Internet  has  four  main  applications  as  follows：

    l．E－mail． With Internet， people can compose， send， and receive electronic mails． Many people get dozens of messages a day and consider it as their primary way of interacting with the outside world, far outdistancing the telephone and snail mail.

    2．News． Newsgroups are specialzied forums in which users with a common interest can  exchagne messages．Thousands of newsgroups exist on Internet，on technical and nontechnical topics，including computers，science，recreation，and politics．

    3．Remote login．Using the Telnet，Rlogin, or other programs， the  user anywhere on  Internet can log into any other machine  on  which  he  has  an  account．

    4． File transfer．Using the FTP program， it is possible to copy files from one machine on Internet to another． Vast numbers of articles， databases， and  other information are available in this way．

The Network Computer

    The network computer， also known as the Internet toaster，Internet appliance or Internet device，is the low cost，no　maintenance desktop device． It allows users to effortlessly connect to　Internet and network resources． From there， they can share any　resource and perform all computing tasks that they currently do on　their PCs．

    The network computer offers simplicity．Stripped of the　hardware and software that　complicate the PC life and only capable of network access and display, the network computer relies on the network for virtually all software， services， processing， data， and resources． It eliminates the continuous cycle of desktop hardware and software upgrades， pushing that burden instead on to the network．

    Need the latest word processor or spreadsheet？ Run it off the server， Want to save your work？ Just send it off to the network，where it will be stored secured, and backed up．

Firewall： a Measure of Network Security

    With the popularity of Internet，it is increasingly difficult to guarantee the network security．Sometimes the network  was breached because of not only hackers’ visit but also authorized users’ care out of ordinary. Firewall just is an effective measure of network security．It will ensure that all communications conform to your Security policy．

    Once two lads broke into the university network，created a bulletin board，loaded popular commercial software on it and invited users across Internet to download the packages．Thanks to a firewall, network administrators found the system breached. They checked the audit and found the students’ IP addresses， names and location． The police arrested the two hackers．

E－mail

    One important application for Internet is communication between computer users by the electronic mail，or E－mail． E－mail allows users to electronically transmit and receive messages，text， or data．E-mail functions futher like a mailbox：the user can send messages whether or not the intended receiver is currently on the network and the message is stored， along with a signal for the receiver that indicates that there is a message waiting．

   E-mail has replaced the telephone for many messages．Users can respond when it is convenient，without being interrupted,  and can get their message either on-screen or in the printed form．

  Electronic Bulletin Boards

Another interesting application for Internet is the electronic bulletin board which is also called bulletin board service, BBS for short. It allows users to post and retrieve messages that are not directed to a specific user, much like announcements are posted on an office bulletin board. BBS has been used for everything from dating service and want ads to highly specialized applications such as the exchange of research data in a narrow scientific field.

因特网能为我们做什么？

因特网有如下四个主要的应用：

    1．电子函件。在因特网上，人们可以创作、发送和接收电子函件。许多人每天收到成打的电子函件信息，这大大超过电话和蜗牛式的普通邮件，他们把它看作与外界交流的主要方式。

    2．新闻。新闻组是供具有共同爱好的用户交流信息的限定范围的论坛。在因特网上，有上千个技术性和非技术性的新闻组，涉及计算机、科学、娱乐和政治等专题。

    3.远程登录。在因特同任何地方的用户都可以使用Telnet、Rlogin或其他的程序登录到他具有帐号的其他计算机上。

    4．文件传输。在因特网上，使用FTP程序可以从一台计算机向另一台计算机拷贝文件。大量的文章、数据库及其他信息都可以通过这种方式传输。

网络计算机

    网络计算机，也叫“因特网烤炉”、因特网装置、因特网设备，是一种价格低廉、无需维护的台式装置。它可以让用户不费力气就能接到因特网和网络资源上。从这种台式装置上，他们就能分享到任何资源，完成所有目前需要在PC机上进行的计算任务。

    网络计算机提供了简洁性，去掉了使PC应用复杂化的软硬件，只留下网络访问与显示功能，实际上，网络计算机在软件、服务、处理、数据和资源上全部都依赖网络。这就消除了周而复始的台式软硬件升级，而是把这个负担放到了网络上。

    需要最新的字处理软件或电子表格软件？将它从服务器上下载来运行即可。需要把你做的工作保存起来吗？只需把它送上网络,在那它被安全地存储并作好备份。

防火墙：一项网络安全措施

    随着因特网的普及，网络的安全性越来越难以保证，网络遭破坏的事件时有发生。这既有“黑客”们的“光顾”，也有合法授权用户的“特别关照”。而防火墙就是保证网络安全的一种有效措施。它可以保证所有的通信符合安全政策。

    曾有两位年轻人非法侵入了大学网络，创建了一个公告牌，并在上面装入了流行的商业软件，还邀请因特网上的用户下载这些软件包。幸好有了防火墙，网络管理员发现系统遭到了破坏。他们检查了审计记录，找到了这两名学生的IP地址、姓名及地点。警察就逮捕了这两名“黑客”。

电子函件

    因特网的一个重要应用是计算机用户间利用电子函件相互通信。电子函件使用户可以用电子手段传递和接收消息、文本和数据。电子函件的功能非常类似于邮箱：无论接收者是否在网络上，用户都可以向他发送消息，该消息被保存起来，同时向接收者发送一个信号表明有一个消息在等待处理。

电子函件传送消息已经代替了电话。用户可以在方便的时候再去对它作出反应，而不会被打扰，并可以在屏幕上显示消息或把它打印出来。

电子公告板

　　因特网的另一个有趣的应用是电子公告板，又称公告服务，简称BBS。它允许用户的投递或回收消息，这些消息不是针对某一个具体的用户发送的，它就像在办公室的公告牌上发布通知一样。BBS被广泛应用在从日常服务、招聘广告到非常专业的领域中，例如在一个非常狭窄的科学领域中交换调查数据。