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[单选题]
Wide Area Network代表的广域网，简写为（)。
A.WOA
B.WAN
C.LAN
D.NAW
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A.WOA
B.WAN
C.LAN
D.NAW
答案
更多“Wide Area Network代表的广域网，简写为()。”相关的问题
第1题
A.public
B.private
C.local area
D.wide area
第2题
从供选择的答案中选出应填入下面一段英文中______内的正确答案。
A brouter is a network bridge and a router combined in a single product. A bridge is a device that connects one local area network (LAN) to(1)local area network that uses the same protocol (for example,(2)or Token Ring). If a data unit on one LAN is intended for a(3)on an interconnected LAN, the bridge forwards the data unit to that LAN; otherwise, it passes it along on the same(4). A bridge usually offers only one path to a given interconnected LAN. A router connects a network to one or more other(5)that are usually part of a wide area network (WAN) and may(6)a number of paths out to destinations on those networks. A router therefore needs to have(7)information than a bridge about the interconnected networks. It(8)a routing table for this information. Since a given outgoing data unit or packet from a computer may be intended for an(9)on the local network, on an interconneted LAN, or the wide area network, it makes sense to have a single unit that(10)all data units and forwards them appropriately.
供选择的答案：
1．more 2．LAN 3．Ethernet 4．address 5． offer
6．destination 7．consults 8．another 9．networks 10．examines
第3题
选出应填入下面一段英语中______内的正确答案。
Asynchronous Transfer Mode (ATM)is a(1)that promises to change the fabric of local and wide area communications.
The key advantage of ATM is the capability to move voice, data, graphics and(2)at speeds ofup to 2 gigabits per second.
At ATM switch allows you to create a(3)network that is completely independent from the(4)configuration ofthe network.
ATM uses a(5)called cell switching to convert data into fixed length cells of 53 bytes each, so they can be switched very quickly and efficiently.
供选择的答案：
(1) technology (2) techniques (3) technique (4) method
(5) methods (6) logical (7) local (8) wide
(9) physical (10) program (11) characters (12) video images
第5题
A.Router(config)#router ospf 1
B.Router(config)#router ospf 0
C.Router(config)#router ospf area 0
D.Router(config-router)#network 192.168.16.0 0.0.0.255 area 0
E.Router(config-router)#network 192.168.16.0 0.0.0.255 0
F.Router(config-router)#network 192.168.16.0 255.255.255.0 area 0
第6题
A.VLAN 的全称虚拟局域网 Vitual Local AREA Network
B.VLAN 的全称是 Access Network
C.VLAN 隔离了冲突域
D.VLAN 之间可以互通
第7题
A recent development is the local area network (LAN).【21】its name implies, it【22】a local area—possibly as small as a single room, typically an area like an university campus or the premises of a particular business. Local area networks were developed to【23】a need specific to microcomputers—the sharing of expensive resources. Microcomputers are cheap,【24】highcapacity disc stores, fast and/or good quality printers, etc. are expensive. The object of the LAN is to allow【25】microcomputers shared access to these expensive resources. Since the microcomputers are【26】, it is a necessary feature of a LAN that the method of connection to the network, and the network hardware【27】, must also be cheap.
A local area network links a number of computers and a number of sewers【28】provide communal facilities, e. g. file storage. (A server usually includes a small microprocessor for control purposes.) The computers and servers are known【29】stations. There are two methods of【30】in common use, tings and broadcast networks.
In the ring method(often called a Cambridge Ring)all the stations are linked in a ring,【31】includes one special station, the monitor station.
In broadcast networks, all the stations are【32】to a single linear cable (usually co-ax cable), and any transmission will be received by all stations.
【33】technology is used, local area networks are a development of the greatest importance.【34】as programming is simplified by an approach that thinks in terms of small procedures or programs, each doing a well-defined job, the computer system of tomorrow is likely to be【35】lots of small systems, each doing a specific job, linked by a local area network.
(41)
A．As
B．Like
C．Since
D．Because
第8题
Networks and Application
网络及应用
Each of the past three centuries has been dominated by a single technology. The 18th Century was the time of the great mechanical systems accompanying the Industrial Revolution[1]. The 19th Century was the age of the steam engine. During the 20th Century, the key technology has been information gathering, processing, and distribution. Among other developments, we have seen 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.
