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ARPANET网的投入运行，为计算机网络发展奠定了基础，其核心技术是分组交换技术。（)
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第6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7题
B.回收前热网加热器疏水第二、三级冷却器冷却水侧投入运行，第三级冷却器生水投入量以热网疏水侧出口温度不超过45℃为准，第三级冷却器热网疏水侧出口至凝汽器阀门开度已疏水箱水位开始下降为准
C.在热网加热器投运初期，第三级冷却器疏水侧出口排放门不允许与出口至凝汽器阀门同时开启
D.汽轮机停机打闸后，在凝汽器无真空前切换疏水箱疏水回化学水处理
第9题
A、错误
B、正确
第11题
