1、計算機操作系統主講教師：主講教師： 劉詠梅劉詠梅 白翔宇白翔宇 斯勤夫斯勤夫內蒙古大學計算機學院內蒙古大學計算機學院計算機操作系統參考書：1、計算機操作系統（湯子瀛著）西安電子科技大學2、現代操作系統（陳向群譯）機械工業出版社3、操作系統精髓與設計原理（William Stallings著）清華大 學出版社4、實用操作系統概念（Abraham Silberschatz著） 高等教育 出版社5、 操作系統原理教程（孟靜著）清華大學出版社第一章第一章 操作系統引論操作系統引論1.1 1.1 什么是操作系統什么是操作系統1.2 1.2 操作系統的發展操作系統的發展1.3 1.3 操作系統的特征和功能

2、操作系統的特征和功能1.4 1.4 操作系統的結構操作系統的結構1.1 什么是操作系統什么是操作系統一、計算機系統組成一、計算機系統組成 中央處理機（中央處理機（CPU） 硬件硬件 內存內存 I/O設備設備（鍵盤、顯示器、打字機、鼠標） 外部設備外部設備 存儲設備存儲設備（硬盤、軟盤、光盤、磁帶） 其它設備其它設備（MODEM、通信口） 系統軟件系統軟件（操作系統、Turbo-C、數據庫管理系統） 軟件軟件 應用軟件應用軟件 （CAD、游戲、用戶自己開發的系統等） 一個現代計算機系統CPU磁盤磁盤驅動器驅動器打印機打印機驅動器驅動器磁帶磁帶驅動器驅動器存儲器驅動器存儲器驅動器 磁盤磁盤 磁盤磁

3、盤打印機打印機磁帶磁帶存儲器存儲器系統總線系統總線1.1 什么是操作系統什么是操作系統二、操作系統在計算機系統中的地位二、操作系統在計算機系統中的地位應用軟件應用軟件其它系統軟件其它系統軟件操作系統操作系統計算機硬件（裸機）計算機硬件（裸機） 操作系統的地位：操作系統的地位： 配置在硬件之上的配置在硬件之上的第一層軟件；第一層軟件； 對硬件功能的第一對硬件功能的第一次擴充。次擴充。1.1 什么是操作系統什么是操作系統應用軟件應用軟件其它系統軟件其它系統軟件操作系統操作系統計算機硬件（裸機）計算機硬件（裸機）普通用戶普通用戶操作系統操作系統開發人員開發人員三、用戶使用操作系統的途徑三、用戶使用操

4、作系統的途徑1.1 什么是操作系統什么是操作系統 1. 方便性：使計算機系統更容易使用。 2. 有效性：提高計算機系統的資源利用率； 提高系統的吞吐量。 3. 可擴充性：允許改進老的功能及增加新的功能。 四、設置操作系統的目標四、設置操作系統的目標1.1 什么是操作系統什么是操作系統五、操作系統的作用五、操作系統的作用 v 作用作用1(1(服務服務):):操作系統是用戶與計算機硬件系統之間的接口。操作系統是用戶與計算機硬件系統之間的接口。操作系統為用戶和程序員提供的服務：操作系統為用戶和程序員提供的服務： 1.負責程序的創建、啟動、執行和結束處理。 2.訪問I/O設備。 3.控制文件存取。 4

5、.通信。 5.差錯檢測。接口類型：接口類型： 1.命令接口：例如DOS命令。 2.程序接口：即系統調用，例如編程中使用的read命令。 3.圖形接口：例如WINDOWS圖標。1.1 什么是操作系統什么是操作系統包括：包括： 1.CPU管理； 2.存儲器管理； 3.I/O設備管理； 4.文件管理。五、操作系統的作用五、操作系統的作用 v 作用作用2(2(管理管理) )：操作系統是計算機系統的資源管理者，它負責 計算機系統的全部資源的分配、控制、調度和回收。1.1 什么是操作系統什么是操作系統五、操作系統的作用五、操作系統的作用 v作用作用3(3(虛擬機) )：操作系統隱蔽硬件特性，為用戶提供了一