Due to 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 even more sophisticated information processing grows even faster.
Although the computer industry is 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-size company or university might have had one or two computers, while large institutions had at most a few dozen. The idea that within 20 years equally powerful computers smaller than postage stamps would be mass produced by the millions was pure science fiction.
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 term "computer network" means an interconnected collection of autonomous computers. 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, microwave, and communication satellites can also be used. By requiring the computers to be autonomous, we wish to exclude from our definition systems in which there is a clear master/slave relation. If one computer can forcibly start, stop, or control another one, the computers are not autonomous. A system with one control unit and many slaves is not a network; nor is a large computer with remote printers and terminals.
There is considerable confusion in the literature between a computer network and a distributed system. The key distinction is that in a distributed system the existence of multiple autonomous computers is transparent to the user. He can type a command to run a program, and it runs. It is up to the operating system to select the best processor, find and transport all the input files to that processor, and put the results in the appropriate place.
In other words, the user of a distributed system is not aware that there are multiple processors; it looks like a virtual uniprocessor. Allocation of jobs to processors and files to disks, movement of files between where they are stored and where they are needed, and all other system functions must be automatic.
With a network, users must explicitly log onto one machine, explicitly submit jobs remotely, explicitly move files around and generally handle all the network management personally. With a distributed system, nothing has to be done explicitly; it is all automatically done by the system without the users' knowledge.
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. 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 and so forth.
Networks for Companies
Many organizations have a substantial number of computers in operation, often located far apart. For example, a company with many factories may have a computer at each location to keep track of inventories, monitor productivity, and do the local 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.
Put in slightly more general form[2], 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. In other words, the mere fact that a user happens to be 1,000 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. "
A second goal is to provide high reliability by having alternative sources of supply. For example, all files could be replicated on two or three machines, so if one of them is unavailable (due to a hardware failure), the other copies could be used. In addition, the presence of multiple CPUs means that if one goes down, the others may be able to take over its work, although at reduced performance. For military, banking, air traffic control, nuclear reactor safety, and many other applications, the ability to continue operating in the face of hardware problems is of utmost importance.
Another goal is saving money. Small computers have a much better price/performance ratio than large ones. Mainframes (room-size computers) are roughly a factor of ten faster than personal computers, but they cost a thousand times more. This imbalance has caused many system designers to build systems consisting of personal computers, one per user, with data kept on one or more shared file server machines. In this model, the users are called clients, and the whole arrangement is called the client-server model[3]. It is illustrated in Fig. 1.
In the client-server model, communication generally takes the form of a request message from the client to the server asking for some work to be done. The server then does the work and sends back the reply. Usually, there are many clients using a small number of servers.
Another networking goal is scalability, the ability to increase system performance gradually as the workload grows just by adding more processors. With centralized mainframes, when the system is full, it must be replaced by a larger one, usually at great expense and even greater disruption to the users. With the client-server model, new clients and new servers can be added as needed.
Yet another goal of setting up a computer network has little to do with technology at all. A computer network can provide a powerful communication medium among widely separated employees. Using a network, it is easy for two or more people who live far apart to write a report together. When one worker makes a change to an on-line 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. In the long run, the use of networks to enhance human-to-human communication will probably prove more important than technical goals such as improved reliability.
Networks for People
The motivations given above for building computer networks are all essentially economic and technological in nature. If sufficiently large and powerful mainframes were available at acceptable prices, most companies would simply choose to keep all their data on them and give employees terminals connected to them. In the 1970s and early 1980s, most companies operated this way. Computer networks only became popular when networks of personal computers offered a huge price/performance advantage over mainframes.
Starting in the 1990s, computer networks began to start delivering services to private individuals at home. Below we will sketch three of the more exciting ones that are starting to happen:
1. Access to remote information.
2. Person-to-person communication.
3. Interactive entertainment.
Access to remote information will come in many forms. One area in which it is already happening is access to financial institutions. Many people pay their bills, manage their bank accounts, and handle their investments electronically. Home shopping is also becoming popular, with the ability to inspect the on-line catalogs of thousands of companies. Some of these catalogs will soon provide the ability to get an instant video on any product by just clicking on the product's name.
