis exists has continued within the software engineering community. It is a crucial question,because if the answer is yes, software engineering may not be called an engineering discipline yet. If the answer were no, the question would be, what is it that constitutes this discipline.
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It turned out at the seminar that there may or may not be a software crisis, but there is definitely what might be called an identity crisis. A strong indicator for this phenomenon is the fact that after more than 30 years computer scientists are investigating the history of other established branches of engineering to find out what should be done to turn software engineering into a sound engineering discipline. In this endeavor, historians were regarded to be some kind of universal problem solvers who were called in whenever a general answer to some fundamental question was needed.
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Of course, this could not work, because history is not a methodical vehicle to clarify ones own identity or to derive normative principles and guidelines for a discipline. Furthermore, there is only little historic knowledge in the field of software engineering as compared to the"History of Programming Languages", for instance, or the history of electronic calculating devices. Thus, a seminar on the"History of Software Engineering"can only act as a starting point, providing a first overview of what has been accomplished so far and identify crucial issues to be studied in the future.
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1996年8月，大约有十几位历史学家与十几位计算机专家进行了会晤以讨论软件工程的历史。软件工程这个术语是作为1968年北大西洋公约组织软件工程会议争论的议题而特意命名的。此概念隐含的意思是：软件的生产应该以已有的传统工程分支中建立起来的理论基础和实践规程类型为基础。这一需求是由所谓的软件危机而引起的。从那以后，关于是否存在软件危机的争论在软件工程领域中就一直继续着。这是一个非常重要的问题，因为如果答案是肯定的，那么软件工程就还不能被称为工程学科；如果答案是否定的，那么这个问题将是：该学科到底是由什么构成的。
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该研讨会得出的结果是：软件危机或许存在，或许不存在，但一个可以称为特征危机的危机确实存在。这种现象的一个最强烈的表现是这样一个事实：在历经了30多年之后，计算机专家们仍在研究已建立起来的其他工程分支的历史，以发现应该做些什么才能把软件工程变成健全的工程学科。在这种努力中，历史学家们被认为是能够解决某种普遍问题的解决者，因此，无论什么时候，当重要问题需要一般的答案时，都要把他们召集起来。
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当然，这种做法并没有什么效果，因为历史并不是一个能阐明自己特征，或为一个学科导出规范原理或指导原则的井井有条的工具。此外，比如说，与程序设计语言历史或电子计算设备历史相比，软件工程领域的历史知识只是一点点。因此，一个关于"软件工程历史"的研讨会只能作为一个起点，为人们提供一个到目前为止都完成了哪些工作的概述以及指出将来要研究的重要议题是什么。
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What Does Software Engineering Do?
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Software engineering is the discipline of producing software to meet customer needs with the highest quality feasible given resource constraints. It is concerned with the ways in which people conduct their work activities and apply technology to produce and maintain software products and software-intensive systems. Issues of concern include specification, design, implementation,verification, validation, and evolution of software artifacts. Related topics include software metrics, project management, configuration management, quality assurance, peer reviews, risk management, and process improvement. Software engineering is essential for anyone working in development, maintenance, management, or related areas in a software organization.
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Software development currently suffers from 3 major deficiencies： (1) software engineering principles and practices, which should be the backbone of the software development life cycle are not fully accepted and followed by academia or industry； (2) straightforward, well established, and universally accepted design standards are lacking for the software development process and for representation of both process and product； and (3) the software development process is empirical in nature and not yet predicated on easily quantified and confirmed mathematical models. The effect of these and other deficiencies has been amplified by the rapid growth in the volume of software being produced and the almost exponential increase in the complexity of the problems now being solved with software. In spite of the need for a strongly structured approach to software's development, in many organizations software development is still basically a freestyle event.
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There may be other deficiencies in the software development process, the three that have been cited above are the root cause of many failed software developments. We cannot offer a"silver bullet", but we do, however, can offer the reader, interested in entering the software development field, a realistic preparation for the new software engineering environment.
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The overall objective of software engineering is to give the reader a sense of the flow of events in an integrated system and software development effort, and appreciation for and understanding of the software engineer's role in the system development process, and a comprehensive preparation for assuming responsibilities of a software engineer. We have also defined the following five fundamental objectives for the topic： (1) motivating readers with limited application experience by using realistic examples from recent experience and examining future directions for the discipline； (2) organizing and presenting material in such a way that the experienced practitioner will find it an accurate portrayal of the real world of software development； (3) developing a bridge from theory to practice in specific topics of interest to software engineers； (4) providing an algorithmic approach to each task or process carried out by a software engineer； and (5) providing a firm foundation upon which the reader can build.
