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.

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．

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．

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， 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．

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．

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．

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.

Literally, multimedia means TWO or more media．If the publisher of this book Wanted to join the Current hype about　multimedia，he could advertise the book as using multimedia　technology．After all，it contains two media：text and graphics(the figures). Nevertheless，when most pepole refer to multimedia，they generally mean the combination of two or more continuous media，that is， media have to be played during some well-defined timed times interval, usually With the users interaction．In practice，the two media are normally audio and video，that is，sound plus moving pictures．

In the multimedia environment，

we have graphics and text at the same time，we can also add the photograph, animation，good-quality sound, and full motion video．All of the technologies make computers more interesting and much easier to use．For example, a multimedia program can play a segment of movie：a cat was playing a reel of thread, with "mewing…" The tableau can a be immediately captured and pasted to a text at the side of a paragraph of words．

Musical Instrument Digital Interface，or MIDI，is a communication interface provided on virtually every synthesizer made today. It provides a standard that allows Products by different companies to communicate with each other. MIDI’s original purpose as to allow a musician to control several synthesizers from one keyboard rather than connecting a number of keyboard-equipped synthesizers，to produce the multilayered sound．The MIDI standard provides for 16 channels．You can assign each channel to a specific synthesizer or synthesizer voice. If you record a sequence and assign it to channel 5, for example, only an instrument set to listen on channel 5 plays back the sequence, this feature enables MIDI networks to sound like orchestras．