Newspapers will go on-line and be personalized. It will be possible to tell the newspaper that you want everything about corrupt politicians, big fires, scandals involving celebrities, and epidemics, but no football, thank you; At night while you sleep, the newspaper will be downloaded to your computer's disk or printed on your laser printer. On a small scale, this service already exists. The next step beyond newspapers is the on-line digital library. 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.
Another application that falls in this category is access to information systems like the current World Wide Web, which contains information about the arts, business, cooking, government, health, history, hobbies, recreation, science, sports, travel, and too many other topics to even mention.
All of the above applications involve interactions between a person and a remote database. The second broad category of network use will be person-to-person interactions, basically the 2lst century's answer to the 19th century' s telephone. Electronic mail or email is already widely used by millions of people and will soon routinely contain audio and video as well as text. Smell in messages will take a bit longer to perfect.
Real-time email will allow remote users to communicate with no delay, possibly seeing and hearing each other as well. This technology makes it possible to have virtual meetings, called videoconference, among far-flung people. It is sometimes said that transportation and communication are having a race, and whichever wins will make the other obsolete. Virtual meetings could be used for remote school, getting medical opinions from distant specialists, and numerous other applications.
Worldwide newsgroups, with discussions on every conceivable topic are already commonplace among a select group of people, and this 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.
Our third category is entertainment, which is a huge and growing industry. The killer application[4]here (the one that may drive all the rest) is video on demand. A decade or so hence, it may be possible to select any movie or television program ever made, in any country, and have it displayed on your screen instantly. New films may become interactive, where the user is occasionally prompted for the story direction with alternative scenarios provided for all cases. Live television may also become interactive, with the audience participating in quiz shows, choosing among contestants, and so on.
On the other hand, maybe the killer application will not be video on demand. Maybe it will be game playing. Already we have multiperson real-time simulation games, like hide- and-seek in a virtuaI dungeon, and flight simulators with the players on one team trying to shoot down the players on the opposing team. If done with goggles and 3 dimensional real time, photographic-quality moving images, we have a kind of worldwide shared virtual reality.
In short, the ability to merge information, communication, and entertainment will surely give rise to a massive new'industry based on computer networking.
Notes
[1] Industrial Revolution:(18世纪60年代在英国开始的)产业革命，工业革命。
[2] put in slightly more general form: 用略微更广的形式来说。
[3] client-server model: 客户机 /服务器模式。
[4] the killer application: “杀手” (具有影响力的)应用程序 ,强有力或受欢迎的程序。
Choose the best answer for each of the following:
第9题
从供选择的答案中选出应填入下列英文语句中______内的正确答案。
PCs originated as stand-alone(1), however,in recent years many have been(2)to Local Area Networks (LANs). In a LAN, the data and usually the user application reside on the File Server, a PC running a special Network Operating System (NOS) such as Novell's NetWare or Microsoft's LAN Manager. The File Server manages the LAN users' shared access to data on its hard(3)and frequently provides access to other shared resources, such as printers. While a LAN enables users of PC-based databases to share(4)data files, it doesn't significantly change how the DBMS works; all the actual data(5)is still performed on the PC running the database application.
供选择的答案：
(1) calculating (2) common (3) connected (4) disks (5) displayed
(6) systems (7) printers (8) processing (9) some (10) workstations
第10题
Internet History
因特网史
Expanding on the freeway metaphor, with cars, there are various levels of knowledge; learning to drive is easy, and it is all you really need to know about cars. This is like learning to surf the Internet. In the course of driving, you learn about highways, shortcuts, and so on, and using the Web is very similar, that is, with practice, you will learn where and how to find things.
Also, in driving, you can go another step and learn how an engine works and how to do routine maintenance and repairs, such as oil changes and tune-ups. On the Web, the equivalent is to learn how Web pages are put together, which you have already started to do.
