第八章计算机专业英语2008年影印版word.doc

P213SECONDARY STORAGEIntroductionSecondary storage devices are used to save, to back up, and even to transport files consisting of data or programs from one location or computer to another. Not long ago, almost all files contained only numbers and letters. The demands for saving these files were easily met with low-capacity floppy disk drives and hard-disk drives.Data storage has expanded from text and numeric files to include digital music files, photographic files, video files, and much more. These new types of files require secondary storage devices that have much greater capacity.Secondary storage devices have always been an indispensable element in any computer system. They have similarities to output and input devices. Like output devices, secondary storage devices receive information from the system unit in the form of the machine language ofOs and Is. Rather than translating the information, however, secondary storage devices save the information in machine language for later use. Like input devices, secondary storage devices send information to the system unit for processing. However, the information, since it is already in machine form, does not need to be translated. It is sent directly to memory (RAM), where it can be accessed and processed by the CPU.Competent end users need to be aware of the different types of secondary storage. They need to know the capabilities, limitations, and uses of floppy disks, hard disks, optical discs, and other types of secondary storage. Additionally, they need to be aware of specialty storage devices for portable computers and to be knowledgeable about how large organizations manage their extensive data resources.辅助存储设备被用来保存，备份，甚至把数据或程序从一个位置或计算机传送到另一个地方。前不久，几乎所有的文件只包含数字和字母。保存这些文件的要求很容易满足，只需要低容量的软盘驱动器和硬盘驱动器。 来自于文字和数字文件不断扩大的数据存储，包括数字音乐文件，照相文件，视频文件，以及更多其他。这些新类型的文件需要有更大容量的辅助存储设备。不断扩大，从文字和数字文件的数据存储，包括数字音乐文件，照相文件，视频文件，以及更。这些新类型的文件需要有更大容量的二级存储设备。 辅助存储设备一直师在任何计算机系统中不可缺少的元素。他们和输出和输入设备有相似之处。像输出设备一样，辅助存储设备从系统单元接收的信息是0和1的机器语言的形式。然而，辅助存储设备上用机器语言保存信息是为了供以后使用，而不是转换信息。像输入设备一样，辅助存储设备将信息发送到系统的单元进行处理。然而，这些信息，因为它们已经是机器的形式，并不需要转换。它们直接发送到存储器（RAM），在那里它们可以被CPU直接访问和处理。有能力的最终用户需要认识到不同类型的辅助存储器。他们需要知道的软盘，硬盘，光盘，和其他类型的辅助存储器的能力，限制，并使用。此外，他们还需要了解便携式计算机的专业存储设备和大型组织如何管理其广泛的数据资源的知识。P214STORAGEAn essential feature of every computer is the ability to save, or store, information. As discussed in Chapter 6, random-access memory (RAM) holds or stores data and programs that the CPU is presently processing. Before data can be processed or a program can be run, it must be in RAM. For this reason, RAM is sometimes referred to as primary storage.Unfortunately, most RAM provides only temporary or volatile storage. That is, it loses all of its contents as soon as the computer is turned off. Its contents also are lost if there is a power failure that disrupts the electric current going into the system unit. This volatility results in a need for more permanent or nonvolatile storage for data and programs. We also need external storage because users need external more storage capacity than is typically available in a computers primary of RAM memory.每一台计算机的一个重要功能是保存或储存信息的能力。像在第6章讨论的，随机存取存储器（RAM）持有或存储CPU现在处理的数据和程序。在数据可以被处理或程序可以运行之前，它们必须在RAM中。出于这个原因，RAM有时也被称为主存储器。不幸的是，大多数RAM仅提供临时或非易失性存储。也就是说，一旦关闭计算机后它就失去它的所有内容。如果有电源故障中断系统单元的供电，其内容也丢失。这种波动的结果需要更多的永久或非易失性存储数据和程序。我们还需要外部存储-因为用户需要比通常计算机需要的RAM内存更多的外部存储容量。Secondary storage provides permanent or nonvolatile storage. Using secondary storage devices such as a floppy disk drive, data and programs can be retained after the computer has been shut off. This is accomplished by writing files to and reading files from secondary storage devices. Writing is the process of saving information to the secondary storage device. Reading is the process of accessing information from secondary storage. This chapter focuses on secondary storage devices.Some important characteristics of secondary storage includeMedia are the actual physical material that holds the data and programs. (See Figure 8-1.) Capacity measures how much a particular storage medium can hold.Storage devices are hardware that reads data and programs from storage media. Most also write to storage media.Access speed measures the amount of time required by the storage device to retrieve data and programs.Most desktop microcomputer systems have floppy, hard, and optical disk drives.辅助存储提供永久或非易失性存储。使用辅助存储设备如软盘驱动器，数据和程序可以在电脑关闭后被保存。