计算机专业英语第八章课文翻译.doc

CHAPTER 8 SECONDARY STORAGEP213 Introduction Secondary 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 of 0s 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。 数据存储已经从文字和数字文件不断扩大，包括数字音乐文件，照相文件，视频文件，以及更多。这些新类型的文件需要有更大容量的辅助存储设备。辅助存储设备一直是在任何计算机系统中不可缺少的元素。他们在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。它们直接发送到内存（RAM），在那里它们可以被 CPU 直接访问和处理。 有能力的终端用户需要认识不同类型的辅助存储器。他们需要了解软盘、硬盘、光盘和辅助存储器的其他类型的容量、限制和使用。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。 P214 STORAGE An 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，因为用户需要更多的外部存储容量,比通常在计算机RAM主内存中可用的多。 Secondary storage provides permanent or nonvolatile storage. Using secondary storage devices such as a floppy disk drive, data and programs can secondary 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 include l Media are the actual physical material that holds the data and programs. (See Figure 8-1.) l Capacity measures how much a particular storage medium can hold. l Storage devices are hardware that reads data and programs from storage media. Most also write to storage media. l 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。 辅助存储的一些重要特征包括 l 介质是保存数据和程序的实际物理材料。（见图 8-1）。 l 容量是测量一个特定的存储介质可以容纳的程度。 l 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。 l 访问速度是测量在存储设备上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。FLOPPY DISKS Floppy 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 1s and 0s. 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。它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。(见图 8-2)P215 TRADITIONAL FLOPPY DISK The traditional floppy disk is the 1.44 MB 2HD 3 1/2-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 意味着两面的，高密度的。双面显示，可以在磁盘双面上存储数据。密度指的是比特（电荷）有多紧密，可以装到另一个。这些磁盘容量为 1.44 兆字节，相当于350 多页打字机纸。软盘有薄的外部硬塑料制成的护套保护灵活磁盘内部。（见图 8-3）。磁盘上的一个快门滑到另一侧可暴露记录的表面。标签为用户提供一个区域来写或磁盘的文档内容。写保护缺口有一个打开和关闭的滑道。在任一位置，文件可从软盘读取。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 and enter the keyword disk. 正如我们在第 5 章讨论的，文件存储和组织在灵活的磁盘，以磁道和扇区为依据。圈形的同心圆环，无可见的凹槽。每个磁道分为无形的楔形部分，称为扇区。每个磁道扇区最多可存储 512 个字节或字符。要看看软盘驱动器如何工作，请访问我们的网站 WWW. ，然后输入关键字磁盘。 HIGH-CAPACITY FLOPPY DISKS High-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磁盒。和传统的软盘一样，高容量磁盘的直径为 3.5 英寸。然而，它们能够存储更多的信息且更厚的，却需要特殊的磁盘驱动器。最广泛使用的高容量磁盘是由 Iomega 生产的Zip 磁盘。这些磁盘通常有 100 MB，250 MB 或 750 MB 容量，超过了现在标准软盘的500倍。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） 。P216 At 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. 有一段时间，软盘足以应付大多数的存储需求，而软盘驱动器则是大多数系统单位的标准功能。 然而，软盘没有容量来存储今天大多数的视频和音乐文件。因此，软盘和软盘驱动器不被广泛使用。HARD DISKS Like 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. 硬盘 和软盘一样，硬盘通过改变磁盘表面的磁荷来保存文件。软盘使用薄的弹性塑料盘，而硬盘使用较厚，刚性金属盘，可以逐个叠在另一个上面。硬盘存储和组织文件会使用磁道，扇区和柱面。一个柱面通过每一个盘片栈的磁道运行。虽然不需要通过带有一个单碟的软盘，但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。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. 