Smell may take a while.（上面第二段最后一句）
Any teenager worth his or her salt is addicted to instant messaging. （上面的三段的第一句）“worth his or her salt ”
关于上面两句，有更好的译法么？

The next step beyond newspapers (plus magazines and scientific journals) is the on-line digital library. Many professional organizations, such as the ACM (www.acm.org) and the IEEE Computer Society (www.computer.org), already have many journals and conference proceedings on-line. Other groups are following rapidly. Depending on the cost, size, and weight of book-sized notebook computers, printed books may become obsolete. Skeptics should take note of the effect the printing press had on the medieval illuminated manuscript.
报纸（还有杂志和科学期刊）在线形式的下一步是在线的数字化图书馆。许多专业机构，如，ACM (www.acm.org)和IEEE计算机社区(www.computer.org)，已经有很多在线期刊和在线会议论文。其他一些团体也跟着迅速发展起来。凭借书本大小的笔记本电脑在成本、大小及重量方面的优势，打印的书籍将逐步被淘汰。对此持怀疑态度的人应该注意到，印刷机对于中世纪手抄业带来的影响其实也是与此类似的一种发展。

All of the above applications involve interactions between a person and a remote database full of information. The second broad category of network use is person-to-person communication, basically the 21st century's answer to the 19th century's telephone. E-mail is already used on a daily basis by millions of people all over the world and its use is growing rapidly. It already routinely contains audio and video as well as text and pictures. Smell may take a while.
以上提到的计算机网络的应用都涉及个人与富含信息资源的远程数据库之间的交互作用。计算机网络应用的第二大类是人与人之间的通信，基本上是用21世纪新的通信方式回应19世纪的电话。E－mail已经成为全世界数百万人每天基本的通信方式，并且它的使用将得到进一步的快速普及。电子邮件现在不仅有文本和图象，还有音频和视频。（下面再进一步介绍）

Any teenager worth his or her salt is addicted to instant messaging. This facility, derived from the UNIX talk program in use since around 1970, allows two people to type messages at each other in real time. A multiperson version of this idea is the chat room, in which a group of people can type messages for all to see.
青少年把他们的兴趣沉溺在即时消息（instant messaging）上面。这种便捷方式起源于1970年左右UNIX的talk 程序，它可以让两个人即时互发键入的消息。即时消息的多人互发方式是在一个聊天室（chat room）内，一组人都可以键入让所有人看到的消息。

Worldwide newsgroups, with discussions on every conceivable topic, are already commonplace among a select group of people, and this phenomenon will grow to include the population at large. These discussions, in which one person posts a message and all the other subscribers to the newsgroup can read it, run the gamut from humorous to impassioned. Unlike chat rooms, newsgroups are not real time and messages are saved so that when someone comes back from vacation, all messages that have been posted in the meanwhile are patiently waiting for reading.
全球范围内的新闻组，在选出的一群媒体人之间讨论每个想了解的话题，已经是很平常的事，并且这种现象得到进一步的普及。在这些讨论中，每个人都可以发送消息，所有其他订了改组新闻的用户都可以看到这些发送的消息，包括从幽默的小事到充满激情的大事，无所不及。与聊天室不同的是，新闻组的消息不是即时的，这些消息通常保存着以便一些人度假回来时可以来看看。所有的消息发送的同时也在耐心的等待它们的读者。

Another type of person-to-person communication often goes by the name of peer-to-peer communication, to distinguish it from the client-server model (Parameswaran et al., 2001). In this form, individuals who form a loose group can communicate with others in the group, as shown in Fig. 1-3. Every person can, in principle, communicate with one or more other people; there is no fixed division into clients and servers.
另外一种人际通信的方式通常称为对等交流，以区别于客户－服务器模型（Parameswaran et al., 2001）。在这种模式中，单独的个体形成松散的组，这些个体可以和其他的组进行交流，如图1-3所示。原则上，每个人可以和一个或多个人进行交流；这种模式下，客户和服务器没有固定的角色分类。

