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1、II. How an Os Works Operating systems control different computer processes, such asrunning a spreadsheet program or accessing information from thecomputers memory. One important process is the interpretation ofcommands that allow the user to communicate with the computer. Somecommand interpreters ar

2、e text-oriented, requiring commands to be typedin. Other command interpreters are graphically oriented and let the usercommunicate by pointing and clicking on an icon, an on-screen picture thatrepresents a specific command. Beginners generally find graphicallyoriented interpreters easier to use, but

3、 many experienced computer usersprefer text-oriented command interpreters because they are more powerful.II.操作系统是怎样工作的操作系统控制不同的计算机进程，如运行一个电子表格程序或访问计算机存储器里的信息。一个重要的进程是解释使用户得以与计算机进行通信的命令。有些命令解释器是面向文本的，要求将命令键入。另一些命令解释器是面向图形的，允许用户通过指向并点击图标，即屏幕上代表具体命令的图片，来进行通信。初学者一般觉得面向图形的解释器使用起来容易一些，但是许多有经验的计算机用户更喜欢使用面向

4、文本的命令解释器，因为它们的功能更强大一些。 Operating systems are either single-tasking or multitasking. The moreprimitive single-tasking operating systems can run only one process at atime. For instance, when the computer is printing a document, it cannot startanother process or respond to new commands until the printi

5、ng iscompleted.操作系统或者是单一任务处理的，或者是多任务处理的。早期的单一任务处理操作系统每次仅能运行一个进程。例如，当计算机打印文件时，在打印结束之前，计算机不能开始另一个进程或响应新的命令。 All modern operating systems are multitasking and can run severalprocesses simultaneously. In most computers there is only one centralprocessing unit （CPU）, （the computational and control unit o

6、f the computer）,so a multitasking OS creates the illusion of several processes runningsimultaneously on the CPU. The most common mechanism used to createthis illusion is time-slice multitasking, whereby each process is runindividually for a fixed period of time. If the process is not completedwithin

7、 the allotted time, it is suspended and another process is run. Thisexchanging of processes is called context switching. The OS performs the“bookkeeping” that preserves the state of a suspended process. It also has amechanism, called a scheduler, that determines which process will be runnext. The sc

8、heduler runs short processes quickly to minimize perceptibledelay. The processes appear to run simultaneously because the users senseof time is much slower than the processing speed of the computer.所有现代操作系统都是多任务处理的，可以同时运行数个进程。在大多数计算机中，只有一个中央处理器（CPU）（计算机的计算与控制单元），因此多任务处理操作系统造成一种假象，即数个进程同时在中央处理器上运行。用来

9、造成这种假象的最常见办法是时间片多任务处理，依靠这种方法每个进程都单独运行固定的一段时间。如果进程在分配的时间内没有完成，它即被暂停，而另一个进程开始运行。进程之间的这种切换被称为上下文转换。操作系统进行“簿记”，保存被暂停进程的状态。它还有一种确定下一步运行哪个进程的机制，称之为调度程序。调度程序快速运行短进程，以尽可能缩短可察觉的延迟。由于用户对时间的感觉要比计算机的处理速度慢得多，因此多个进程看似在同时运行。 Operating systems can use virtual memory to run processes thatrequire more main memory tha

10、n is actually available. With this technique,space on the hard drive is used to mimic the extra memory needed.Accessing the hard drive is more time-consuming than accessing mainmemory, however, so performance of the computer slows.interpreter操作系统可以使用虚拟内存，以运行所需主存空间大于实际可用主存空间的进程。使用这种技术，硬盘驱动器上的空间被用来模拟所

11、需的额外内存。然而，访问硬盘驱动器比访问主存耗时多，因此计算机运行起来很慢。III. Current Operating Systems当前的操作系统The operating systems commonly found on personal computers areUNIX, Macintosh OS, MS-DOS, OS/2, and Windows.个人计算机常用的操作系统有UNIX、Macintosh OS、MS-DOS、OS/2以及Windows。1. UNIXUNIX, in computer science, is a multiuser, multitasking op