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软件工程是在给定的资源条件下制作出满足用户需求的、可行的、高质量软件的学科。它是关于人们如何从事工作和利用技术来制作和维护软件产品和软件集成系统过程的方法。相关的议题包括：规格说明、设计、实现、测试、确认和软件产品的评价等。与上述论题相关的论题还有软件规格、项目管理、配置管理、质量保证、同行评价、风险管理以及过程完善。软件工程对从事开发、维护、管理或与软件机构相关领域的任何人而言都是极为重要的。
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软件开发目前有3个主要的不足：①作为软件开发生命周期支柱的软件工程原理和实践并没有被学术界或产业界普遍接受和遵循；②软件开发过程以及过程和产品的表达方式缺乏直接的、定义良好的和被普遍接受的设计标准；③软件开发过程本质上是经验主义的，还没有在容易量化和确认的数学模型上推断过。这些影响以及其他不足被软件产品的迅速增长和目前借助于软件求解问题的复杂性近乎指数式增长而扩大了。尽管软件开发需要一个强健的结构化方法，但在许多部门，软件开发基本上仍然是一个自由发挥的状况。
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软件开发过程中也许还有许多其他不足，但上述所讲的三个不足是软件开发失败的根本原因。我们不能提供一个"万全之策"，但我们确实能为对软件开发领域有兴趣的读者投入到新的软件工程环境中去提供一种实实在在的准备。
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软件工程的总体目标是使读者领悟一个集成系统和软件开发过程中的事件流程，体会并理解软件工程师在系统开发过程中的角色，为读者将来承担软件工程师的职责做好综合性的准备。我们还为该论题定义了如下5个基本目标：①通过最近做过的实际例子及仔细观察本学科未来的方向激发读者产生对自己有限经验进行应用的欲望；②用这样一种方法组织和表达资料的内容使有经验的专业人员感到它是真实的软件开发世界中的一种准确描述；③用软件工程师感兴趣的专门论题在理论与实践之间架起一座桥梁；④对软件工程师要完成的每项任务或过程都提供一个算法；⑤提供一个牢固的基础，并在此基础上发展。
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The world of multimedia is thriving with the growth of Internet and other new technologies, offering a range of new directions for people who just aren't satisfied with plain old text and images. But what exactly is multimedia? Multimedia has many definitions depending upon whom you ask. A standard definition follows： Multimedia is any combination of text, graphic art, sound, animation, and video delivered to you by computer or other electronic means.
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Multimedia has not been feasible until recently because computers have not been able to deliver an integrated package at an affordable price. In 1975 the first personal computers were marketed with low processor power, black and green text-only screens. By 1980 the addition of hard disk storage and simple graphics was seen. By 1987 we saw the capability to display color, more advanced graphics, sounds, and animation. In 1995 we have the capability to integrate digital video, sounds, animation and text into one hardware and software package. There is increasing emphasis on communications capabilities and sharing information over networks such as the Internet. Multimedia is made possible and affordable today because of increases in storage and speed and decreases in size and cost； this yields an increase in performance and availability.
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Interactivity is amount of control the user has over the presentation of information."Interactive multimedia"refers to multimedia that allows for user control. The three most common classifications of interactive are:
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（1） linear presentation: A linear presentation is one in which the author decides the sequence and manner in which information is presented. The user controls only the pace.
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（2） programmed branching program: A programmed branching program is one in which the user has some control over the sequence of presentation by selecting from a group of choices such as from a main menu. The author still maintains the control of deciding what to include in the choices available at any point in the program.
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（3） hypermedia: Hypermedia can be thought of as a web of interrelated information in whichthe user is in almost complete control of the pace, sequence and content of the presentation. Links provide for random access of information.
