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Unit 5 Auxiliary Storage,Unit 5 Auxiliary Storage,Passage A CD and CD-ROM,Passage B Hard Disks and Optical Disks,Passage C Introduction to CD-ROM,Passage A CD and CD-ROM,A compact disc(CD)is a laser-read(also termed“optically read)data storage device on which audio,video,or textual material can be stored.Although it has been used primarily to record stereophonic sound and has supplanted the long-playing PHONOGRAPH record as the principal medium for music storage,it offers a huge potential as the medium for the storage of massive amounts of many types of information.1,Unlike the conventional phonograph record,the CD stores information in digital form.Stereophonic(two-channel)sound signals are digitally sampled at a rate of 44,100 times per second per channel.Each sample is expressed as a binary number value consisting of 16 binary digits,or bits.The sampled digital values,along with error correction data,tracking codes,and cueing data,are recorded on a digital tape,which is used to make compression-molded plastic discs 12 cm(4.72in)in diameter,each covered by a thin,reflective metallic layer and protected by a clear plastic coating.,2,During playback,a low-powered laser beam reads the digital data through the reflective rear surface of the disk.,The CD improves over conventional records and tape recordings with its more uniform and accurate frequency response,a complete absence of background noise,a wider dynamic range(the difference between the softest and loudest recordable musical sounds),and longer wearsince nothing mechanical touches the surface of the disc when it is played.,Introduced in 1992,the Sony MiniDisc measures only 6.35cm(2.5in)in diameter,but it can be used to record as well as play up to 74 minutes of music.,3,Its small size is made possible by a system of data reduction that uses psycho-acoustic principles to eliminate data that is not normally heard by the listener-thereby reducing the data density to one-fifth that required for conventional CDs.Mini-Discs can be used only with their own recorder-player.,A second important application of CD technology is the CD-ROM (Compact Disc Read Only Memory),a text/graphics/sound storage medium that is accessed through the CD-ROM drive in a computer.A CD-ROM can store in excess of 500 megabytes(millions of bytes)of dataas compared with a computers hard disk,whose maximum storage capacity is about 200 megabytes.,4,(The Academic American Encyclopedia was the first encyclopedia to be made available as a CD-ROM,in 1986).New data compression techniques,which can filter out massive quantities of unneeded data,have expanded CD-ROM capacities to include sound and image as well as text storage:in 1993 the first movie(A Hard Days Night)was recorded on a CD-ROM.,The Interactive Compact Disc,or CD-I,is essentially a CD-ROM that can be accessed via a CD-I player attached to a television set.With an on-screen cursor and a handheld control pad the user can choose his or her own path through a game,an art history tour,or a“How To tutorial that includes CD-quality sound and thousands of full-color images as well as text.Among the variation of the CD-I is the Photo CD,which records still photos digitally,for display on a TV screen.Improved data compression techniques for video will eventually allow movie storage on CD-Is,with a quality comparable to boys laser-recorded videodiscs.,Notes,1 Although it has been used primarily to record stereophonic sound and has supplanted the long-playing PHONOGRAPH record as the principal medium for music,storage,it offers a huge potential as the medium for the storage of massive amounts of many types of information.,尽管CD最初用于记录立体声声音并且已经取代了留声机唱片而成为主要的音乐存储媒体,但它作为能存储大量多种信息的媒体仍具有巨大的潜力。,2 The sampled digital values,along with error correction data,tracking codes,and cueing data,are recorded on a digital tape,which is used to make compression-molded plastic discs 12 cm(4.72 in)in diameter,each covered by a thin,reflective metallic layer and protected by a clear plastic coating.,采样的数据连同纠错数据、道代码和提示数据被记录在数字带上,数字带常常做成直径为12 cm(4.72英寸)的模压型塑料片,每片都覆盖一层薄薄的反光金属,其外层有一层透明塑料保护层。,along 意为“连同。,error correction data 意为“纠错数据。,“which is 为定语从句,修饰“a digital tape。,3 Introduced in 1992,the Sony MiniDisc measures only 6.35 cm(2.5 in)in diameter,but it can be used to record as well as play up to 74 minutes of music.,1992年引进的索尼迷你盘直径只有6.35 cm(2.5 英寸),但它可以录制以及播放长达74分钟的音乐。,as well as 意为“以及,“和。,play up to意为“播放长达。,4 A CD-ROM can store in excess of 500 megabytes(millions of bytes)of data-as compared with a computers hard disk,whose maximum storage capacity is about 200 megabytes.,和计算机硬盘相比,一个只读存储器可以存储超过500 MB的数据,它的最大存储容量大约为200 MB。,in excess of意为“超过。,compare with意为“和相比。,whose引导定语从句,修饰CD-COM。,注：本文选自较早文献，目前计算机硬盘技术得到了快速开展，其容量已突破100 GB。,Exercises,1.Fill in the blanks.,(1)A,disc(CD)is a laser-read data storage device.,(2)The CD stores information in,form.,(3)Stereophonic sound signals are digitally,at a rate of 44,100 times per second per channel.,(4)New data compression techni
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