P213SECONDARY STORAGEIntroductionSecondary storage devices are used to save, to back up, and even to transport file s 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 file s 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 de vices, 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 proce ssed 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 theability to save, or store, information. Asdiscussed in Chapter 6, random-accessmemory (RAM) holds or stores data andprograms that the CPU is presently processing.Before data can be processed or a program canbe run, it must be in RAM. For this reason, RAMis sometimes referred to as pri mary storage.Unfortunately, most RAM provides onlytemporary or volatile storage. That is, it losesall of its contents as soon as the computer isturned off. Its contents also are lost if there is apower failure that disrupts the electric currentgoing into the system unit. This volatilityresults in a need for more permanent ornonvolatile storage for data and programs. W ealso need external storage because users needexternal more storage capacity than is typicallyavailable in a computers primary of RAMmemory.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 devi ces such as a floppy disk drive, data and programs can be retained after the computer has been shut off. This is ac complished by writing files to and reading files from secondary storage devices. W riting 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 de vices.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 devi ces 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。