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多媒体世界随着国际互联网以及其他新技术的发展而不断兴旺，它为不满足于简单、陈旧的文本和图像的人们提供了一系列新的方向。但究竟什么是多媒体呢？多媒体有许多定义，这要看你是向谁提出这个问题。下面是一个标准的定义：多媒体是通过计算机或其他电子手段向你传送的文本、图形艺术、声音、动画与视频的任意组合。
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直到最近，当计算机能以可负担得起的价格传送一个集成程序包的时候，多媒体才成为可行的事情。1975年，最早的个人计算机在市场上出现，它们具有低速的处理器和黑绿色的纯文本屏幕。到1980年，增加了硬盘存储器和简单图形功能。到1987年，出现了能显示彩色、更高级的图形、声音和动画的功能。1995年，我们已经能把数值视频、声音、动画和文本集成到一个硬件和软件包上。人们在不断强调通信能力和对诸如国际互联网上的信息共享。由于存储容量和速度的增加以及尺寸和费用的减小，目前多媒体已可以实现并可以负担得起了，这就导致了性能和可用性的增加。
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交互性是用户控制呈现信息的程度。"交互式多媒体"是指允许用户控制的多媒体，三类最常见的交互是：
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（1）线性呈现：线性呈现是一种制作者可用来决定信息的呈现顺序和方式的呈现方式，用户只控制速度。
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（2）程控分支程序：程控分支程序是这样的程序——用户可以通过诸如主菜单那样的一组选择而对呈现次序进行某种控制，制作者仍然对程序中任何时刻要有哪些可用选项保持着控制。
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（3）超媒体：超媒体可被认为是相互关联的信息网，用户在这个网中几乎完全控制呈现的速度、次序和内容。链接提供了对信息的随机访问。
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The Definition of Computer Network
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There are many definitions of what the computer networks are. The definitions starting with phrase of the system of linked computers are misled because you could make a network without the linked computers. This network is characterized by people running back and forth between computers with floppy disks in their hands. Under this network, the computers are not linked physically but they still communicate data each other. Therefore, I would like to define it as follows： the computer network is the communication of data from one computer to one or more computers by any means such as people, wires, cables, or a telecommunications system.
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In the early 1980s, personal computer was developed with the concept of independent operation. With personal computer on your desktop, you could enter the information yourself, manipulate it, and produce the report you really wanted. While personal computer had become more powerful and applications for the computers included simple spreadsheet, databases, and word processors, the market for the computers exploded. So, many hardware and software venders joined in the market and it resulted competition.
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The competition pressed intense technological development, which led to increased power on the desktop and lower prices.Small businesses inDesktop computers were soon outperforming older, slowermainframe. Small businesses in particular were able to benefit from information management services that, a few years earlier, had been available only to wealthy corporations.
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For all its speed and power, the desktop computing environment had a difficulty in communicating among the users as computing information had became large and complicated.However, business information is useful only when it is communicated between human beings.The obvious solution was to link the desktop computers together. So, the idea of a Local Area Network (LAN) was developed.
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A local area network (LAN) is the communication of a number of computers by cable connecting to each one in a single location, usually a single floor of a building or all the computers in a small company. LANs may be contrasted with wide area networks (WANs). Stated simply, WANs are the communication between LANs by telephone lines leased from the various telephone companies, satellite links, packet radio, or microwave transceivers. The Internet has emerged as both the largest and the least expensive WAN in the world. Many companies take advantage of it now by forming private WANs, known as VPNs, or Virtual Private Networks, through encrypted communications over the Internet.
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对于计算机网络是什么有许多定义。因为没有连接的计算机你也可以建立一个网络，所以用连接的计算机的系统一词来定义会产生误解。这种网络可以被描述为手中拿着软盘的人们在计算机之间跑来跑去传递信息。在这种网络中，计算机之间物理上没有连接，但是它们仍然能够相互传递数据。因此，我喜欢这样定义网络：计算机网络就是可以通过任何一种方式，例如人、导线、电缆或电通信系统，在一台计算机与另一台或多台计算机之间进行的数据通信。
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在20世纪80年代初，个人计算机是依据独立操作的思想而开发的。通过桌面上的个人计算机，你可以自己输入信息、操纵它，并且生成你真正想要的报告。当个人计算机变得功能更强，并且计算机的应用开始包括简单的电子表格、数据库和字处理软件时，计算机市场开始蓬勃发展。因此，许多硬件和软件商加入计算机市场中，从而导致了竞争。
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竞争压力导致了技术的迅猛发展，从而导致了台式机功能的增强和价格的降低。台式机很快战胜了老式的、速度慢的大型机。特别是小型企业能够从信息管理服务中获益，而这种服务在几年前，只有有实力的公司才能获得。
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限于台式机的速度和功能，当计算信息变得大而复杂的时候，台式机计算环境在用户之间进行通信方面遇到了困难。然而，只有当商业信息在人们之间相互传递时，它才能起作用。一种显而易见的解决方法就是将多台台式机连接在一起。于是，局域网的思想就形成了。
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一个局域网（LAN）实现在某个单一区域中，通常是某个建筑物中的一层或者是一家小型公司的全部计算机，通过电缆彼此连接的多台计算机之间的数据通信。局域网可以与广域网（WAN）形成对比，简单地说，广域网就是通过从各电话公司租用的电话线、卫星链路、分组无线网以及微波收发装置，在各局域网之间进行通信。Internet已经成为世界上最大、最便宜的广域网。许多公司现在利用Internet构成被称作"虚拟专用网"（VPN）的专用广域网，在Internet上进行加密通信。
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What Does Network Administrator Do?
