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.

　　CD－ROM

　　CD－ROM is an optical technology that is used to make compact disks for CD stereo systems；it has now been adapted to store data for computers. CD disk is an optical disc, on which data is recorded as a set of dips in the surface. When a laser beam shines across the dips, the reflected distortion represents the data. Optical disc has a 600 megabyte capacity and are well suited for the computer applications needing the vast storage. The playback effect of optical discs for music is very perfect, no hiss and crackle as with other photo-records. A computer system must have a CD drive that is designed to read the disks and translate the data into a form it can process. CD disks can store huge volumes of data and are very useful for reference material an encyclopedia, for example. However, as the name(read-only memory)implies, CD disks cannot be written on or changed in any way.

　　Musical Instrument Digital Interface

　　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.

　　Audio

　　An audio(sound) wave is a one-dimensional acoustic(pressure) wave. When an acoustic wave enters the ear, the eardrum vibrates, causing the tiny bones of the inner ear to vibrate along with it, and sending nerve pulses to the brain. These pluses are perceived as sound by the listener. Audio waves can be converted to digital form by an ADC (Analog Digital Converter). An ADC takes an electrical voltage as input and generates a binary number as output. Music, of course, is just a special case of general audio, but an important one. The representation, processing, storage, and transmission of such audio signals are a major part of the study of multimedia systems.

　　Virtual Reality－Enter a Fancy Space

　　In the science fiction "Neuromancer", William Gibson describes a space, Cyberspace, controlled by a computer. Once his brain was linked with the computer, a man would undergo all experiences in the space. His various senses in the realistic world would be replaced with a series of new electric stimuli. The Cyberspace is regarded as a goal of future virtual reality.

　　In fact, virtual reality is exploiting software and hardware of the computer to generate a simulation of an environment, such as an easeful classroom, a breathtaking action and so on. In such a simulated environment, one would have an immersed sense. For example, in a Virtual space, Students can "dissect" a human body, "visit" ancient battlefields, or "talk" with Shakespeare, …

　　“多媒体”到底意味着什么？

　　从字面上看，多媒体是指两种或两种以上媒体。如果本书的出版者想加入当前多媒体广告的行列，那么，他就可以声称这本书已经使用了多媒体技术。因为，毕竟，它包含两种媒体，文本和图形（插图）。然而，当大多数人谈及多媒体时，他们通常是指混合了两种或两种以上连续的媒体，即，媒体可以在一段规定的时间之内连续播放，并且通常伴随着与用户的交互。实际上，这两种媒体通常指音频和视频，即声音加移动的图片。

　　在多媒体环境中，我们可以同时拥有图形和文本，也可以增加图片、动画、高质量的音响和全动录像，这些技术使得计算机使用起来更有趣也更容易。例如，一个多媒体程序可以播放一段电影：一只小猫正在玩线团，发出“喵喵”的声音……，这个画面可以立即剪贴到一段文字旁边。

　　CD-ROM

　　CD－ROM原是一种用于制作CD立体声系统的小型圆盘的光学技术，现在它已经被用来为计算机储藏数据。CD盘是一种光盘，其数据以一组坑的形式记录在光盘表面上，当激光束扫过这些坑的时候，返回的失真程度就代表了这些数据。光盘有600兆字节的容量，非常适合需要大存储量的计算机应用。音乐光盘播放音乐的效果非常完美，没有像用其他唱片那样的嘶嘶声和噼啪声。计算机系统必须配备一个CD驱动器用来读取光盘并将数据转换到计算机能够处理的形式。CD盘可以储存大量数据，这对于文献资料的存储非常有用，如存储一部百科全书。然而，正如其名字（只读存储器）所指出的那样，CD盘不能写，也不能用任何方式改变其内容。

　　音乐设备数字接口

　　音乐设备数字接口，或称MIDI，实际上是为目前制造的各种合成器提供的一种通信接口。它提供的标准允许不同厂家生产的音乐产品可以进行通信。MIDI原本的目的并不是为了连接许多装备了键盘的合成器来产生多层次的声音,而是为了使音乐家能够用一个键盘控制几个合成器进行演奏。MIDI标准提供16个声道，你可以为每一个声道设置一个特别的合成器或合成器声音。例如，你记录了一个音乐序列并将它设置到第五声道上，并且只有一种乐器在第五声道上回放这个音序，其效果使MIDI网听起来很像乐队。

　　声波

　　声波是一维的声学（气压）波，当声波进入人的耳朵时，耳膜振动，引起耳朵内部的一些小骨头振动，并向大脑发出神经脉冲，这些脉冲被听者作为声音听到了。声波可以通过ADC（模拟数字转换器）转换到数字形式，ADC采用电压作为输入并产生二进制数作为输出。当然，音乐是声波的一种特殊情况，但却是重要的一种。这些音频信号的表达、处理、存储和转换是多媒体系统研究的主要部分。

　　虚拟现实——进入想像的空间

　　William Gibson在他的科幻小说《Neuromancer》中描述了一个计算机控制空间Cyberspace，一个人只要将自己的大脑与计算机连接起来，进入Cyberspace，就可以体验在该空间的一切遭遇。一套全新的电子刺激将代替人在真实世界的各种感觉。这个Cyberspace被认为是未来虚拟现实的目标。

　　实际上，虚拟现实就是利用计算机的软件和硬件去产生一种境界的仿真，如仿真一个学习场所，一次惊险的行为等等，人在这个仿真的环境中，有一种“身临其境”的感觉。如，在虚拟的空间中，学生们可以“解剖”人体，“参观”古战场，与莎士比亚“对话”等等。