12、eratingsystem originally developed by Ken Thompson1 and Dennis Ritchie2 atAT&T3 Bell Laboratories4 in 1969 for use on minicomputers. UNIX existsin various forms and implementations; among these are versions developedat the University of California at Berkeley5 （known as BSD6 releases） andversions re

13、leased by AT&T, the most recent being AT&T System V. UNIXis considered a powerful operating system which, because it is written in theC language, is more portableless machine-specificthan other operatingsystems. UNIX is available in several related forms, including AIX, aversion of UNIX adapted by I

14、BM （to run on RISC7-based workstations）,A/UX （a graphical version for the Apple8 Macintosh）, and Mach （arewritten but essentially UNIX-compatible operating system for the NeXTcomputer）.在计算机科学中，UNIX是一种多用户、多任务处理操作系统，最初由肯?汤普森和丹尼斯?里奇于1969年在美国电话电报公司的贝尔实验室里开发，用于小型计算机。UNIX以各种形式和实现方式存在；这其中包括加利福尼亚大学伯克利分校开发的版

15、本（称为“伯克利软件发行中心版本”）和美国电话电报公司发行的版本其最新版本是“美国电话电报公司系统V”。UNIX被认为是一种功能强大的操作系统。因为是用C语言编写的，它比其他操作系统更具有可移植性受机器限制比较少。UNIX还有几个相关的系统形式，包括：AIX，由IBM公司改写的UNIX版本（在基于精简指令集计算机的工作站上运行）；A/UX（用于苹果计算机公司的麦金托什个人计算机上的图形版本）；以及Mach（一种重写的但基本上与UNIX兼容的操作系统，用于NeXT计算机）。Its popularity is due in large part to the growth of the inter

16、connectedcomputer network known as the Internet, the software for which initiallywas designed for computers that ran UNIX. Variations of UNIX includeSunOS （distributed by SUN Microsystems Inc.9）, Xenix （distributed byMicrosoft Corporation）, and Linux 10 . UNIX and its clones supportmultitasking and

17、multiple users. Its file system provides a simple means oforganizing disk files and lets users protect their files from other users. Thecommands in UNIX are not intuitive, however, and mastering the system isdifficult.UNIX的流行，在很大程度上是由于被称作因特网的计算机互联网络的发展，因为因特网使用的软件最初是为运行UNIX的计算机设计的。UNIX的变种包括SunOS（由太阳微

18、系统股份有限公司发布）、Xenix（由微软公司发布）和Linux。UNIX及其克隆产品支持多任务处理和多个用户。其文件系统提供了一种编排磁盘文件的简便方法，并允许用户保护其文件而防范其他用户。然而，UNIX中的命令不很直观，要掌握这个系统比较困难。2. MS-DOSMS-DOS is the acronym for Microsoft Disk Operating System. Incomputer science, MS-DOSlike other operating systemsoversees suchoperations as disk input and output, vide

19、o support, keyboard control, andmany internal functions related to program execution and file maintenance.MS-DOS is a single-tasking, single-user operating system with acommand-line interface.MS-DOS是“微软磁盘操作系统”的首字母缩拚词。在计算机科学中，MS-DOS同其他操作系统一样，管理下面一类的操作：磁盘输入与输出、视频支持、键盘控制以及与程序执行和文件维护有关的许多内部功能。MS-DOS是带有命

20、令行界面的单个任务处理、单用户操作系统。3. OS/2OS/2, or Operating System 2, is an operating system developed for thepersonal computer in the mid-1980s by International Business MachinesCorporation （IBM） and Microsoft Corporation. At the time OS/2 wasintroduced in late 1987, the most common personal computers wereIBM-co

21、mpatible computers running the Microsoft Disk Operating System（MS-DOS） and computers manufactured by Apple Computer Corporationrunning Apples system for the Macintosh （Mac OS）. The Macintoshoperating system included multitasking, a feature that enabled computers torun several applications simultaneo