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Network administrator has full rights and permissions to all resources on a network. The administrator is usually responsible for installing, managing, and controlling servers and networking components. Administrators can also modify the properties of user accounts and the membership of groups, create and manage printers, install printers, share resources and assign permissions to those resources. Database administrator is responsible for programming and maintaining a large multi-relational database in a networked environment and facilitating direct access to the database by individuals on the network. Workgroup manager is responsible for solving problems, implementing standards and solutions, reviewing performance, and facilitating the efficiency of a specific group of individuals who are connected to larger network environment. Support staff is responsible for providing technical assistance to the system administrator in large complex network environments, and providing routine problem-solving and spot training to end-users. Maintenance contractor is responsible for hardware repairs and upgrades. Webmaster is responsible for implementing and maintaining the content and style of the company's Internet site, keeping the information accurate, up-to-date, and interesting.
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The development of network technology is continuous up to present. The benefits of computer network are as follows:
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.Sharing information: the computer can help you centralize the information and maintain control over it if you select one computer to store the shared information and have all other computers reference the information on that computer over the network.
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.Sharing hardware resources: a network allows anyone connected to the network to use printers, fax/modem, scanners, tape backup units or almost any other device that can be attached to a computer.
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.Sharing software resources: administrator can centrally install and configure the software and also restrict access to the software. It is easier than doing it on every one of the computers in an organization.
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.Preserving information: a network also allows for information to be backed up to a central location. It is difficult to maintain regular backups on a number of stand-alone computers so important information can be lost easily by mistake or by accident.
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.Protecting information: a network provides a more secure environment for a company's important information than stand-alone computers. Networks provide an additional layer of security by way of passwords.
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.Electronic-mail (E-mail): the computer network can also help people communicate by E-mail.You can attach electronic documents to mail message like photo, sound and video clip.
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网络管理员对一个网络上的所有资源拥有完全占有权和许可权。网络管理员通常负责安装、管理、控制服务器和网络组件。网络管理员还可以修改用户账号的属性、工作组的成员资格，创建和管理打印机、安装打印机，共享资源以及为那些资源分配权限。数据库管理员负责在一个网络环境中编程和维护一个大型的多关系型数据库，并且为个人在网络上直接访问数据库提供便利。工作组管理员负责解决问题、实现标准和解决方案、检查性能以及提高连接到一个更大的网络环境的特定的一组人员的效率。维护人员负责为在大型复杂的网络环境中工作的系统管理员提供技术帮助，为终端用户提供常规问题解答和现场培训。维修承包商负责对硬件的维修和升级。Web站点管理员负责实现和维护公司Internet站点的内容和风格，保证网站信息正确、及时、有趣。
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至今网络技术仍然在继续发展。计算机网络的优越性如下。
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.共享信息：如果你选择一台计算机存储要共享的信息，并且使其他的所有计算机能够通过网络访问这些信息，那么这台计算机就能帮助你集中管理信息和对它进行维护控制。
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.共享硬件资源：一个网络允许任何一位连接到这个网络的用户使用打印机、传真／调制解调器、扫描仪、磁带备份设备或者几乎所有能够连接到计算机上的其他设备。
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.共享软件资源：系统管理员能够集中安装和配置软件，还可以限制对软件的访问。这比在一个机构中的每台计算机上都做这些事情要容易得多。
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.保存信息：一个网络还允许将信息备份到一个集中的位置上。在大量的单独的计算机上维护常规备份是很困难的，因此重要信息很容易因错误或意外而丢失。
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.保护信息：一个网络比单机可以为一家公司的重要信息提供更加安全的环境。通过密码网络提供了一个附加的安全层。
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.电子邮件（E-mail）：计算机网络还能通过电子邮件来帮助人们进行通信。可以将诸如相片、声音和视频剪辑等电子文档附加在邮件信息上。
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The OSI reference model, sometimes also called ISO or 7 layers reference model for communication, has been developed by the International Standards Organization in early 1980's.Hence the interchangeable terms OSI/ISO Reference Model. This model describes the principles for interconnection of computer systems in an Open System Interconnection environment. So, it is an idealized model of the logical connections that must occur in order for network communication.Most protocol suites, such as TCP/IP, DECnet, and Systems Network Architecture (SNA), map loosely to the OSI reference model. The OSI model is not a protocol but it is good for understanding how various protocols within a protocol suite function and interact. But what does it really mean"Open System Interconnection"? The general principle which leads to the definition of the OSI standard was to allow connection and communication between any computer systems(from any vendors) as long as they comply with this"OPEN"standard.