6、臺等 價的擴充機器（虛擬機）。虛擬機：虛擬機：覆蓋了軟件、功能變得更加強大的機器。例：只能做加法的機器（只能做加法的機器（+ +）2+325先轉成先轉成2+2+2+2+2實現乘法的軟件（實現乘法的軟件（+ +和和 ）直接做直接做直接做直接做直接做直接做1.1 什么是操作系統什么是操作系統一是自頂向下、從用戶的角度看；（作用一是自頂向下、從用戶的角度看；（作用1、3） 一是自底向上、從硬件的角度看。（作用一是自底向上、從硬件的角度看。（作用2）面對用戶、面對機器面對用戶、面對機器1.1 什么是操作系統什么是操作系統操作系統定義：操作系統定義： 操作系統是一組控制和管理計算機硬件和軟件操作系統是一

7、組控制和管理計算機硬件和軟件資源、合理地對各類作業進行調度，以及方便用資源、合理地對各類作業進行調度，以及方便用戶的程序的集合。戶的程序的集合。1.2 操作系統的發展操作系統的發展發展原因：發展原因：內因：受計算機硬件發展的驅動。外因：受計算機應用的刺激。 與計算機系統發展同步與計算機系統發展同步1.2 操作系統的發展操作系統的發展一、無操作系統時的計算機系統一、無操作系統時的計算機系統工作過程：工作過程： 用戶1：紙帶 紙帶輸入機 計算機 紙帶輸出機 紙帶 用戶2：工作方式：工作方式： 編程語言：機器語言。 輸入輸出：紙帶或卡片。 用戶：既是程序員，又是操作員；是計算機專業人員。1.2 操作

8、系統的發展操作系統的發展一、無操作系統時的計算機系統一、無操作系統時的計算機系統特點：特點： 1.用戶獨占全機：不出現資源被其他用戶占用的情況， 資源利用率低； 2.CPU等待用戶：計算前后，手工裝卸紙帶或卡片； CPU利用率低。造成：1、人機矛盾； 2、CPU與I/O設備 速度不匹配的矛盾。 -CPU浪費嚴重!專門的操作員；批處理。1.2 操作系統的發展操作系統的發展二、單道二、單道批處理系統（批處理系統（Simple Batch System）工作過程：工作過程： 程序員將各自的作業提交給系統操作員，系統操作員采用脫機輸入方式將多個作業組織成一批，輸入磁帶。在系統中配置有監督程序，它從磁帶

9、上讀入第一個作業并運行，其輸出寫到另一個磁帶；每個作業結束后，監督程序自動從磁帶上讀入下一個作業并運行。當這批作業全部結束后，系統操作員再采用脫機輸出技術將保存在磁帶上的結果打印，交給相應的程序員。提交的作業包括提交的作業包括：用戶程序、數據和作業說明書（作業控制語言） 關鍵 脫機輸入輸出技術 監督程序：現代操作系統的前身，常駐內存 job1job2job3job4主機主機監督程序監督程序輸入設備輸入設備外圍機外圍機磁盤磁盤磁盤磁盤輸出設備輸出設備程序員程序員操作員操作員外圍機外圍機job1job2job3job4job1job2job3job41.2 操作系統的發展操作系統的發展二、單道二、

10、單道批處理系統（批處理系統（Simple Batch System）工作方式：工作方式： 編程語言：匯編語言、FORTRAN語言。 輸入輸出：磁帶。 用戶：第一次在程序員、操作員和維護員之間有了明確的分工。進步之處：進步之處： 減少了CPU的空閑時間、提高了I/O速度，從而提高了 CPU的利用率。不足之處：不足之處： I/O速度仍顯慢，使CPU許多時間空閑；無交互能力。1.2 操作系統的發展操作系統的發展三、多道批處理系統三、多道批處理系統（Multiprogramming Batch SystemMultiprogramming Batch System）與單道批處理系統的區別：與單道批處理

11、系統的區別： 輸入輸出：磁盤，spooling技術（聯機）。 操作系統：使用多道程序技術處理作業。優點：優點： 1.資源利用率高； 2.系統吞吐量大。缺點：缺點： 1.平均周轉時間長； 2.無交互能力1.2 操作系統的發展操作系統的發展多道程序技術：多道程序技術：多道：計算機內存中同時存放幾個用戶作業；宏觀上并行運行：內存中的幾個作業都處于運行狀態， 但都未運行完；微觀上串行運行：內存中的各作業交替使用CPU；可共享計算機系統中的各種軟、硬件資源。例：作業A和B在單道和多道系統下的運行對比。job1job2job3job4主機主機監督程序監督程序單道系統單道系統job1job2job3job4

