中英对照unix操作系统.htm

软考英语精典短文每日一练汇总 软考英语精典短文每日一练汇总

      run on a UNIX host．<BR><BR>2．The UNIX System Can Support Many 
      Users<BR><BR><BR><BR>Depending on the machine being used，a UNIX system can 
      support from one to over one hundred users，each concurrently running a 
      different set of programs．The cost of a computer that can be used by many 
      people at the same time is less per user than that of a computer that can 
      be used by only a single person at a time．[1] The cost is less because one 
      person cannot generally use all of the resources a computer has to 
      offer．No one can keep the printer going constantly，keep all the system 
      memory in use，keep the disk busy reading and writing，keep the tape drives 
      spinning，keep the modem in use，and keep the terminals busy．[2] A multiuser 
      operating system allows many people to use all of the system resources 
      almost simultaneously．Thus，utilization of costly resources can be 
      maximized，and the cost per user can be minimized．These are the primary 
      objectives of a multiuser operating system．<BR><BR>3．The UNIX System Can 
      Support Many Tasks<BR><BR><BR><BR>The UNIX operating system allows each 
      user to run more than one job at a time．You can run several jobs in the 
      background while giving all your attention to the job being displayed on 
      your terminal，and you can ever switch back and forth between jobs．This 
      multitasking capability enables users to be more productive．<BR><BR>4．The 
      UNIX System Kernel<BR><BR><BR><BR>The kernel is the heart of the UNIX 
      operating system，responsible for controlling the computer’s resources and 
      scheduling user jobs so that each one gets its fair share of the 
      resources（including the CPU as well as access to peripheral devices such 
      as disk storage，printers，and tape drives）．Programs interact with the 
      kernel through special functions with well-known names，called system 
      calls．<BR><BR><BR><BR>5．The Shell<BR><BR><BR><BR>The shell is a command 
      interpreter that acts as an interface between users and the operating 
      system．When you enter a command at a terminal，the shell interprets the 
      command and calls the program you want．<BR><BR>Besides its regular 
      function of interpreting commands from a terminal keyboard and sending 
      them to the operating system，the shell can be used as a high-level 
      programming language．Shell commands can be arranged in a file for later 
      execution as a high-level program．This flexibility allows users to perform 
      complex operations with relative ease，often with rather short commands，or 
      to build elaborate programs that perform highly complex operations，with 
      surprisingly little effort．[3]<BR><BR>6．File Structure<BR><BR><BR><BR>A 
      file is a collection of information，such as text for a memo or report， an 
      accumulation of sales figures，or object code created by a compiler．Each 
      file is stored under a unique name，usually on a disk storage device．The 