A still deeper level of involvement with cars is learning how to do complex repairs, or to design and build them. Not many people pursue cars to this stage. On the Web, a similar level of involvement is writing software, either building applets[1]in a language such as Java[2], or developing more general-purpose tools for others to use in navigating the Web. Again, only a limited number of people aspire to this level.
Today, the Information Superhighway is in place, but for many people, the mysteries surrounding it involve where to go and how to travel. Like traveling a highway in a foreign country and being unable to read the road signs, navigating the Information Superhighway can be frustrating and time-consuming without the right knowledge and tools.
Consider that there are many ways to travel sidewalks, roads, and freeways to get to where we want to go. We can take a bicycle, a bus, a car, or a pair of in-line skates. Similarly, there are many ways to use the Internet to send and retrieve information. These include, but are not limited to[3]: e-mail, file transfer, remote login, and the Web. New methods of using the Internet will probably be conceived and developed in the near future, and existing methods will be improved.
Internet History
The history of the Internet is best explained via a timeline. We have included events that were important and required innovation, as well as other interesting and related items. For each item mentioned on the timeline, we provide a brief synopsis. While the timeline begins in 1969, we present some general comments on the 1960s, for background. The history of the Internet is fascinating both for itself and as a case study of technological innovation.
Essential to the early Internet concept was packet switching[4], in which data to be transmitted was divided into small packets of information and labeled to identify the sender and recipient. The packets were sent over a network and then reassembled at their destination. If any packet did not arrive or was not intact, the original sender was requested to resend the packet. Prior to packet switching, the less efficient circuit switching method of data transmission was used. In the early 1960s, several papers on packet switching theory were written, laying the groundwork for computer networking as it exists today.
In 1969, Bolt, Beranek, and Newman, Inc., (BBN)[5]designed a network called the Advanced Research Projects Agency Network (ARPANET)[6]for the United Sates Department of Defense. The military created ARPANET to enable researchers to share "super-computing" power. It was rumored that the military developed the ARPANET in response to the threat of a nuclear attack destroying the country's communication system.
Initially, only four nodes (or hosts) comprised the ARPANET. They were located at the University of California at Los Angeles, the University of California at Santa Barbara, the University of Utah, and the Stanford Research Institute. The ARPANET later became known as the Internet.
In the 1970s, the ARPANET was used primarily by the military, some of the larger companies, such as IBM, and universities (for e-mail). The general population was not yet connected to the system and very few people were on-line at work.
The use of local area networks (LANs) became more prevalent during the 1970s. Also, the idea of an open architecture was promoted; that is, networks making up the ARPANET could have any design. In later years, this concept had a tremendous impact on the growth of the ARPANET.
By 1972, the ARPANET was international, with nodes in Europe at the University College in London, England, and the Royal Radar Establishment in Norway. The number of nodes on the network was up to 23, and the trend would be for that number to double every year from then on. Ray Tomlinson, who worked at BBN, invented e-mail.
In 1979 user Network (USENET) was started by using UUCP[7]to connect Duke University and the University of North Carolina at Chapel Hill. Newsgroups emerged from this early development.
In the 1980s, Transmission Control Protocol/lnternet Protocol (TCP/IP)[8], a set of rules governing how networks making up the ARPANET communicate, was established. For the first time, the term "Internet" was being used to describe the ARPANET. Security became a concern, as viruses appeared and electronic break-ins occurred.
The 1980s saw the Internet grow beyond being predominantly research oriented to including business applications and supporting a wide range of users. As the Internet became larger, the Domain Name System (DNS) was developed, to allow the network to expand more easily by assigning names to host computers in a distributed fashion.
The Computer Science Network (CSNET) connected all university computer science departments in the United States. Computer science departments were relatively new, and only a limited number existed in 1980. CSNET joined the ARPANET in 1981. Two years later the United States Defense Communications Agency required that TCP/IP be used for all ARPANET hosts. Since TCP/IP was distributed at no charge, the Internet became what is called an open system. This allowed the Internet to grow quickly, as all connected computers were now "speaking the same language. " Central administration was no longer necessary to run the network.
