1 / 35

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

kleland
Download Presentation

Unit 5 Auxiliary Storage

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Unit 5 Auxiliary Storage Passage A CD and CD-ROM Passage B Hard Disks and Optical Disks Passage C Introduction to CD-ROM

  2. 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]

  3. 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 (4.72 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 reads the digital data through the reflective rear surface of the disk.

  4. 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 wear—since 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. [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.

  5. 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 data—as compared with a computer’s 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 Day’s Night) was recorded on a CD-ROM .

  6. 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 boy’s laser-recorded videodiscs.

  7. 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。 

  8. 　　［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”。 

  9. 　　［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……”。 

  10. 　　［4］ A CD-ROM can store in excess of 500 megabytes (millions of bytes) of data-as compared with a computer’s 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发展， 其容量已突破100 GB。

  11. 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 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.

  12. 2.  True/False. (1)  The CD stores more information 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 accessed through a computer drive.( )

  13. 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 coating b. has a less uniform frequency response c. is read by a powerful laser beam d. consists of 6 binary digits or bits

  14. (2)  Which of the following 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 paragraph tells of the CD’s working principles? a. 2 b. 3 c. 4 d. 5

  15. (4)  We can infer that . a. the conventional record can also be accessed via a CD-ROM drive b. the conventional record has as long as a service life as the CD c. the CD is much cheaper than the conventional one d. the Photo CD records photos in digital form

  16. 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 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. (2)  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 wear—since nothing mechanical touches the surface of the disc when it is played.

  17. Passage B Hard Disks and Optical Disks The 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 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/write head assembly, and the connections between the drive and the computer.

  18. 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 terabytes of information. When purchasing a hard disk, consider storage capacity and seek time, a measure of a hard disk’s 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.

  19. How Is Data 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.[1] The access arms, or actuators, contain one or more read/write heads per 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.[2] The distance between the head and the surface varies from 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 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.

  20. How Is Data Physical Organized on a Hard Disk? Depending on the type of disk drive, data is physically organized in 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 by indicating the surface, track, and sector where the data is stored.

  21. 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 tracks 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 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.

  22. Advantage of Using a Hard Disk on a Personal Computer A hard drive on a personal computer provides many advantages for users. Because 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 into 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.

  23. A lower power laser reads the disk 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, or approximately 1,100 times the data that can be stored on a standard density 3 1/2 inch diskette. That’s 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 that is used for the CD-ROM disks that have become popular for recorded music.

  24. 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 updated optical disk is created.[3] 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 magnetic field changes the polarity of a spot on the disk that has been heated by a laser.[4]

  25. 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 microfiche.

  26. Notes 　　［1］ 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. 　　在硬盘上存储数据类似于在软盘上存储数据。 为了在旋转的磁盘盘片表面读取或写入数据, 磁盘驱动器被设计成具有存取和传动装置。  · be similar to意为“与……相同”。  · in order to意为“为了……”。 

  27. 　　［2］ 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, 移动时并不与盘片表面真正接触。  · cushion可译为“气垫”。  　　［3］ 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 parts catalog可译为“汽车零件目录”。 

  28. 　　［4］ The most common erasable optical drives use magneto-optical technology, in which a magnetic field changes the polarity of a spot on the disk that has been heated by a laser. 　　最常见的可擦写光盘驱动使用磁光技术, 在这种技术中磁场改变了磁盘上被激光加热的点的极性。  · in which引导状语从句, 修饰technology。 

  29. Exercises 1. Please translate the following phrases into English. (1) 硬盘驱动 (2) 辅助存储器 (3) 存储容量 　 　 (4) 读/写磁头 (5) 只读存储器 　　(6) 硬盘 (7) 光盘 　　　 (8) 软盘 

  30. 2. Please translate the following sentences into Chinese. (1) In contrast to the floppy disk drive, hard disk drives hold from 80 megabytes to gigabytes and terabytes of information. When purchasing a hard disk, consider storage capacity and seek time, a measure of a hard disk’s access speed. The smaller the numbers, the faster the disk. (2) 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.

  31. (3) The sector method for physically organizing data on disks divides each track on the disk surface into individual storage areas called sectors. Each sector can contain a specified number of bytes.  (4) 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 microfiche.

  32. Passage C Introduction to CD-ROM Since compact discs store audio in a digital format they are suitable for storing other digital information. In 1984, Phillips and Sony released the Compact Disc Read Only Memory (CD-ROM) specification, known as the Yellow Book. This defines the necessary additions to the Red Book for the storage of computer data. The physical parameters of CD-ROMs are identical to those defined in the Red Book. The use of the data it contains is different. While audio CDs can be played at only one speed, CD-ROM drives exist with a range of speed options from normal (1x) to four times normal speed (4x) and, now, 52x. As the speed increases the access time also decreases.

  33. CD-ROM discs differ from CD audio discs in two important ways. The data on a CD-ROM disc are divided into sectors which contain both user data and other data for control and (additional) error protection. The data on a CD-ROM are contained in files. All CD-ROMs therefore need a file system to enable the computer to access the required file easily and quickly. The user normally will not need to be bothered with the sector structure but will be aware of the file structure of the files on a CD-ROM.

  34. In order to use CD-ROMs you need to buy a CD-ROM drive (sometimes called a CD reader) and connect it to your computer. A CD-ROM has several advantages over other forms of data storage, and a few disadvantages. It can hold 650 megabytes (MB) of data, the equivalent of nearly 500 high density floppy disks. The data on a CD-ROM can be accessed much more quickly than data on a tape, but CD-ROMs are considerably slower than hard discs. Like audio CDs you cannot write to a CD-ROM (but CD recordable discs do exist), so they are only used for pre-recorded data. In addition CD-E (Compact Disc Erasable) is now being introduced, which will enable you to re-record data on the CD.

  35. As CD-ROM speeds continue to increase, we are finding that traditional reading technologies are approaching apparent limits. CAV (constant angular velocity) reading technology dominates today’s CD-ROM drives, yet the very nature of the technology imposes a performance ceiling. CAV readers work by maintaining a constant RPM (revolutions per minute) no matter what portion of the disc is being read. This means that in order to increase a drive’s x rating, the RPM must be increased. Mechanical limitations in current technology have maxed out today’s CAV readers at 56x. This equates to spin rates in the neighborhood of 12,000 RPM! Compare this to hard disk drive technology and we find that only Seagate’s 15,000 RPM drive spins at a faster rate. Yet the engineering involved in making a sturdy, reliable hard drive far outshines what goes into a $70 CD-ROM drive. How much faster can CAV CD-ROM drives get and still maintain their dirt-cheap pricing?

More Related