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 600megabyte capacity and are well suited for the computer applications needing the vast storage．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存数据。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。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．
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。
Musical Instrument Digital Interface
音乐设备数字接口
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．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。The MIDI standard provides for 16channels．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 5plays back the sequence，this feature enables MIDI networks to sound like orchestras．
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。
Audio
声波
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.
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。
Virtual Reality—Enter a Fancy Space
虚拟现实——进入想象的空间
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．
威廉·吉布森在他的科幻小说《神经漫游者》中描述了一个由计算机控制的空间——电脑空间，一个人只要将自己的大脑与计算机连接起来，进入电脑空间，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。这个电脑空间被认为是未来虚拟现实的目标。
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...
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。