In 1985, the National Science Foundation Network (NSFNET)[9]was formed to connect the National Science Foundation's (NSF's) five super-computing centers. This allowed researchers to access the most powerful computers in the world, at a time when large, powerful, and expensive computers were a rarity and generally inaccessible.
The virus called Internet Worm[10](created by Robert Morris while he was a computer science graduate student at Cornell University) was released. It infected 10 percent of all Internet hosts. Also in this year, Internet Relay Chat(IRC)[11]was written by Jarkko Oikarinen.
NSF took over control of the ARPANET in 1989. This changeover went unnoticed by nearly all users. Also, the number of hosts on the Internet exceeded the 100,000 mark.
During the 1990s, lots of commercial organizations started getting on-line. This stimulated the growth of the Internet like never before. URLs[12]appeared on television advertisements and, for the first time, young children went on-line in significant numbers.
Graphical browsing tools were developed, and the programming language HTML[13]allowed users all over the world to publish on what was called the World Wide Web. Millions of people went on-line to work, shop, bank, and be entertained. The Internet played a much more significant role in society, as many non-technical users from all walks of life got involved with computers. Computer-literacy and Internet courses sprang up all over the country.
Gopher[14]was developed at the University of Minnesota, whose sports team's mascot is the Golden Gopher. Gopher allowed you to "go for" or fetch files on the Internet using a menu based system. Many gophers sprang up all over the country, and all types of information could be located on gopher servers. Gopher is still available and accessible through Web browsers, but its popularity has faded; for the most part, it is only of historical interest.
In 1991, the World Wide Web (WWW) was created as a simple way to publish information and make it available on the Internet. The interesting nature of the Web caused it to spread, and it became available to the public in 1992. Those who first used the system were immediately impressed.
Mosaic[15], a graphical browser for the Web, was released by Marc Andreessen and several other graduate students at the University of Illinois, the location of one of NSF's super-computing centers. Sometimes you will see Mosaic referred to as NCSA[16]Mosaic, where NCSA stands for the National Center for Supercomputing Applications. Mosaic was first released under X Windows and graphical UNIX[17]. To paraphrase a common idiom, each person who used the system loved it and "told five friends," and Mosaic's use spread rapidly.
The company called Netscape Communication, formed by Marc Andreessen and Jim Clark, released in 1994 Netscape Navigator, a Web browser that captured the imagination of everyone who used it. The number of users of this software grew at a phenomenal rate. Netseape made (and still makes) its money largely through advertising on its Web pages. And in the same year, Stanford graduate students David Filo and Jerry Yang developed their Internet search engine and directory called Yahoo, which is now world-famous. One year later, the Internet programming environment, Java, was released by Sun Microsystems, Inc. This language, originally called Oak, allowed programmers to develop Web pages that were more interactive.
The software giant, Microsoft, in 1995, committed many of its resources to developing its browser, Microsoft Internet Explorer, and Internet applications. Some of the first courses about the Internet were given in the meanwhile. Course development has been difficult, because of the rapidly changing software. In 1998, Netscape Communications released the source code for its Web browser.