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.与软盘相比，硬盘能够存储和检索信息的速度更快，而且有更大的容量。然而，它们是敏感的仪器。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所谓的“迎头相撞”。 （见图 8-5）。 迎头相撞发生在一个读/写头 BK 与硬盘的表面，或在其表面的颗粒接触。迎头相撞是硬盘的灾难。磁盘表面划伤，部分或全部数据会被破坏。曾经，迎头相撞是司空见惯的事。现在，幸运的是，他们是罕见的。硬盘的三种类型：内置硬盘，硬盘磁盒和硬盘组。INTERNAL HARD DISK An 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. 内部硬盘一个内置硬盘位于系统单位。对于大多数微机系统,内置硬盘驱动器被指定为C:驱动器。它是用来存储程序和大型数据文件。例如,几乎每一个微机使用其内置硬盘来存储它的操作系统和主要的应用程序,如Word和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 applications are 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. 内置硬盘有两个优势优于软盘:容量和访问速度。例如，700 g的内置硬盘可以容纳如490000标准软盘几乎一样多的信息。因为硬盘旋转速度和它们的读/写头更接近记录表面,所需查找时间和检索信息(访问速度)比软盘快得多。由于这些原因,几乎所有的今天的强大的应用程序被设计成从内置硬盘存储和运行。想看看一个硬盘如何工作,请访问我们的网站,然后输入关键字磁盘。P217To 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. 确保你的内置硬盘有足够的性能,你应该执行日常维护和定期做所有重要的文件的副本备份。对于硬盘维修和备份过程,请参阅第5章Windows实用程序备份,磁盘清理和磁盘碎片整理程序的报道。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. 硬盘磁盒 虽然内置硬盘提供快速的访问，但是它们有一个固定的存储容量，且不能轻易地从系统内核中移除。硬盘磁盒就像从录像机中取出盒带一样轻松移除。一个计算机系统的存储容量仅限制于磁盒的数量。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. 硬盘磁盒主要用来补充内置硬盘。因为磁盒很容易移除,它们对保护或安全敏感信息特别有用。硬盘磁盒的其他用途包括备份内置硬盘的内容和提供额外的硬盘容量。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.)台式电脑硬盘磁盒的典型容量是20到100 GB 。其中最广泛使用的硬盘磁盒是来自Iomega的可移动硬盘。（见图8-6。）信用卡尺寸的硬盘磁盒叫做PC卡片硬盘，可让笔记本电脑的典型容量增加5 GB。两个著名的PC卡硬盘是IBM的微硬碟机和东芝的MK5002。（见图8-7。）P218 HARDHARD-DISK PACKS Hard-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. 硬盘组 硬盘组是用于存储大量信息的可移动存储设备。(见图8 - 8)。它们的容量远远超过了其他类型的硬盘。尽管你可能从未见过一个,那么几乎可以肯定,你已经在使用它们。微型计算机经常通过通信线路访问外部硬盘组去访问互联网,小型机,或大型机。银行和信用卡公司使用它们来记录财务信息。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.) 像内置硬盘一样,硬盘组有多个上下对齐的记录盘片。然而,硬盘组使用更大的盘片，使用更多的盘片，放在一个不封闭的特殊容器。硬盘组存放在硬塑料盖中，当这个组被安装到特殊的驱动器时，它将被移除。驱动器在旋转的盘片之间使组旋转和接臂移入和移出。每个接臂上有两个读/写磁头。一个读取它上面的磁盘表面，另一个读取它下面的磁盘表面。所有接臂一起移入和移出。然而，在一个给定的时刻只有一个读/写磁头被激活。有11个磁盘的磁盘组提供了20个记录面。这是因为组的外表面的顶部和底部是不使用的。 （见图8-9）For a summary of the different types of hard disks, see Figure 8-10.硬盘的不同类型的总结，见图8-10。P219 PERFORMANCE ENHANCEMENTS Three 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. 性能加强提高硬盘性能的三种方法是磁盘缓存，磁盘阵列，文件压缩/解压。磁盘缓存，通过预测数据的需求提高硬盘的性能。它执行的功能类似于在第6章中讨论的内存缓存。内存缓存提高处理，是通过在内存和CPU之间充当一个临时高速缓冲区，而磁盘缓存提高处理，是通过在辅助存储装置和CPU之间充当一个临时高速缓冲区。磁盘缓存要求硬件和软件的组合。在空闲处理时间，经常使用的数据从硬盘读取到内存（缓存）。当需要时，该数据然后从内存中直接访问。内存的传送速率比从硬盘快得多。结果是，整个系统的性能通常增加30以上。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. 磁盘阵列（RAID）提高性能，通过扩大外部存储设备，提高访问速度和提供可靠的存储。一些廉价的硬盘驱动器被连接到其他。这些连接可以是在一个网络内或专门的RAID设备之间。（见图8-11）相接的硬盘驱动器可以是相关的或组合在一起，计算机系统与RAID系统进行交互，就好像它是一个单一的大容量硬盘驱动器。结果是被扩展的存储能力，快存取速度和高可靠性。由于这些原因，RAID是经常被使用在网络服务器和大型组织。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. 通过减少所需的空间来存储数据和程序，文件压缩与文件解压能增加存储容量。文件压缩并不限于硬盘系统。它也经常可以使用在软盘上压缩文件。文件压缩也可以帮助加快从一台计算机系统到另一台的文件的传输。在互联网上发送和接收压缩文件是一种常见的活动。File compression programs scan files for