1.1.2 Home Applications家庭应用
In 1977, Ken Olsen was president of the Digital Equipment Corporation, then the number two computer vendor in the world (after IBM). When asked why Digital was not going after the personal computer market in a big way, he said: ''There is no reason for any individual to have a computer in his home.'' History showed otherwise and Digital no longer exists. Why do people buy computers for home use? Initially, for word processing and games, but in recent years that picture has changed radically. Probably the biggest reason now is for Internet access. Some of the more popular uses of the Internet for home users are as follows:
1. Access to remote information.
2. Person-to-person communication.
3. Interactive entertainment.
4. Electronic commerce.
1977年， Ken Olsen在DEC（Digital Equipment Corporation）当总裁。当时，这家公司是全球第二大计算机生产商（仅次于IBM）。当问及为什么DEC不大胆进军个人计算机市场时，他说，“没有理由让每个人在家里都有一台计算机。”然而历史证明，事实并不像他说的这样，而DEC如今也不复存在。为什么人们为了家用而购买计算机呢？最初的时候，是为了文字处理和游戏，但近年来，这种情况发生了很大变化。也许，现在最大的原因最主要的理由是可以访问Internet。对于家庭用户而言，Internet几个最流行的用途是：
¨ 访问远程信息
¨ 人际通信
¨ 交互式娱乐
¨ 电子商务

Access to remote information comes in many forms. It can be surfing the World Wide Web for information or just for fun. Information available includes the arts, business, cooking, government, health, history, hobbies, recreation, science, sports, travel, and many others. Fun comes in too many ways to mention, plus some ways that are better left unmentioned.
访问远程信息有很多种形式。可以浏览网页获取信息或者纯粹是上网娱乐。可利用的信息包括艺术、商业、烹饪、行政管理、健康、历史、业余爱好、娱乐消遣、科学、运动、旅游及其他一些信息。通过Internet进行娱乐的方式有很多是可以提及的，也有一些最好是不提为妙。

Many newspapers have gone on-line and can be personalized. For example, it is sometimes possible to tell a newspaper that you want everything about corrupt politicians, big fires, scandals involving celebrities, and epidemics, but no football, thank you. Sometimes it is even possible to have the selected articles downloaded to your hard disk while you sleep or printed on your printer just before breakfast. As this trend continues, it will cause massive unemployment among 12-year-old paperboys, but newspapers like it because distribution has always been the weakest link in the whole production chain.
很多报纸有了在线的版本，并且可以个性化。例如，有些时候，有可能告诉一家报纸你需要关于政治腐败、大型火灾、有关名人的丑闻、流行病的信息、而不要足球信息。有时，甚至可能在你睡觉的时候，这些被选出来的文章（自动）下载到硬盘上或者早餐前用打印机打印出来。随着这种趋势的发展，会使得大量12岁的报童失业，然而，报社喜欢这样，因为发行在整个生产链中已经成了最弱的一环。

看了几天潘老师翻译的计算机网络第四版，里面意译并不多。在这几天的翻译过程中，遇到一些复杂的句子结构不知道怎么用中文表达出来，看了潘老师翻译的之后才豁然开朗。主要还是要抓住句子之间的修饰关系，指代关系，抓住原作者要表达的涵义，然后用符合汉语习惯的表达方法表示出来。

有几个难句，当时怎么想都想不出，但是抓住几个关系之后发现并不难。

computer network    计算机网络

interconnected      相互连接的（互联）

the Internet        互联网

the World Wide Web  万维网

a distributed system 分布式系统

middleware           中间级

a remote machine     远程计算机

monitor production   监视生产过程

correlate            关联

resource share       资源共享

physical location    地理位置

physical resource    物理资源

  CD burners CD刻录机（播放机）

accounts receivable , financial statement应收帐款、财务报表

database              数据库

tyranny of geography 地理位置的束缚

  access                                访问
server               服务器

spreadsheet          电子表格

client               客户

arrangement          结构

client-server model  客户－服务模型

client process       客户进程

server process       服务器进程

perform执行

communication medium 通信媒介

a common gripe around the water cooler这样带来的一个问题是？？

improved communication 新型通信

Airlines, bookstores, music vendors航空公司、书店、音乐零售商

electronic commerce 电子商务

virtual             虚拟的

cooperation         协同

videoconference     视频会议

electronic mai                    l 电子邮件
前两天接了一个项目，做了之后发现速度快多了，感觉只有真正做起来才会更加注意翻译过程中的用词，中英文的不同表达方式，等等。