12、主機主機監督程序監督程序多道系統多道系統job1job1job2job2job3job3job4job4job1job3job3job2job4job1job4job2 t1 t2 t3 t4 t5 t6 t7 t8 t9時間時間輸入機輸入機CPU打印機打印機 磁帶機磁帶機時間時間輸入機輸入機CPU打印機打印機 磁帶機磁帶機BAAAAAABBAAAAABBB單單道道多多道道1.2 操作系統的發展操作系統的發展四、分時系統（四、分時系統（Time-sharing System）工作方式：工作方式： 一臺計算機連接多個用戶終端，允許多個用戶共享計 算機中的資源，每個用戶可通過各自的終端以交互方式

13、使用計算機。分類：分類： 1.單道分時系統 2.具有“前臺”和“后臺”的分時系統 3.多道分時系統1.2 操作系統的發展操作系統的發展四、四、分時系統（分時系統（Time-sharing System）特點：特點： 1.多路性 2.獨立性 3.及時性 4.交互性 1.2 操作系統的發展操作系統的發展五、五、實時系統（實時系統（Real-time System）實時系統：實時系統：系統能及時響應外部事件的請求，在規定的時間內 完成對該事件的處理，并控制所有實時任務協調一致地運行。分類：分類： 1.實時控制：例如飛機自動駕駛系統、工業控制等 2.實時信息處理：例如圖書管理系統、民航售票系統等特點：

14、特點： 1.多路性 2.獨立性 3.及時性 4.交互性 5.可靠性 1.2 操作系統的發展操作系統的發展六、六、微機操作系統微機操作系統應用領域：應用領域：事務處理，個人娛樂；系統要求：系統要求：使用方便、支持多種硬件和外部設備（多媒體設備、 網絡、遠程通信）、效率不必很高。常用的個人計算機操作系統：常用的個人計算機操作系統： 1.單用戶單任務：CP/M、MS-DOS 2.單用戶多任務：OS/2、MS Windows 3.多用戶多任務：UNIX1.2 操作系統的發展操作系統的發展七、網絡操作系統（七、網絡操作系統（Network Operating System）計算機網絡：計算機網絡：一些自

15、主的計算機系統，通過通信設施相互連接， 完成信息交換、資源共享、互操作和協同工作等功能。計算機網絡類型：計算機網絡類型： 1.按網絡拓撲：星形、樹形、總線形、環形、網狀形； 2.按地理范圍：局域網、廣域網；1.2 操作系統的發展操作系統的發展七、七、網絡操作系統（網絡操作系統（Network Operating System）網絡網絡OS：根據已有標準開發出的、具有支持網絡資源通信、共 享和管理等功能的軟件模塊和原有網絡計算機系統中 操作系統的合稱。網絡網絡OS功能：功能： 1.通常操作系統的功能 2.網絡通信功能 3.網絡資源管理 4.網絡服務 5.網絡管理 6.互操作能力1.2 操作系統的

16、發展操作系統的發展八、八、分布式操作系統（分布式操作系統（Distributed System）分布式系統：分布式系統：指由多個分散的處理單元，經互連網絡的連接而 形成的系統。它的基本特征是處理上的分布，即 資源、功能、任務和控制的分布。分布式操作系統：分布式操作系統：所有系統任務可在系統中任何處理機上運行， 自動實現全系統范圍內的任務分配并自動調度各 處理機的工作負載。1.2 操作系統的發展操作系統的發展分布式分布式OS與網絡與網絡OS的比較的比較分布式分布式OS網絡網絡OS分布性分布性處理分布、控制分布處理分布、控制分布處理分布、控制集中處理分布、控制集中并行性并行性有任務分配功能，任務有

17、任務分配功能，任務可并行執行可并行執行無任務分配功能無任務分配功能透明性透明性網絡資源調度對用戶透網絡資源調度對用戶透明明網絡資源的使用由用戶直網絡資源的使用由用戶直接指定接指定共享性共享性所有資源可供系統中所所有資源可供系統中所有用戶共享有用戶共享可共享資源大多設置在服可共享資源大多設置在服務器上務器上健壯性健壯性強強弱弱1.2 操作系統的發展（小結）操作系統的發展（小結）第一代第一代第二代第二代第三代第三代第四代第四代1945-19551955-19651965-19801980至今電子管晶體管集成電路超大規模集成電路無操作系統；無程序設計語言；采用手工操作方式單道批處理系統；FORTRA