这是通过从辅助存储设备写入文件和读取文件。写入是信息存储在辅助存储设备的过程 。读是从辅助存储访问信息的过程。本章重点在辅助存储设备上。二级存储的一些重要特征包括媒体是保存数据和程序的实际物理材料。（见图8-1）。一个特定的存储介质可以容纳的容量程度。存储设备是在存储介质上读取数据和程序的硬件。很多时候也写入到存储介质。访问速度程度是存储设备来检索数据和程序所需的时间。大多数台式微机系统都有软盘，硬盘，和光盘驱动。FLOPPYDISKSFloppy disks are portable or removable storage media. They are typically I used to store and transport relatively small word processing, spreadsheet, and other types of files. They use flexible flat circular pieces of Mylar plastic that have been coated with a magnetic material. Floppy disk drives (FDD) store data and programs by altering the electromagnetic charges on the disks surface to represent Is and Os. Floppy disk drives retrieve data and programs by reading these charges from the magnetic disk. Characters are represented by positive (+) and negative (-) charges using the ASCII, EBCDIC, or Unicode binary codes. For example, the number 3 would require a series of 8 charges. (See Figure 8-2.)软盘是便携式或移动存储介质。它们通常是我用来储存和运输相对较小的文字处理，电子表格，和其他类型的文件。他们使用柔性扁圆形块塑料里面涂上了一层磁性材料。软盘驱动器（FDD）通过改变磁盘的表面上的静电所代表1和0来存储数据。软盘驱动器通过读取磁盘上的这些电荷来检索数据和程序。在ASCII，EBCDIC或Unicode二进制代码中字符由正（+）和负（ - ）电荷表示。例如，数字3将需要8个电荷表示。P215TRADITIONAL FLOPPY DISKThe traditional floppy disk is the 1.44 MB 2HD 3/2-inch disk; 2HD means two-sided, high-density. Two-sided indicates that data can be stored on both sides of the disk. Density refers to how tightly the bits (electromagnetic charges) can be packed next to one another. These disks have a capacity of 1.44 megabytesthe equivalent of over 350 typewritten pages.Floppy disks have a thin exterior jacket made of hard plastic to protect the flexible disk inside. (See Figure 8-3.) A shutter on the disk slides to the side to expose the recording surface. Labels provide users with an area to write or document the contents of the disk. The write- protection notch has a slide that opens and closes. In either position, files can be read from the floppy disk. When the notch is closed, files can be saved to the disk. In the open position, files cannot be saved to the floppy disk.传统的软盘传统的软盘是1.44 MB2HD3.5英寸磁盘;2HD意味着两个片面的，高密度。双面显示，可以在磁盘双方上存储的数据。密度指的是多么紧密位（电磁收费）可以装到另一个。这些磁盘容量为1.44兆字节，相当于超过350打字机页。软盘有薄的外部硬塑料制成的护套保护灵活的磁盘内。 （见图8-3）。快门磁盘上的幻灯片，一边记录面暴露。标签提供了一个地区的用户编写或文件的磁盘上的内容。写保护缺口已经打开和关闭的幻灯片。在任一位置，可将文件从软盘读取。当缺口是封闭的，可将文件保存到磁盘。在打开的位置，文件不能被保存到软盘上。As we discussed in Chapter 5, files are stored and organized on the flexible disk according to tracks and sectors. Tracks are rings of concentric circles without visible grooves. Each track is divided into invisible wedge-shaped sections called sectors. Each tracks sector can store up to 512 bytes or characters.To see how a floppy disk drive works, visit our Web site at www. and enter the keyword disk.正如我们在第5章讨论，文件存储和组织上的灵活的磁盘磁道和扇区。曲目的同心圆环，无可见的凹槽。每个磁道分为无形的楔形部分，称为部门。每个轨道最多可存储512个字节或字符。要看看如何软盘驱动器的工作原理，请访问我们的网站WWW。 和输入的关键字磁盘。HIGH-CAPACITY FLOPPY DISKSHigh-capacity disks are also known as floppy disk cartridges. Like the traditional floppy, the high-capacity disks are 3.5 inches in diameter. However, they are able to store more information, are thicker, and require special disk drives. The most widely used high-capacity disk is the Zip disk produced by Iomega. These disks typically have a 100 MB, 250 MB, or 750 MB capacityover 500 times as much as todays standard floppy disk. Zip disks are typically used to store multimedia, database, large text, and spreadsheet files. (See Figure 8-4.)高容量软盘高容量磁盘也被称为软盘墨盒。传统的软盘一样，高容量磁盘的直径为3.5英寸。但是，它们能够存储更多的信息，更厚，需要特殊的磁盘驱动器。最广泛使用的高容量磁盘是由Iomega Zip磁盘。这些磁盘通常有一个100 MB，250 MB或750 MB的能力超过500倍，今天的标准软盘。 Zip磁盘通常用来存储多媒体，数据库，大型文本和电子表格文件。 （见图8-4）。Figure 8-4 Zip disk and driveP216At one time, floppy disks were adequate to handle most storage requirements and floppy disk drives were a standard feature of most system units. Floppy disks, however, do not have the capacity to store most of todays video and music files. As a result, floppy disks and floppy disk drives are not as widely used.在同一时间，软盘足以应付大多数的存储需求和软盘驱动器是大多数系统单位的标准功能。然而，软盘，没有容量来存储大部分今天的视频和音乐文件。因此，软盘和软盘驱动器不被广泛使用。