For smaller companies, all the computers are likely to be in a single office or perhaps a single building, but for larger ones, the computers and employees may be scattered over dozens of offices and plants in many countries. Nevertheless, a sales person in New York might sometimes need access to a product inventory database in Singapore. In other words, the mere fact that a user happens to be 15,000 km away from his data should not prevent him from using the data as though they were local. This goal may be summarized by saying that it is an attempt to end the ''tyranny of geography.''
就一些小公司而言，所有的计算机可能放在一间办公室或者在一栋楼里；但对大公司来说，计算机和员工可能分散在不同国家的几十个办公室或工厂里。然而，纽约的销售人员有时需要进入到新加坡的产品库存数据库。换句话说，如果用户只是离数据15,000km，这并不能阻止他使用这些数据，就好像这些数据存放在本地一样。计算机网络的这个目标可以概括为打破“地理位置的束缚（tyranny of geography）”。

In the simplest of terms, one can imagine a company's information system as consisting of one or more databases and some number of employees who need to access（访问） them remotely. In this model, the data are stored on powerful computers called servers. Often these are centrally housed and maintained by a system administrator. In contrast, the employees have simpler machines, called clients, on their desks, with which they access remote data, for example, to include in spreadsheets they are constructing. (Sometimes we will refer to the human user of the client machine as the ''client,'' but it should be clear from the context whether we mean the computer or its user.) The client and server machines are connected by a network, as illustrated in Fig. 1-1. Note that we have shown the network as a simple oval, without any detail. We will use this form when we mean a network in the abstract sense. When more detail is required, it will be provided.
用最简单的术语，你可以把一个公司的信息系统想象成由一个或多个数据库及一些需要远程获得这些数据的员工组成的。在这种模式下，数据储存在性能较大的计算机内，称为服务器（server）。通常，这些数据位于同一个场所，由系统管理员维护。相应地，在员工的桌上，是相对简单的机器，称作客户（client）。通过这些客户，员工可以访问远程数据，例如，远程访问包括他们建立的电子表格在内的一些数据（有时，我们会把客户计算机的用户看作“客户”，但必须弄清楚所在的语境，客户到底是指计算机还是计算机的使用者）。客户和服务器通过网络联系在一起，如图1-1所示。需要注意的是，我们把网络示意成一个简单的椭圆形，没有详细的列出一些具体的细节。当我们把网络看作是抽象意义的网络时，我们用这种形式来表达。当有需要的时候，我们也会提供更详细的说明。

This whole arrangement is called the client-server model. It is widely used and forms the basis of much network usage. It is applicable when the client and server are both in the same building (e.g., belong to the same company), but also when they are far apart. For example, when a person at home accesses a page on the World Wide Web, the same model is employed, with the remote Web server being the server and the user's personal computer being the client. Under most conditions, one server can handle a large number of clients.
这整个的结构称作客户－服务模型(client-server model)。这种模型如今已被广泛应用，并成为许多网络应用的基础。当客户和服务器在同一栋楼里（比如，同在一个公司），或离得很远时，都可以用客户-服务模型。例如，一个人在家登入万维网时，就是使用这种模型，其中，远程的网页服务器是该模型中的服务器，而用户的个人电脑是该模型中的客户。在大多数情况下，一台服务器可以处理大批量的客户数据。

