1、Unit Eight 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-ROMA compact disc (CD) is a laser-read (also termed “optically read”) data storage device on which audio, video, or textual material can be stored. Althoug
2、h 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 rec
3、ord, 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 cor
4、rection 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.2 During playback, a low-powered laser beam re
5、ads the digital data through the reflective rear surface of the disk.1,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 re
6、cordable 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 6.35 cm (2.5 in) in diameter, but it can be used to record as well as play up to 74 minutes of music. Its small size is made possibl
7、e 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 applicat
8、ion 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 capa
9、city is about 200 megabytes. (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 tex
10、t 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
11、 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
12、 for video will eventually allow movie storage on CD-Is, with a quality comparable to boys laser-recorded videodiscs.,KEY WORDS compact 紧密的 compact disk (简称CD)激光磁盘 optically 光学地，光地 textual 本文的；正文的 stereophonic 立体声的 supplant 代替，取代 potential 潜势(的)，潜力(的) coating 涂层，层 playback 播放(录音带，唱片) uniform 均匀的,psy
13、cho-acoustic 心理(精神)听觉的；传音的 encyclopedia 百科全书 cursor (计算机尺的) 游标，指导(的) tutorial 指导教师(的)，指导(的) variation 变化，变量 at a rate of 以的速率 improve over 在基础上改善 in diameter 直径 in excess of 超过 comparable to 与可比,NOTES1 Although it has been used primarily to record stereophonic sound and has supplanted the long-playi
14、ng 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信息的媒体，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 dat
15、a, tracking codes, and cueing data, are recorded on a digital tape, which is used to make compression-molded plastic disc 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
16、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 ditgital tape”。,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 44,10
17、0 times per second per channel.(4) New data compression techniques can out massive quantities of unneeded data.(5) When the CD is played, nothing mechanical its surface.(6) The CD improves over conventional records with its more and accurate frequency response.,2. True/False.(1) The CD stores more i
18、nformation than the conventional record.( )(2) The CD-ROM is a second important application of CD technology.( )(3) The CD has been used mainly to record stereophonic sound.( )(4) A CD can only store sound.( )(5) The conventional phonograph works in the same manner as a CD.( )(6) A CD-ROM is accesse
19、d through a computer drive.( ),3. Fill in the blanks with the best choice.(1) Compared with other kinds of records, the CD .a. is protected by a clear plastic coatingb. has a less uniform frequency responsec. is read by a powerful laser beamd. consists of 6 binary digits or bits,(2) Which of the fol
20、lowing is true?a. In 1992, the first movie was recorded on a CD-ROM.b. The maximum storage capacity of a hard disk is about 500 megabytes.c. The Academic American Encyclopedia was the first encyclopedia to be made available as a CD-ROM in 1986.d. The usual CD is 6.35 cm in diameter.(3) Which paragra
21、ph tells of the CDs working principles?a. 2 b. 3 c. 4 d. 5,(4) We can infer that .a. the conventional record can also be accessed via a CD-ROM driveb. the conventional record has as long as a service life as the CDc. the CD is much cheaper than the conventional oned. the Photo CD records photos in d
22、igital form(5) The passage is probably taken from .a. a text book b. a computer manualc. an encyclopedia d. a popular magazine,4. Translate the following sentences into Chinese.(1) A compact disc (CD) is a laser-read (also termed “optically read”) data storage device on which audio, video, or textua
23、l 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.(2) The
24、 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 t
25、he surface of the disc when it is played.,Passage B Hard Disks and Optical DisksThe hard disk drive provides increased storage capabilities and faster access. Hard disks were developed by IBM in 1973. The early ones were extremely expensive; however, with mass production of the personal computer, a
26、hard disk drive is now available for as little as $200, and it is incorporated into the computer system. A fixed, hard disk usually has one or more disk platters coated with a metal oxide substance that allows information to be magnetically stored on it. This storage system includes the disk, a read
27、/write head assembly, and the connections between the drive and the computer.,At first, these disk drives used 14 inch disks, but now they use 5 1/4 inch, 3 1/2 inch,2 1/2 inch, and 1 4/5 inch diameters. In contrast to the floppy disk drive, hard disk drives hold from 80 megabytes to gigabytes and t
28、erabytes of information. When purchasing a hard disk, consider storage capacity and seek time, a measure of a hard disks access speed. The smaller the numbers, the faster the disk. In the past, 65 milliseconds was the standard access time, but today the standard is less than 7 milliseconds.,How Is D
29、ata Stored on a Hard Disk?Storing data on hard disks is similar to storing data on diskettes. In order to read or write data on the surface of the spinning disk platter, the disk drives are designed with access arms, or actuators. The access arms, or actuators, contain one or more read/write heads p
30、er disk surface. As the disk rotates at a high rate of speed, usually 3,600 revolution per minute, the read/write heads move across its surface. These read/write heads float on a cushion of air and do not actually touch the surface of the disk. The distance between the head and the surface varies fr