18、N、匯編語言；多道批處理系統；分時系統；實時系統；多道程序設計技術；spooling技術；中斷、通道、DMA、虛存、設備獨立性；微機操作系統；網絡操作系統；分布式操作系統；Knot tying is one of the oldest skills known to man. Many thousands of different knots exist; these are some of the most common.Common Knots早期的計算工具早期的計算工具 - 計算尺計算尺 Blaise Pascal（布里斯（布里斯.帕斯卡）制造的世界上第一臺機械計算機帕斯卡）制造的世界上

19、第一臺機械計算機Pascals Calculator In 1642, Blaise Pascal developed a mechanical calculator to speed arithmetic calculations for his father, a tax official. Numbers are dialed in on the metal wheels on the front of the calculator. The solutions appear in the little windows along the top.Pascals Calculator 世

20、界上第一臺差分機械計算機的發明人查爾斯世界上第一臺差分機械計算機的發明人查爾斯.巴貝奇巴貝奇Inventor of the Difference Engine, British mathematician Charles Babbage is credited with conceiving the first true computer. With the help of his partner, Augusta Ada Byron, Babbage also created a design for the Analytical Engine, another machine remark

21、ably like the modern computer, even including a memory. Unfortunately, there was no way to build the machine with 19th-century technology.Charles BabbageCharles Babbage （查爾斯（查爾斯.巴貝奇）發明的世界上第一臺差分機械計算機巴貝奇）發明的世界上第一臺差分機械計算機Considered by many to be a direct forerunner of the modern computer, the Differenc

22、e Engine was able to compute mathematical tables. This woodcut shows a small portion of the ingenious machine, which was designed by Charles Babbage in the 1820s. Although the device did not have a memory, Babbages later idea for the Analytical Engine would have been a true, programmable computer if

23、 the technology of his time had been able to build it.Babbages Difference Engine早期電子真空管早期電子真空管 A model of the Fleming valve illustrates the technology that led to the development of the vacuum tube, one of the most important early electronic devices. A typical vacuum tube consists of electrodes (met

24、al plates) and wires in an evacuated glass bulb and is used to regulate electric currents or electronic signals. Before the advent of the transistor, vacuum tubes were used extensively in the operation of devices such as televisions, radios, and computers. Sir John Ambrose Fleming experimented with

25、Edisons diode vacuum tube (an invention Edison did not pursue) during the early 1900s, and his valves represent the first practical radio tubes.Early Vacuum Tubes半導體集成電路板集成電路板集成電路板集成電路板集成電路板計算機中的集成電路計算機中的集成電路計算機中的集成電路芯片計算機中的集成電路芯片- CPUThe Pentium microprocessor (shown at 2.5X magnification) is manuf

26、actured by the Intel Corporation. It contains more than three million transistors. The most common semiconductor materials used in making computer chips are the elements silicon and germanium, although nearly all computer chips are made from silicon.奔騰處理機Pentium(放大 2.51,000,000倍)Intel Pentium處理器全家福處

27、理器全家福In 1965 semiconductor pioneer Gordon Moore predicted that the number of transistors contained on a computer chip would double every year. This is now known as Moores Law, and it has proven to be somewhat accurate. The number of transistors and the computational speed of microprocessors currentl

28、y doubles approximately every 18 months. Components continue to shrink in size and are becoming faster, cheaper, and more versatile.Gordon Moores Law戈登戈登.摩爾定律摩爾定律Early United States censuses were tabulated by hand, a process that took years. The electric tabulating machine, invented by American engi

29、neer Herman Hollerith and first used in the 1890 U.S. census, dramatically reduced the time and effort required to process census data. To use the machine, census clerks converted responses on census questionnaires to holes punched in predetermined locations on paper cards. When pins in the card rea

30、der passed through the holes, an electrical circuit was completed that activated the appropriate mechanical counters.Electric Tabulating Machine穿孔卡片機械的早期創始人穿孔卡片機械的早期創始人赫爾曼赫爾曼.赫爾里希赫爾里希American inventor Herman Hollerith developed the punch card system of recording data, an important step in the develo

31、pment of computers. In 1896 he organized the Tabulating Machine Corporation, which became the International Business Machines Corporation (IBM) in 1924.Herman HollerithENIAC (Electronic Numerator, Integrator, And Computer) was the first fully electronic digital computer. Built at the University of P