If we look at the client-server model in detail, we see that two processes are involved, one on the client machine and one on the server machine. Communication takes the form of the client process sending a message over the network to the server process. The client process then waits for a reply message. When the server process gets the request, it performs the requested work or looks up the requested data and sends back a reply. These messages are shown in Fig. 1-2.
如果我们仔细审视客户－服务模式，会发现这里实际上包含两个过程，一个位于客户机器上的，一个位于服务器上的。其中的通信形式是这样的，客户进程通过网络将一个消息发送给服务器进程。然后，客户进程等待回复消息。当服务器进程得到请求消息之后，便执行所请求的工作或者检查客户所需要的数据，发送应答消息。这些消息如图1-2所示。
A second goal of setting up a computer network has to do with people rather than information or even computers. A computer network can provide a powerful communication medium among employees. Virtually every company that has two or more computers now has e-mail (electronic mail), which employees generally use for a great deal of daily communication. In fact, a common gripe around the water cooler is how much e-mail everyone has to deal with, much of it meaningless because bosses have discovered that they can send the same (often content-free) message to all their subordinates at the push of a button.
建立计算机网络的第二个目标是为了满足人的需要，而不是心细或计算机的需要。一个计算机网络可以在员工间提供强大的通信媒介（communication medium）。实际上，每个公司都有两台或者多台计算机有电子邮件(electronic mail，E-mail),员工通常用电子邮件来处理大量日常交流信息。事实上，这样带来的一个问题是，每人要处理大量邮件，而这些邮件大部分是无意义的，因为老板们发现他们按一下键，便可以将同样的信息（通常是无内容的）发送给所有的下属。

But e-mail is not the only form of improved communication made possible by computer networks. With a network, it is easy for two or more people who work far apart to write a report together. When one worker makes a change to an online document, the others can see the change immediately, instead of waiting several days for a letter. Such a speedup makes cooperation among far-flung groups of people easy where it previously had been impossible.
然而，e-mail并不是计算机网络带来的新型通信的唯一形式。有了计算机网络，两个或几个相距较远的人可以一同写同一个报告，这是非常容易做到的。当其中一人对在线文档做修改时，其他人即可看到他所做的修改，而不用花好几天时间等一封信件。这种快捷处理方式使相隔很远工作组之间的协同工作变得非常容易，这在以前来说，根本就不可能。

Yet another form of computer-assisted communication is videoconferencing. Using this technology, employees at distant locations can hold a meeting, seeing and hearing each other and even writing on a shared virtual blackboard. Videoconferencing is a powerful tool for eliminating the cost and time previously devoted to travel. It is sometimes said that communication and transportation are having a race, and whichever wins will make the other obsolete.
还有一种计算机辅助通信的模式，即视频会议。通过使用这项技术，异地员工可以一起开会，听到对方的声音，看到对方的样子，甚至在共享的一块虚拟黑板上写字。视频会议是一个功能强大的工具，可以降低成本，节约以前花在路上的时间。人们常说，通信和运输在进行一场竞争，不管那一方赢了，另一方都要被被淘汰。

A third goal for increasingly many companies is doing business electronically with other companies, especially suppliers and customers. For example, manufacturers of automobiles, aircraft, and computers, among others, buy subsystems from a variety of suppliers and then assemble the parts. Using computer networks, manufacturers can place orders electronically as needed. Being able to place orders in real time (i.e., as needed) reduces the need for large inventories and enhances efficiency.
建立计算机网络的第三个目标是为日渐增多的公司提供与其他公司之间的电子化服务，特别是供应商和客户之间的服务。例如，汽车、飞机、计算机的生产商或其他一些生产商，从不同的供应商处购买子系统，再将这些部件装配起来。通过使用计算机网络，生产商可以电子化定购其所需要的产品。及时定购（即根据需要）能减少大量库存，提高效率。

