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.

因特網能為我們做什么？

因特網有如下四個主要的應用：

    1．電子函件。在因特網上，人們可以創作、發送和接收電子函件。許多人每天收到成打的電子函件信息，這大大超過電話和蝸牛式的普通郵件，他們把它看作與外界交流的主要方式。

    2．新聞。新聞組是供具有共同愛好的用戶交流信息的限定范圍的論壇。在因特網上，有上千個技術性和非技術性的新聞組，涉及計算機、科學、娛樂和政治等專題。

    3.遠程登錄。在因特同任何地方的用戶都可以使用Telnet、Rlogin或其他的程序登錄到他具有帳號的其他計算機上。

    4．文件傳輸。在因特網上，使用FTP程序可以從一臺計算機向另一臺計算機拷貝文件。大量的文章、數據庫及其他信息都可以通過這種方式傳輸。

網絡計算機

    網絡計算機，也叫“因特網烤爐”、因特網裝置、因特網設備，是一種價格低廉、無需維護的臺式裝置。它可以讓用戶不費力氣就能接到因特網和網絡資源上。從這種臺式裝置上，他們就能分享到任何資源，完成所有目前需要在PC機上進行的計算任務。

    網絡計算機提供了簡潔性，去掉了使PC應用復雜化的軟硬件，只留下網絡訪問與顯示功能，實際上，網絡計算機在軟件、服務、處理、數據和資源上全部都依賴網絡。這就消除了周而復始的臺式軟硬件升級，而是把這個負擔放到了網絡上。

    需要最新的字處理軟件或電子表格軟件？將它從服務器上下載來運行即可。需要把你做的工作保存起來嗎？只需把它送上網絡,在那它被安全地存儲并作好備份。

防火墻：一項網絡安全措施

    隨著因特網的普及，網絡的安全性越來越難以保證，網絡遭破壞的事件時有發生。這既有“黑客”們的“光顧”，也有合法授權用戶的“特別關照”。而防火墻就是保證網絡安全的一種有效措施。它可以保證所有的通信符合安全政策。

    曾有兩位年輕人非法侵入了大學網絡，創建了一個公告牌，并在上面裝入了流行的商業軟件，還邀請因特網上的用戶下載這些軟件包。幸好有了防火墻，網絡管理員發現系統遭到了破壞。他們檢查了審計記錄，找到了這兩名學生的IP地址、姓名及地點。警察就逮捕了這兩名“黑客”。

電子函件

    因特網的一個重要應用是計算機用戶間利用電子函件相互通信。電子函件使用戶可以用電子手段傳遞和接收消息、文本和數據。電子函件的功能非常類似于郵箱：無論接收者是否在網絡上，用戶都可以向他發送消息，該消息被保存起來，同時向接收者發送一個信號表明有一個消息在等待處理。

電子函件傳送消息已經代替了電話。用戶可以在方便的時候再去對它作出反應，而不會被打擾，并可以在屏幕上顯示消息或把它打印出來。

電子公告板

　　因特網的另一個有趣的應用是電子公告板，又稱公告服務，簡稱BBS。它允許用戶的投遞或回收消息，這些消息不是針對某一個具體的用戶發送的，它就像在辦公室的公告牌上發布通知一樣。BBS被廣泛應用在從日常服務、招聘廣告到非常專業的領域中，例如在一個非常狹窄的科學領域中交換調查數據。