32、ennsylvania in 1946, it remained in service until 1955. ENIAC contained 18,000 vacuum tubes and required manual rewiring to be programmed.世界上第一臺電子計算機世界上第一臺電子計算機 - ENIAC 世界上第一臺商用電子數字計算機世界上第一臺商用電子數字計算機UNIVACUNIVAC Computer System The first commercially available electronic computer, UNIVAC I, was also

33、 the first computer to handle both numeric and textual information. Designed by John Presper Eckert, Jr., and John Mauchly, whose corporation subsequently passed to Remington Rand, the implementation of the machine marked the beginning of the computer era. Here, a UNIVAC computer is shown in action.

34、 The central computer is in the background, and in the foreground is the supervisory control panel. Remington Rand delivered the first UNIVAC machine to the U.S. Bureau of Census in 1951.早期計算機的輸入設備早期計算機的輸入設備Card Key Punch（穿孔卡片機）（穿孔卡片機）數據處理領域的先驅者Grace Hopper(格里斯.胡泊)(女)A pioneer in data processing, Re

35、ar Admiral Grace Hopper received credit for creating the first compiler in 1952. Hopper helped to develop two computer languages and to make computers attractive to businesses. One of the most prominent women in the computer industry, Hopper died in 1992.In 1964 International Business Machines Corpo

36、ration (IBM) introduced its revolutionary System/360, the first mainframe computer that used interchangeable software and equipment. During the 1960s and 1970s IBM dominated the world market for mainframe computers.60年代的IBM-360(大型計算機)Steven Jobs（史迪瓦（史迪瓦.喬布斯）和喬布斯）和他的蘋果計算機他的蘋果計算機APPLE IIApple Computer

37、 cofounder Steven Jobs, left, CEO John Sculley, center, and cofounder Stephen Wozniak, right, are shown at the 1984 debut of the Apple IIc computer, which was introduced in the same year as the revolutionary Macintosh computer. All three played crucial roles in developing and marketing computers tha

38、t are easy to learn and use. Men Behind Apple Computer蘋果計算機的創始人之一蘋果計算機的創始人之一Steven Jobs（史迪夫（史迪夫.喬布斯）喬布斯）Steven Jobs, with Apple cofounder Steve Wozniak, built the first Apple computer in his parents garage. Apple Computer went on to become the fastest-growing company in American history. In 1985, af

39、ter developing the original Apple Macintosh, Jobs resigned to form NeXT, Inc. His innovative designs have proven technologically superior but prohibitively expensive and are often considered to be too far ahead of their time.蘋果計算機的創始人之一蘋果計算機的創始人之一John Sculley（約翰（約翰.斯庫李）斯庫李）John Sculley started as a

40、trainee at PepsiCo in 1967 and became the companys president ten years later. In 1983 he was recruited to Apple Computer by cofounder Steven Jobs. As chief executive officer (CEO) of Apple, Sculley oversaw further development of the Macintosh computer and the introduction of the System 7 operating s

41、ystem and the Newton, a personal digital assistant. He was replaced as the CEO in 1993 and resigned from the company later that year.The Apple Macintosh, released in 1984, was among the first personal computers to use a graphical user interface. A graphical user interface enables computer users to e

42、asily execute commands by clicking on pictures, words, or icons with a pointing device called a mouse.1984年的蘋果計算機年的蘋果計算機Apple MacintoshBill Gates is the chairman, chief software architect, and cofounder (with Paul Allen) of Microsoft Corporation, the worlds leading computer software company. The com

43、panys success made Gates one of the worlds richest people.Bill Gates微軟具有代表意義的圖形界面操作系統微軟具有代表意義的圖形界面操作系統Windows 95A typical personal computer has components to display and print information (monitor and laser printer); input commands and data (keyboard and mouse); retrieve and store information (CD-RO

44、M and disk drives); and communicate with other computers (modem).Personal Computer Components早期機械打字機早期機械打字機The AT keyboard is an 84-key model introduced by IBM. An attempt to make the personal computer (PC) keyboard more suited to touch-typing, its layout is similar to that of a standard typewriter.