      UNIX file-system provides a structure where files are arranged under 
      directories，and directories in turn are arranged under other 
      directories，and so forth，in a treelike organization．This structure assists 
      users in keeping track of large numbers of files by enabling them to group 
      related files into directories[4]．Each user has one primary directory and 
      as many subdirectories as required．<BR><BR>7．Device-Independent Input and 
      Output<BR><BR><BR><BR>Devices（such as a printer or terminal）and disk files 
      all appear as files to UNIX programs．When you give the UNIX operating 
      system a command，you can instruct it to send the output to any one of 
      several devices or files．This diversion is called output 
      redirection．<BR><BR>In a similar manner，a program’s input that normally 
      comes from a terminal can be redirected so that it comes from a disk file 
      instead．Under the UNIX operating system，input and output are device 
      -independent；they can be redirected to or from any appropriate 
      device．<BR><BR>As an example，the cat utility normally displays the 
      contents of a file on the terminal screen．When you enter a cat command，you 
      can cause its output to go to a disk file instead of to the 
      terminal．[5]<BR><BR>1．什么是UNIX操作系统<BR><BR>UNIX操作系统最早是由美国电话电报公司（AT&amp;T）贝尔实验室的丹尼斯&#8226;里奇和肯&#8226; 
      汤普森开发的，它允许计算机同时处理多用户和程序。从20世纪70年代开发以来，UNIX经由许多个人和公司，特别是加利福尼亚大学伯克利分校的计算机科学家的努力而得到增强（通常称为伯克利软件发行部UNIX或BSD 
      UNIX）。这种操作系统在各类计算机系统，即从个人计算机到大型机上广泛使用，并可以其他相关形式使用。AIX是运行在IBM工作站上的版本；A/UX是在Macintosh计算机上运行的图形版本；Solaris是在英特尔微处理器上运行的版本；UnixWare是UNIX的Novell实现。UNIX的Net-Ware是可以在UNIX主机上运行的NetWare原始设备制造商（OEM）版本。<BR><BR>2．UNIX系统能支持多用户<BR><BR>与所使用的机器有关，UNIX系统可以支持一个用户到上百个用户，每个用户都并发地运行一组不同的程序。由很多人同时使用一台计算机的人均成本比一次只允许一个人使用一台计算机的成本要低。成本低是因为一个人不能总是使用计算机的所有资源：没有一个人总是占用打印机，占用系统全部内存，总是使磁盘忙于读写，使磁带驱动器一直转动，一直占用modem，总使终端忙碌；一个多用户操作系统允许很多人几乎同时使用所有的系统资源。因此，使昂贵资源的利用率达到最高，户均费用最小，这就是多用户操作系统的主要目标。<BR><BR>3．UNIX系统能支持多任务<BR><BR>UNIX操作系统允许每一个用户每次运行多个作业。可以在后台运行几个作业，同时将全部注意力放在终端正在显示的作业上，甚至还可以在各作业间来回切换。这种多任务能力使用户生产率提高。<BR><BR>4．UNIX系统内核<BR><BR>内核是UNIX操作系统的心脏，它负责控制计算机的资源和调度用户作业，以使人人公平地共享资源（包括CPU以及对磁盘存储器、打印机和磁带驱动器这些外围设备的访问）。程序与内核的交互作用是通过带有熟知名称的专用操作命令实现的，这就称为系统调用。<BR><BR>5．外壳<BR><BR>外壳是一种命令解释程序在用户与操作系统之间充当接口。当你在终端上输入一个命令时，外壳解释该命令并调用你所要的程序。<BR><BR>除了解释来自终端键盘的命令并将其送往操作系统这样的常规操作外，外壳可以作为高级编程语言使用。外壳命令可以安排在一个文件内，以后作为一个高级程序去执行。这种灵活性使用户能用相对容易且通常相当短的一些命令去完成复杂的操作，或者用极小的代价去编写完成极其复杂操作的精细程序。<BR><BR>6．文件结构<BR><BR>文件是信息的汇集，如备忘录或报告的文本，累计的销售数字，或由编译程序生成的目标代码。每个文件存储在惟一名称下，通常存放在磁盘存储器上。<BR><BR>UNIX文件系统提供一种将文件安排在多个目录下的结构，并且这些目录又转而安排在其他目录下等这种树形组织中。这种结构帮助用户通过将相关文件分组到目录中而保有大量的文件。每一用户有一个主目录，需要时可以有多个子目录。<BR><BR>7．与设备无关的输入输出<BR><BR>对于UNIX程序，设备（例如打印机或终端）和磁盘文件都是作为文件出现的。当你给UNIX操作系统一个命令时，可以指挥操作系统把输出送到任何设备或文件上去，这种变更操作称为输出重定向。<BR><BR>用同样的方法，对在正常情况下终端的程序输入也可以重定向，使输入来自磁盘文件。在UNIX操作系统下，输入输出与设备无关，它们可以重定向到或来自任何一种适当的设备。<BR><BR>例如，cat实用程序通常用来在终端屏幕上显示文件的内容。输入cat命令时，可以将文件的内容输出到一个磁盘文件上而不是到终端上。<BR><BR><BR><BR></DIV></TD></TR></TBODY></TABLE>
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