31、om approximately ten to twenty millionths of an inch. If some form of contamination is introduced or if the alignment of the read/write heads is altered by something accidentally jarring the computer, the disk head can collide and damage the disk surface, causing a loss of data. This event is known
32、as a head crash. Because of the time needed to repair the disk and to reconstruct the data that was lost, head crashes can be extremely costly to users in terms of both time and money.,How Is Data Physical Organized on a Hard Disk?Depending on the type of disk drive, data is physically organized in
33、one of two ways. One way is the sector method and the other is the cylinder method.The sector method for physically organizing data on disks divides each track on the disk surface into individual storage areas called sectors. Each sectors can contain a specified number of bytes. Data is referenced b
34、y indicating the surface, track, and sector where the data is stored.,With the cylinder method, all tracks of the same number on each recording surface are considered part of the same cylinder. For example, the fifth track on all surfaces would be considered part of cylinder five. All twentieth trac
35、ks would be part of cylinder twenty and so on. When the computer requests data from a disk using the cylinder method, it must specify the cylinder, recording surface, and record number. Because the access arms containing the read/write heads all move together, they are always over the same track on
36、all surfaces. Thus, using the cylinder method to record data down the disk surfaces reduces the movement of the read/write head during both reading and writing of data.,Advantage of Using a Hard Disk on a Personal ComputerA hard drive on a personal computer provides many advantages for users. Becaus
37、e of its large storage capacity, a hard disk can store many software application programs and data files. When a user wants to run a particular application or access a particular data file on a hard disk, it is always available. The user does not have to find the appropriate diskette and insert it i
38、nto the drive. In addition, the faster access time of a hard disk reduces the time needed to load programs and access data.Enormous quantities of information are stored on optical disks by using a laser to burn microscopic holes on the surface of a hard plastic disk.A lower power laser reads the dis
39、k by reflecting light off the disk surface. The reflected light is converted into a series of bits that the computer can process.,A full-size, 14-inch optical disk can store 6.8 billion bytes of information. The smaller disks, just under five inches in diameter, can store over 800 million characters
40、, or approximately 1,100 times the data that can be stored on a standard density 3 1/2 inch diskette. Thats enough space to store approximately 400,000 pages of typed data. The smaller optical disks are called CD-ROM, an acronym for compact disk read-only memory. They use the same laser technology t
41、hat is used for the CD-ROM disks that have become popular for recorded music.,Most optical disks are prerecorded and cannot be modified by the user. These disks are used for applications such as an auto parts catalog where the information is changed only occasionally, such as once a year, and a new
42、updated optical disk is created.2 Optical disk devices that provide for one-time recording are called WORM devices, an acronym for write once, read many. Erasable optical disk drives are just starting to be used. The most common erasable optical drives use magneto-optical technology, in which a magn
43、etic field changes the polarity of a spot on the disk that has been heated by a laser.Because of their tremendous storage capacities, entire catalogs or reference materials can be stored on a single optical disk. Some people predict that disks will someday replace data now stored on film such as mic
44、rofiche.,KEY WORDS auxiliary storage (also called secondary storage) 辅助存储器 diskettes (also called floppy disk)软盘 hard disks 硬盘 optical disks 光盘 track 磁道 sector 扇区 cylinder 柱面,NOTES1 These read/write heads float on a cushion of air and do not actually touch the surface of the disk. 这些读/写头在高压气流上漂浮，移动时
45、并不与盘片表面真正接触。 cushion也可译为“气垫”。2 These disks are used for applications such as an auto parts catalog where the information is changed only occasionally, such as once a year, and a new updated optical disk is created. 这种光盘用于信息量大，不需要经常更改信息内容的场合。比如，一个汽车零件目录，其中的信息是经过一段时间(如一年)才更改一次，需要更改时再制作一个新的光盘就可以了。 auto
46、 parts catalog可译为“汽车零件目录”。,EXERCISES 1. Fill in the blanks with the best choice.(1) The programs and data that are not currently being processed by the computer are commonly stored on .a. RAM b. EPROM c. auxiliary storage d. ROM(2) Most auxiliary storage devices are .a. volatile b. difficult to read
47、 c. difficult to write d. non-volatile(3) Auxiliary storage devices can be used as devices.a. input b. output c. storage d. all of above,(4) is used as a principal auxiliary storage medium for personal computers.a. CD-ROM b. Diskette c. Tape d. Core memory(5) The time required to retrieve data from
48、a diskette and place it in main memory is called the .a. seek time b. access time c. settling time d. data transfer rate(6) The time used to position the read/write head over the proper track is called .a. seek time b. access time c. rotational delay d. settling time(7) The time it takes for the sec
49、tor containing the data to rotate under the read/ write head is called .a. seek time b. access time c. settling time d. rotational delay,(8) The time required for the read/write head to be placed in contact with the disk is called .a. data transfer rate b. seek time c. settling time d. access time(9) Data is transferred between main memory and the disk surface a at a time.a. track b. sector c. cylinder d. word(10) The formatting process defines on the surfaces of a diskette.a. tracks b. sectors c. cylinders d. all of above,