A fourth goal that is starting to become more important is doing business with consumers over the Internet. Airlines, bookstores, and music vendors have discovered that many customers like the convenience of shopping from home. Consequently, many companies provide catalogs of their goods and services online and take orders on-line. This sector is expected to grow quickly in the future. It is called e-commerce (electronic commerce).
第四个目标是，也即现在变得越来越重要的是，与客户通过因特网开展业务。航空公司、书店、音乐零售商发现许多客户喜欢在家购物的便捷模式，很多公司在线提供货物及服务的目录，并可以在线定购。计算机网络的这种用途有望在将来得到进一步的发展。这种模式称作电子商务（electronic commerce；e-commerce）。

注：今天时间不多，所以没来得及对潘老师的翻译，在此作为交流，勿仿！
1.1 Uses of Computer Networks

Before we start to examine the technical issues in detail, it is worth devoting some time to pointing out why people are interested in computer networks and what they can be used for. After all, if nobody were interested in computer networks, few of them would be built. We will start with traditional uses at companies and for individuals and then move on to recent developments regarding mobile users and home networking.

1.1计算机网络的使用15.30

在我们详细探讨技术问题之前，有必要花点时间来解释，为什么人们对计算机网络有着浓厚的兴趣，计算机网络可以用来做些什么。毕竟，如果没有人对计算机网络感兴趣，这门学科也很难建立起来。首先，我们将介绍计算机网络在公司及对个人的传统用法；然后，介绍在移动用户及家庭网络方面近来的发展。

1.1.1 Business Applications

Many companies have a substantial number of computers. For example, a company may have separate computers to monitor production, keep track of inventories, and do the payroll. Initially, each of these computers may have worked in isolation from the others, but at some point, management may have decided to connect them to be able to extract and correlate information about the entire company.

1.1.1商业软件

许多公司拥有很大数量的计算机。例如，一家公司已经把计算机分配到控制生产，跟踪库存及计算薪资等不同的职能中。最初，每台计算机可能执行与其他计算机不同的功能，但是在某些方面，出于管理的需要，必须把他们连接起来从中提取对整个公司有用的信息，并使这些信息相互关联。

Put in slightly more general form, the issue here is resource sharing, and the goal is to make all programs, equipment, and especially data available to anyone on the network without regard to the physical location of the resource and the user. An obvious and widespread example is having a group of office workers share a common printer. None of the individuals really needs a private printer, and a high-volume networked printer is often cheaper, faster, and easier to maintain than a large collection of individual printers.

把它看作更为一般的形式，这里的问题即是如何实现资源共享，目标是使所有的程序，设备，特别是数据能为网络上所有人所用。资源共享的一个很明显且大家所熟知的例子是共享打印机，办公室里的所有员工共用一台打印机。单个人确实没必要用私人打印机。通常，一台大容量网络打印机比一大群的个人打印机价格上更便宜，速度更快，也更容易维护。

However, probably even more important than sharing physical resources such as printers, scanners, and CD burners, is sharing information. Every large and medium-sized company and many small companies are vitally dependent on computerized information. Most companies have customer records, inventories, accounts receivable, financial statements, tax information, and much more online. If all of its computers went down, a bank could not last more than five minutes. A modern manufacturing plant, with a computer-controlled assembly line, would not last even that long. Even a small travel agency or three-person law firm is now highly dependent on computer networks for allowing employees to access relevant information and documents instantly.

然而，比共享诸如打印机、扫描仪和CD播放器等设备资源更重要的也许是信息共享。每家大型和中型企业及许多小公司在很大程度上依赖于计算机化的信息。大部分公司有客户记录、库存状态、应收帐款、财务报表、税收信息及其他更多的联网信息。假如所有的计算机停止工作，银行不到五分钟就会倒闭；而即使是一家拥有计算机控制生产线的现代制造型工厂，也不会持续太长时间。如今，甚至一家小旅行社或者三个人的法律公司也高度依赖计算机网络，以使员工快速获得相关信息和文件。

For smaller companies, all the computers are likely to be in a single office or perhaps a single building, but for larger ones, the computers and employees may be scattered over dozens of offices and plants in many countries. Nevertheless, a sales person in New York might sometimes need access to a product inventory database in Singapore. In other words, the mere fact that a user happens to be 15,000 km away from his data should not prevent him from using the data as though they were local. This goal may be summarized by saying that it is an attempt to end the ''tyranny of geography.''