22、usly. In a computer network,multitasking allows several users on different computers to havesimultaneous access to the same application or data set. OS/2 was the firstoperating system designed for IBM-compatible personal computers thatallowed multitasking.OS/2，或称“第二代操作系统”，是20世纪80年代中期由IBM公司和微软公司为个人计算

23、机开发的一种操作系统。1987年末，OS/2推出时，最常见的个人计算机是运行MS-DOS的IBM兼容机和由苹果计算机公司生产、运行其麦金托什个人计算机操作系统（Mac OS）的计算机。麦金托什个人计算机操作系统包含多任务处理功能，一个使计算机能够同时运行数个应用程序的特征。在一个计算机网络中，多任务处理允许不同计算机上的数个用户同时访问同一个应用程序或数据集。OS/2是为IBM兼容个人计算机设计、允许多任务处理的第一个操作系统。 The first version of OS/2, version 1.0, was text-oriented and lacked agraphical use

24、r interface （GUI） that would allow users to enter commandswith a point-and-click input device, such as a computer mouse. A year laterIBM and Microsoft released OS/2 version 1.1, which included a GUI calledthe Presentation Manager. The Presentation Manager interface containedicons, pictures or words

25、on the screen that users could click on with amouse to enter instructions. OS/2 version 1.1 also allowed users to havemultiple windows open （windows are portions of the screen that eachcontain a different document or program） and included pull-down lists ofcommands that the user could choose by clic

26、king on them with their mouse.OS/2的第一个版本，1.0版本，是面向文本的，没有允许用户通过使用计算机鼠标等指向与点击输入设备来输入命令的图形用户界面（GUI）。一年后，IBM和微软发布了OS/2的1.1版本，它包括一个称为表示管理程序的图形用户界面。表示管理程序界面包含图标，亦即屏幕上用户可以用鼠标点击来输入指令的图片或文字。OS/2的1.1版本也允许用户打开多个窗口（窗口是屏幕上的一个部分，每个窗口包含一个不同的文件或程序），并包括用户可以用鼠标点击来进行选择的下拉式命令清单 IBM and Microsoft ended their collaborati

27、on on OS/2 in 1991 afterMicrosoft released its Windows software, a multitasking environment thatran on MS-DOS. In 1992 IBM released version 2.0 of OS/2, which ranMicrosoft Windows programs and could perform multitasking of DOSoperations. It also contained an object-oriented programming environmentth

28、at allowed software designers to create programs using high-level,object-oriented programming languages.1991年，在微软发布了Windows软件在MS-DOS上运行的多任务处理环境之后，IBM和微软结束了它们在OS/2上的合作。1992年，IBM发布了OS/2的2.0版本。该版本运行微软的Windows程序，并可以执行DOS操作下的多任务处理。它也包含面向对象的编程环境，允许软件设计者使用高级的面向对象编程语言编程。 Subsequent versions of OS/2 offered

29、enhanced performance andmultimedia capabilities, and in 1994 IBM announced that more than 5million copies of OS/2 had been sold since its introduction. The same year,IBM introduced a new version of OS/2 called OS/2 Warp that featuredimproved performance, more multimedia capabilities, an array ofinte

30、grated applications, and easy access to the Internet. IBM has continuedto upgrade and extend OS/2 Warp.OS/2后来的版本增强了性能和多媒体能力。1994年，IBM宣布，自OS/2推出后已售出5百多万份。同一年，IBM推出OS/2的一个新版本，称为OS/2 Warp。其特色为：改善的性能、增强的多媒体能力、一系列的集成应用程序和方便的因特网接入。IBM公司继续对OS/2 Wrap进行升级和扩充。4. Windows Windows, in computer science, is a personal computer operatingsystem sold by Microsoft Corporation that allows users to enter commandswith a point-and-click device, such as a mouse, instead of a keyboard.