P EEMSQQSQDiscuss four important characteristics of secondary storage.What is the traditional floppy disk? What is a high-capacity floppy disk?What is density? What are tracks and shutters?HARD DISKSLike floppy disks, hard disks save files by altering the magnetic charges of the disks surface. While a floppy disk uses a thin flexible plastic disk, a hard disk uses thicker, rigid metallic platters that are stacked one on top of another. Hard disks store and organize files using tracks, sectors, and cylinders. A cylinder runs through each track of a stack of platters. Although not needed by floppy disks that have a single platter, cylinders are necessary to differentiate files stored on the same track and sector of different platters. When a hard disk is formatted, tracks, sectors, and cylinders are assigned.Compared to floppy disks, hard disks are able to store and retrieve information much faster and have a greater capacity. They are, however, sensitive instruments. Their read/write heads ride on a cushion of air about 0.000001 inch thick. It is so thin that a smoke particle, fingerprint, dust, or human hair could cause what is known as a head crash. (See Figure 8-5.)A head crash occurs when a read/write head BK makes contact with the hard disks surface or with particles on its surface. A head crash is a disaster for a hard disk. The disk surface is scratched and some or all of the data is destroyed. At one time, head crashes were commonplace. Now, fortunately, they are rare.There are three types of hard disks: internal hard disk, hard-disk cartridge, and hard-disk pack.硬盘像软盘，硬盘文件保存改变磁盘表面的磁荷。虽然软盘使用薄的弹性塑料盘，硬盘使用较厚，刚性，叠在另一个上面一个金属盘片。硬盘存储和组织文件使用的轨道，部门和气瓶。一个圆柱体通过每一个盘片栈的轨道运行。虽然不是需要有一个单碟的软盘，柱面要区分在同一磁道上和扇区不同的盘片上存储的文件。当硬盘被格式化，磁道，扇区，和柱面被重新分配。与软盘相比，硬盘能够存储和检索信息的速度更快，更大的容量。然而，他们是敏感的仪器。他们的读/写磁头乘势而上约0.000001英寸厚的空气垫。它是如此之薄，烟雾粒子，指纹，灰尘，或人的头发可能会导致什么是头崩溃。 （见图8-5）。头部发生崩溃时，一个读/写头BK使得硬盘的表面，或在其表面的颗粒接触。头部碰撞是硬盘的灾难。磁盘表面划伤和部分或全部数据被破坏。一次，头崩溃是家常便饭。现在，幸运的是，他们是罕见的。有三种类型的硬盘：内置硬盘，硬盘硬盘盒，硬盘包。INTERNAL HARD DISKAn internal hard disk is located inside the system unit. For most microcomputer systems, the internal hard disk drive is designated as the C drive. It is used to store programs and large data files. For example, nearly every microcomputer uses its internal hard disk to store its operating system and major applications such as Word and Excel.Internal hard disks have two advantages over floppy disks: capacity and access speed. A 700-gigabyte internal hard disk, for instance, can hold almost as much information as 490,000 standard floppy disks. Because hard disks rotate faster and their read/write heads are closer to the recording surface, the time required to find and retrieve information (access speed) is much faster than for floppy disks. For these reasons, almost all of todays powerful applicationsP217are designed to be stored on and run from an internal hard disk. To see how a hard disk works, visit our Web site at and enter the keyword disk.To ensure adequate performance of your internal hard disk, you should perform routine maintenance and periodically make backup copies of all important files. For hard-disk maintenance and backup procedures, refer to Chapter 5s coverage of the Windows utilities Backup, Disk Cleanup, and Disk Defragmenter.HARD-DISK CARTRIDGES While internal hard disks provide fast access, they have a fixed amount of storage and cannot be easily removed from the system cabinet. Hard-disk cartridges are as easy to remove as a cassette from a videocassette recorder. The amount of storage available to a computer system is limited only by the number of cartridges.Hard-disk cartridges are used primarily to complement an internal hard disk. Because the cartridges are easily removed, they are particularly useful to protect or secure sensitive information. Other uses for hard-disk cartridges include backing up the contents of the internal hard disk and providing additional hard-disk capacity.Hard-disk cartridges for desktop computers have typical capacities of 20 to 100 GB (gigabytes). One of the most widely used hard-disk cartridges is the Removable Hard Disk from Iomega. (See Figure 8-6.) Credit card-size hard-disk cartridges called PC Card hard disks are available for notebook computers with typical capacities up to 5 gigabytes. Two well-known PC Card hard disks are IBMs Microdrive and Toshibas MK5002. (See Figure 8-7.)P218HARD-DISK PACKSHard-disk packs are removable storage devices used to store massive amounts of information. (See Figure 8-8.) Their capacity far exceeds the other types of hard disks. Although you may never have seen one, it is almost certain that you have used them. Microcomputers that have access to the Internet, minicomputers, or mainframes often have access to external hard-disk packs through