就一些小公司而言，所有的计算机可能放在一间办公室或者在一栋楼里；但对大公司来说，计算机和员工可能分散在许多国家的几十个办公室或工厂里。

Although the computer industry is still young compared to other industries (e.g., automobiles and air transportation), computers have made spectacular progress in a short time. During the first two decades of their existence, computer systems were highly centralized, usually within a single large room. Not infrequently, this room had glass walls, through which visitors could gawk at the great electronic wonder inside. A medium-sized company or university might have had one or two computers, while large institutions had at most a few dozen. The idea that within twenty years equally powerful computers smaller than postage stamps would be mass produced by the millions was pure science fiction.

与汽车、航空运输等其他行业相比，尽管计算机仍是朝阳产业，但是在短短的时间内却取得了惊人的进展。在头二十年的发展过程中，计算机系统高度集中化，通常在一个很大的房间内。一般这个房间有玻璃墙，透过玻璃墙，参观的人会被其中巨大奇异的电子设备所吸引。中等企业或是大学可能拥有一两台计算机，而大型的研究院最多几十台。在二十年里，让数百万的企业大规模生产比邮票还小的强大计算机的想法纯粹是科学幻想。（要在二十年内生产出大量同样功能但体积比邮票还小的计算机，在当时的人们看来纯属科学幻想）（虚拟！）

The merging of computers and communications has had a profound influence on the way computer systems are organized. The concept of the ''computer center'' as a room with a large computer to which users bring their work for processing is now totally obsolete. The old model of a single computer serving all of the organization's computational needs has been replaced by one in which a large number of separate but interconnected computers do the job. These systems are called computer networks. The design and organization of these networks are the subjects of this book.

计算机和通信的融合已经对计算机系统的组织方式产生了深远的影响。以前人们心中“计算机中心”的概念已完全过时了，即用户带着他们的任务到一间放大型计算机的房间内处理。那种由一台计算机为所有机构的计算需要提供服务的旧模式已经被大量独立而又相互联系的计算机所取代。这些系统就是计算机网络。而这些网络的设计和组织便是该书的主要内容。

Throughout the book we will use the term ''computer network'' to mean a collection of autonomous computers interconnected by a single technology. Two computers are said to be interconnected if they are able to exchange information. The connection need not be via a copper wire; fiber optics, microwaves, infrared, and communication satellites can also be used. Networks come in many sizes, shapes and forms, as we will see later. Although it may sound strange to some people, neither the Internet nor the World Wide Web is a computer network. By the end of this book, it should be clear why. The quick answer is: the Internet is not a single network but a network of networks and the Web is a distributed system that runs on top of the Internet.

书中，我们将用术语“计算机网络”来表示由一种技术相互联系起来的自主计算机的集合。两台计算机如果能相互交换信息，称作互联。这种连接不需要通过铜线；光纤，微波，红外线和通信卫星等都可以用来建立连接。后面我们可以看到，网络可以有不同的大小，形状，形式。尽管对很多人来说比较陌生，互联网和万维网都不是计算机网络（可能很多人对此会觉得很奇怪）。在本书的结尾部分，我们将详细阐述其原因。概言之（现在给出一个简单的答案），互联网不是单一的网络，而是许多网络联系在一起构成的一个网络；万维网是在互联网之上运行的分布式系统。

There is considerable confusion in the literature between a computer network and a distributed system. The key distinction is that in a distributed system, a collection of independent computers appears to its users as a single coherent system. Usually, it has a single model or paradigm that it presents to the users. Often a layer of software on top of the operating system, called middleware, is responsible for implementing this model. A well-known example of a distributed system is the World Wide Web, in which everything looks like a document (Web page).