Notes
[1] applets: 应用程序片段，小应用程序，用Java语言编写的一种应用程序。
[2] Java: Java语言。美国Sun公司的James Gosling于1990年编制的一种计算机语言，1995年首次公布，Java是在C++语言基础上发展起来，语法上与C++相似的一种面向对象的语言。
[3] These include, but are not limited to: 这些包括，但不限于……
[4] packet switching：(数据、信息)包交换法，(报文)分组交换技术(借助编址的报文分组选择路由并发送数据，以使一个信道只在包传送时才被占用的处理方法或技术)。
[5] Bolt, Beranek, and Newman, Inc.，(BBN)：BBN公司，美国马萨诸塞州的一个公司，早期维护ARPANET网，后来维护因特网的核心网关。
[6] the Advanced Research Projects Agency Network (ARPANET)：阿帕网，ARPA网(高级研究计划局的计算机网络名)。
[7] UUCP: Unix到Unix的拷贝程序(UNIX to UNIX Copy)。UUCP是Usenet用于数据传输的主要通讯协议之一。
[8] Transmission Control Protocol/lnternet Protocol (TCP/IP)：传输控制协议/网络协议。
[9] the National Science Foundation Network (NSFNET)：自然科学基金网。
[10] Internet Worm：因特网虫(1988年美国康奈尔大学的一个学生写的字符串自复制开玩笑程序，一夜之间遍布整个因特网，导致大多数计算机停止运行)。
[11] Internet Relay Chat(IRC)：因特网交谈服务系统(使用文本实时交谈，可多人参加)。
[12] URLs (Uniform Resource Locator)：统一资源地址、统一资源定位器(程序)。
[13] HTML(Hypertext Markup Language)：超文本链接标示语言。
[14] Gopher：跑腿鼹鼠，是用户在因特网上的个人图书管理员，供用户查询搜索所需的系统资源。
[15] Mosaic：1993年因特网上出现的第一个图形界面Web浏览器。
[16] NCSA (National Center for Supercomputing Application)：国家超级计算应用中心。
[17] Unix: 一种多用户的计算机操作系统。
Choose the best answer:
第11题
Computer Office System
计算机办公系统
Computer office systems are computers and their peripheral equipment is used to create, store, process, or communicate information in a business environment. This information can be electronically produced, duplicated, and transmitted.
The rapid growth of the service sector of the United States economy beginning in the mid 1970s has furnished a new market for sophisticated office automation. With the increasing incorporation of microchips and microcircuitry into office equipment[1], the line between the computer and other equipment has blurred.
At the same time, computers either stand alone or as part of a network and specialized software programs are taking over tasks such as facsimile transmission-or FAX, voice mail, and telecommunications that were once performed by separate pieces o.f equipment. In fact, the computer has virtually taken the place of typewriters, calculators, and manual accounting techniques and is rapidly taking over graphics design, production scheduling, and engineering design as well.
During the first half of the 20th century, financial and other numerical record keeping tasks were performed manually or by bookkeeping machines, billing machines, tabulating equipment, and other types of electromechanical accounting devices. In the 1950s, such machines were increasingly replaced by mainframe computers-large, very expensive, high speed machines that required trained operators as well as a special temperature regulated facility to prevent overheating. Use of these machines today is limited to large organizations with heavy volume data processing requirements. Time sharing, allowing more than one company to use the same mainframe for a fee, was instituted to divide the cost of the equipment among several users while ensuring that the equipment is utilized to the maximum extent.
Mainframes with remote terminals, each with its own monitor, became available in the mid 1970s and allowed for simultaneous input by many users. With the advent of the minicomputer, however, a far less expensive alternative became available. The transistor and microelectronics made manufacture of these smaller, less complex machines practicable. Minicomputers, the first of which entered general business use in the early 1960s, are now widespread in commerce and government. Terminals linked to the central processing unit (CPU) are under the direct control of the individual user rather than centralized staff. In recent years, however, it is the microcomputer, or personal computer (PC), that has come to play the principal role in most office workplaces.
Desktop PCs have become increasingly affordable as a result of industry wide adoption of the architecture of the PC introduced in 1981. Although it has become feasible to provide virtually every office worker with a PC, it is more cost effective for PC users to share files and common peripherals such as printers, facsimile boards, modems, and scanners. In the late 1980s and early 1990s, many companies began programs of linking or networking multiple PCs into a unified system.
The local area network (LAN) was created in response to the need for a standardized system of linking computers together in a company. The most common method used to connect computers to a network is by means of coaxial cables. Newer generation networks use fiber optical connections. When computers are not in close physical proximity, networks may use microwave radio or infrared radiation to link the computers. Microwave radio requires a dish antenna for transmission and reception; infrared radiation requires a lens for transmission and a mirror and lens for reception. Other methods used for wide area networking include telephone and communications satellite linkage.
The need for computer connectivity has established the usefulness of the peripheral device known as the modem. Modems permit two computers to communicate by telephone in order to access databases, transmit files, upload and download facsimile transmissions, and send and receive electronic mail. Early transmission speeds using this equipment were relatively slow—300 baud[2]. Some modems now operate at speeds of more than 50,000 baud and have error checking and data compression features.