45、AT KeyboardThe IBM enhanced keyboard features several options not used in earlier models. Additions include 12 function keys across the top (versus 10 down the side), additional Control and Alt keys, and a bank of cursor-movement and editing keys between the main section of the keyboard and the nume

46、ric keypad.Enhanced Keyboard機械鼠標的內部結構機械鼠標的內部結構Hard disks are used to record computer data magnetically. A hard disk drive consists of a stack of inflexible magnetic disks mounted on a motor. As the disks spin at high speeds, read/write heads at the end of a metal fork swing in and out to access sect

47、ors of the disks.硬磁盤的結構硬磁盤的結構The concept of the paperless e-book became a reality in the late 1990s with the marketing of several devices. These machines allow users to download texts from the Internet and read them on a portable, handheld display. The RCA REB1100 model e-book shown here is about th

48、e size of a paperback. It lasts 20 to 40 hours between battery charges, holds a minimum of 8,000 pages of text, and includes an internal modem for downloading books.E-Book世界上功能最強大的超級計算機CRAY（克雷機）The Cray-2 Supercomputer (designed by Seymour Cray of Cray Research, Eagan, MN) was first introduced in 19

49、85, nine years after the first model, the Cray-1, was introduced. This type of supercomputer is used for mathematical studies of very complex problems, such as speech analysis, weather forecasting, and fundamental questions in physics and chemistry.Cray Supercomputer著名的國際象棋大師Kasparov與IBM的超級計算機Deep B

50、lue(深藍)下棋Inernet(互聯網互聯網)計算機網絡計算機網絡計算機網絡的結構Connecting individual computers to each other creates networks. The Internet is a series of interconnected networks. Personal computers and workstations are connected to a Local Area Network (LAN) by either a dial-up connection through a modem and standard p

51、hone line or by being directly wired into the LAN. Other modes of data transmission that allow for connection to a network include T-1 connections and dedicated lines. Bridges and hubs link multiple networks to each other. Routers transmit data through networks and determine the best path of transmi

52、ssion.Computer Network Timothy Berners-Lee British computer scientist, developed the World Wide Web during the 1980s.萬維網的創始人萬維網的創始人 Timothy Berners-Lee 現代計算機體系結構的創始人John von Neumann（約翰.馮.諾伊曼）A brilliant mathematician, John von Neumann made several valuable contributions to 20th-century science. The

53、best known of these was the development of game theory, a mathematical way to analyze a conflict of interest and generate the best choices to advance toward a desired outcome. Although it is generally applied to games, many people apply Neumanns theory to sociological, economic, and political situat

54、ions.Alan Turing(愛倫.圖靈) 現代理論計算機體系結構的創始人Considered a forerunner in the field of electronic computers, Alan Turing envisioned a device that could, in theory, perform any calculation. Referred to as the Turing Machine, it was designed to “read” commands and data from a long piece of tape, using a table

55、 to determine the order in which the required operations would be carried out. In the related field of artificial intelligence, he originated the “Turing test” a process designed to determine if a computer can “think” like a human.Alan Turing1.3 操作系統特征和功能操作系統特征和功能一、操作系統的特征一、操作系統的特征1. 并發性（并發性（Concurr

56、ence） 并行性：并行性：兩個或多個事件在同一時刻發生。 并發性：并發性：兩個或多個事件在同一時間間隔內發生。并行是一種微觀的同時性概念。并發是一種宏觀上的同時性概念：宏觀上并發，微觀 上交替占用CPU運行。為更好描述并發性，引入進程概念。 t1 t2 t3 t4 t5 t6 t7 t8 t9時間時間輸入機輸入機CPU打印機打印機 磁帶機磁帶機時間時間輸入機輸入機CPU打印機打印機 磁帶機磁帶機BAAAAAABBAAAAABBB單單道道多多道道1.3 操作系統特征和功能操作系統特征和功能一、操作系統的特征一、操作系統的特征2.2.共享共享（Sharing） 共享：共享：指計算機系統中的各種軟、硬件資源可供內存中 多個并發運行的進程共同使用。 方式方式： 互斥共享：例打印機 同時訪問：例磁盤文件 （注：“同時”也是宏觀上的同時）1.3 操作系統特征和功能操作系統特征和功能一、操作系統的特征一、操作系統的特征3.3.虛擬虛擬（Virtual） 虛擬：虛擬：通過某種技術將一個物理實體變為若干個邏輯上 的對應物。 例：CPU -分時系統 多個CPU 前者真實存在；后者只是用戶的感覺。4.4.異步性（異步性（Asynchronism） 異步性異步性：也稱不確定性，指進程的執行