在一些文献中，计算机网络和分布式系统是比较容易混淆的概念。他们的主要区别在于，分布式系统中，相互独立的计算机组合对用户来说是一个单一的关联系统。（在一个分布式系统中，一组独立的计算机展现给用户的是一个统一的整体，就好像一个系统似的）通常，呈现给用户的只有一个模式或者范例。位于操作系统之上的一层软件称作中间件（middleware），负责实施该模式。分布式系统的一个众所周知的例子是万维网，即在万维网中，所有的内容看上去像文档（网页）一样。

In a computer network, this coherence, model, and software are absent. Users are exposed to the actual machines, without any attempt by the system to make the machines look and act in a coherent way. If the machines have different hardware and different operating systems, that is fully visible to the users. If a user wants to run a program on a remote machine, he [ ] has to log onto that machine and run it there.

[ ] ''He'' should be read as ''he or she'' throughout this book.

 在计算机网络中，这种关联、模式和软件都是不存在的。用户面对的是实实在在的机器，而不能通过系统使机器的样子和行为一致。如果机器有不同的硬件和操作系统，那么这些差异对用户来说是完全可见的。如果用户想运行一台远程计算机上的程序，他可以登录到那台机器并运行程序。（本书中，他可以看作“他”或“她”）

In effect, a distributed system is a software system built on top of a network. The software gives it a high degree of cohesiveness and transparency. Thus, the distinction between a network and a distributed system lies with the software (especially the operating system), rather than with the hardware.

实际上，分布式系统是建立在网络之上的软件系统。该软件提供了高度的粘聚性和透明度。因此，网络与分布式系统之间的区别在于软件（特别是操作系统），而不是硬件。

Nevertheless, there is considerable overlap between the two subjects. For example, both distributed systems and computer networks need to move files around. The difference lies in who invokes the movement, the system or the user. Although this book primarily focuses on networks, many of the topics are also important in distributed systems. For more information about distributed systems, see (Tanenbaum and Van Steen, 2002).
尽管如此，分布式系统和计算机网络之间还是有很多重叠的地方。比如，他们都需要移动文档。差异在于谁发起的移动，是系统还是用户。虽然本书大部分在关注网络，但在分布式系统中，许多主题同样非常重要。关于分布式系统的更多信息，请参看 Tanenbaum and Van Steen, 2002 。

Chapter 1. Introduction

 

第一章 概述

Each of the past three centuries has been dominated by a single technology. The 18th century was the era of the great mechanical systems accompanying the Industrial Revolution. The 19th century was the age of the steam engine. During the 20th century, the key technology was information gathering, processing, and distribution. Among other developments, we saw the installation of worldwide telephone networks, the invention of radio and television, the birth and unprecedented growth of the computer industry, and the launching of communication satellites.

在过去的三个世纪中，每个世纪都有一种占主导地位的技术。18世纪伴随工业革命的到来，开辟了大机器系统的纪元。19世纪是蒸气机时代。20世纪（在20世纪的发展过程中），主要的技术是信息收集、加工及分类。在这个时代的其他一些发展中，我们看到世界范围内电话网络的安装，无线电广播及电视的发明，计算机产业的诞生及空前发展，还有通信卫星的发射。

As a result of rapid technological progress, these areas are rapidly converging and the differences between collecting, transporting, storing, and processing information are quickly disappearing. Organizations with hundreds of offices spread over a wide geographical area routinely expect to be able to examine the current status of even their most remote outpost at the push of a button. As our ability to gather, process, and distribute information grows, the demand for ever more sophisticated information processing grows even faster.
随着技术的快速发展（作为技术快速发展的一个直接结果是） ，这些领域迅速融合，信息采集、存贮及处理之间的差异很快消失（正在很快消失）。对于具有数百个办公室的大型组织来说，尽管这些办公室分布在广阔的地理区域中，但未来期望的情景是，工作人员只需单击一下按钮，就可查到最远处发布的状态随着我们信息收集、加工及分类能力的增长，这种对更为复杂的信息加工的永久需求得到更快的增长。