communication lines. Banks and credit card companies use them to record financial information.Like internal hard disks, hard-disk packs have multiple recording platters aligned one above the other. Hard-disk packs, however, use much larger platters, use more platters, and are not enclosed in a special container. Hard- disk packs are stored in a hard plastic cover that is removed when the pack is mounted onto special drives. The drive rotates the pack and access arms move in and out between the rotating platters. Each access arm has two read/write heads. One reads the disk surface above it; the other reads the disk surface below it. All the access arms move in and out together. However, only one of the read/write heads is activated at a given moment. A disk pack with 11 disks provides 20 recording surfaces. This is because the top and bottom outside surfaces of the pack are not used. (See Figure 8-9.)For a summary of the different types of hard disks, see Figure 8-10.P219PERFORMANCE ENHANCEMENTSThree ways to improve the performance of hard disks are disk caching, redundant arrays of inexpensive disks, and file compression/decompression.Disk caching improves hard-disk performance by anticipating data needs. It performs a function similar to cache memory discussed in Chapter 6. While cache memory improves processing by acting as a temporary high-speed holding area between memory and the CPU, disk caching improves processing by acting as a temporary high-speed holding area between a secondary storage device and the CPU. Disk caching requires a combination of hardware and software. During idle processing time, frequently used data is read from the hard disk into memory (cache). When needed, the data is then accessed directly from memory. The transfer rate from memory is much faster than from the hard disk. As a result, overall system performance is often increased by as much as 30 percent.Redundant arrays of inexpensive disks (RAID) improve performance by expanding external storage, improving access speed, and providing reliable storage. Several inexpensive hard-disk drives are connected to one another. These connections can be by a network or within specialized RAID devices. (See Figure 8-11.) The connected hard-disk drives are related or grouped together, and the computer system interacts with the RAID system as though it were a single large-capacity hard-disk drive. The result is expanded storage capability, fast access speed, and high reliability. For these reasons, RAID is often used by Internet servers and large organizations.File compression and file decompression increase storage capacity by reducing the amount of space required to store data and programs. File compression is not limited to hard-disk systems. It is frequently used to compress files on floppy disks as well. File compression also helps to speed up transmission of files from one computer system to another. Sending and receiving compressed files across the Internet is a common activity.File compression programs scan files for ways to reduce the amount of required storage. One way is to search for repeating patterns. The repeating patterns are replaced with a token, leaving enough tokens so that the original can be rebuilt or decompressed. These programs often shrink files to a quarter of their original size. To learn more about file compression, visit Our Web site at and enter the keyword compression.You can compress and decompress files using specialized utilities such as WinZip from Nico Mak Computing and PKZip from PKWare. Or, if these specialized utilities are not available, you can use utility programs in Windows XP. For a summary of performance enhancement techniques, see Figure 8-12.P220OPTICAL DISCSTodays optical discs can hold over 50 gigabytes of data. (See Figure 8-13.) That is the equivalent of millions of typewritten pages or a medium-sized library all on a single disc. Optical discs sire having a great impact on storage today, but we are probably only beginning to see their effects.In optical-disc technology, a laser beam alters the surface of a plastic or metallic disc to represent data. Unlike floppy and hard disks, which use magnetic charges to represent Is and 0s, optical discs use reflected light. The Is and 0s are represented by flat areas called lands and bumpy areas called pits on the disc surface. The disc is read by an optical disc drive