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OSI参考模型，有时也称作ISO或者7层通信参考模型，是在20世纪80年代初由国际标准化组织开发的。因此，还可称作OSI/ISO参考模型。这个模型描述了在开放系统互联环境中计算机系统互联的若干原则。因此，它是一个适合于网络通信的理想的逻辑连接模型。许多协议簇，如TCP/IP、DECnet和系统网络体系结构（SNA），都不太严格地映射为OSI参考模型。OSI模型不是一个协议，但是它有助于理解一个协议簇中的各种协议是如何运行和相互作用的。"开放系统互接"真正意味着什么呢？OSI标准定义的总体原则是只要它们遵守这个"开放"标准，任何计算机系统（来源于任何厂商）之间都可以进行连接和通信。
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Most communication techniques have been developed and evolved for military purposes. The military has always put a priority on improving communication capabilities because of their strategic importance. Telegraph, telephone, radio and satellite were invented for the purpose of immediate and efficient communication in wartime. In a similar manner, we can also trace the origin of the Internet from defense purposes. The concept of the Internet was born in the Cold War period, due to the tension between the United States and the Soviet Union. The aim was to develop a decentralized network to keep critical information flowing in case of nuclear war.
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In the early 1960's the U.S. Department of Defense was concerned about the fact that the nation's communication networks could not withstand a nuclear attack from the Soviet Union. To surpass the Soviets in communication technology, the development of a new communication system was urgently required. RAND, which was the military sponsored research institute, suggested the concept of a network that would have no central control for the communication system. As a result, the Department of Defense's Advanced Projects Research Agency (DAPRA)commissioned some research institutes such as BBN (Bolt Beranek and Neumann Corp.) to develop the new communication system. This led to the birth of the first computer network system, called APRANET (Advanced Research Projects Agency Network). In 1969 the first IMPs was installed at UCLA and the initial communication was successful. This event implied the birth of one of the most revolutionary communication tools.
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大多数通信技术的开发和改进出于军事目的。由于通信方式在战略上起着重要的作用，因此军队总是优先改进通信能力。电报、电话、无线电和卫星是在战争期间为了快速、高效地进行通信而发明的。同样，我们追溯Internet的起源，它的出现也是出于国防目的。Internet的概念是在冷战期间被提出来的，源于美国和苏联之间的紧张局势。其目标是要开发一个非集中式的网络来保证在核战争的情况下传递重要信息。
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在20世纪60年代早期，美国国防部就在关注着一个事实——国家的通信网络不能抵御来自苏联的核攻击。为了要在通信技术方面超越苏联，急需开发一个新的通信系统。RAND，一个军事资助的研究学会，提出了一个在通信系统中没有中央控制的网络观念。结果，美国国防部高级计划研究署（DAPRA）委托一些研究机构（例如BBN Bolt Beranek和Neumann公司）开发了这个新的通信系统。这导致了第一个计算机网络系统的诞生，称作APRANET（高级计划研究署网）。在1969年，第一台集成微处理机被安装在加利福尼亚大学洛杉矶分校，而且首次通信就获得了成功。这一事件意味着一种最具革命性的通信工具的诞生。
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