Text materials in typed or printed form can be input directly into a computer by means of a scanner. To read text, optical character recognition (OCR) software must first be used to convert printed documents electronically into computer readable files. Scanners obviate the need to rekey printed text in order to input it; they can also be used to input graphic material.
Computer Printers
A considerable volume of office computer output is via the printer. Among the earliest printers used with PCs in business offices were daisy wheel and thimble printers, so called because of the shape of their printing elements[3]. Although their type quality was comparable to that of a typewriter, they were slow and could accommodate only text, not graphic materials. As a result, they have been supplanted in most offices by dot-matrix, ink jet, and laser printers.[4]The dot matrix printer may have a 9 or 24 pin print head. The pins impact the paper through a ribbon, creating patterns of dots in the shape of letters and numbers in multiple fonts and type sizes. The ink jet printer, an advance over the dot matrix, provides both high resolution (the higher the resolution, the better the print quality) and quiet operation. The laser printer represents an even greater advance. Similar in technology to a photocopier[5], it offers speed, high resolution of 300 dots or more per inch, ability to reproduce complex graphics, and silent operation—all of which make it virtually essential for desktop publishing.
Electronic Mail (E-mail)
E-mail has become a key part of the communication networks of most modern offices. Data and messages can be transmitted from one computer to another using telephone lines, microwave links, communications satellites, or other telecommunications equipment. The same message can be sent to a number of different addresses. E-mail is sent through a company's own LAN or beyond, through a nationwide or worldwide communications network. E-mail services use a central computer to store messages and data and to route them to their intended destination. With a subscription to a public E-mail network, an individual PC user needs only a modem and a telephone to send and receive written or vocal messages. Because of the huge amount of E-mail that can be generated, systems have been developed to screen mail[6]for individual users.
Voice Mail
A specialized type of E-mail system, voice mail, is a relatively simple, computer linked technology for recording, storing, retrieving, and forwarding phone messages. It is called voice mail, or voice messaging, because the messages are spoken and left in a voice mailbox. The telephone doubles as a computer terminal, but instead of presenting the information on a computer screen, the system reads it over the phone line, using prerecorded voice vocabulary. The systems are based on special purpose computer chips and software that convert human speech into bits of digital code. These digitized voices are stored on magnetic disks, from which they can be instantaneously retrieved. Callers are offered a menu of choices, and the messages they select are played; they can leave messages in voice mailboxes, or they can access huge computer databases.
Desktop Publishing
Desktop Publishing is the use of a computer and specialized software to combine text and graphics to create a document that can be printed on either a laser printer or a typesetting machine. Desktop publishing is a multiple step process involving various types of software and equipment. The original text and illustrations are generally produced with software such as word processors and drawing and painting programs and with photograph scanning equipment and digitizers. The finished product is then transferred to a page makeup program, which is the software most people think of as the actual desktoppublishing software. This type of program enables the user to lay out text and graphics on the screen and see what the results will be: for refining parts of the document, these programs often include word processing and graphics features in addition to layout capabilities. As a final step, the finished document is printed either on a laser printer or, for the best quality, by typesetting equipment.
Notes
[1] With the increasing incorporation of microchips and microcircuitry into office equipment: incorporation of sth. into sth. else = to incorporate sth. into sth. else, 意为“将……结合进……”。本句可译为：随着微型芯片和微型电路越来越多地进入办公设备，计算机与其他设备之间的界线已不那么分明了。
[2] baud：波特(通信中的符号传输速率单位，每秒传输一个符号称为1波特)。
[3] Among the earliest printers used with PCs in business offices were daisy wheel and thimble printers, so called because of the shape of their printing elements．本句为倒装句，原句应为：Daisy wheel and thimble printers were among the earliest printers used with PCs in business offices... "so called" 为形容词，引出状语，表示伴随情况，对主语进一步说明。
[4] dot-matrix, ink jet, and laser printers：点阵，喷墨，激光打印机。
[5] Similar in technology to a photocopier，...: similar to...: 与……类似或相似；类似于……。此处由形容词短语做状语，表示原因。
[6] to screen mail：筛选或过滤邮件。
Choose the best answer for each of the following:
