操作系统课件Chapter1-Introduction

1、Modern Operating Systems Chapter 1 - IntroductionZhang YSpring 2013Content of this lecture1.1 What is an Operating System?1.2 History of Operating Systems1.3 Computer Hardware Review1.4 The Operating System Zoo 1.5 Operating System Concepts1.6 System Calls1.7 Operating System StructureSummary1.1 Wha

2、t is an Operating System?1.2 History of Operating Systems1.3 Computer Hardware Review 1.4 The Operating System Zoo1.5 Operating System Concepts1.6 System Calls1.7 Operating System StructureSummaryWhat is an Operating System?(1)A modern computer consists of One or more processorsMain memoryDisksPrint

3、ersVarious input/output devicesManaging all these components requires a layer of software the operating systemWhat is an Operating System ? (2)An Operating System is a program that acts as an intermediary/interface between a user of a computer and the computer hardware.Figure 1-1. Where the operatin

4、g system fits in.What is an Operating System ? (3)Operating System GoalsConvenience (user goals)Ease of useOften the goal with personal computer systems, i.e., single-user systemsAlso, often the goal with computer novices, and people who dont have a goal of learning more about computersHuman factors

5、 importantEfficiency (system goals)Maximize hardware resource utilizationOften a goal with server systems or “mainframe” computers, i.e., multiple-user systemsAlso, sometimes the goal with computer expertsEasy to design, implement, maintainWhat Is an OS? Real life example?2-3 persons group discussio

6、n2 minutesWhat is an Operating System?(4)The Operating System as an Extended MachineThe OS hides the messy details which must be performed-Provide standard Library (I.e., abstract resources)The OS implements a virtual machine on top of the machine that is easier to use (i.e. write programs for)This

7、is the “top down” (or external view) of an operating system.What is an Operating System?(5)The Operating System as an Extended Machine (ctd.)What is an Operating System?(6)ExampleTo copy bytes from one device (e.g. a CD-ROM to another (e.g. a fixed disk) a programmer must issue several instructions

8、that:Check to see if the device is availableCopy a chunk of bits from the CD-ROM drive into memory Set a status bit to 1 to indicate that there is data in memory that must now be transferred to the disk Generate a signal to the processor to indicate that bytes can now be transferred from memory to t

9、he diskEvery program that needs to carry out this operation would have to include code to do soProgram might have to be modified when devices are changed (e.g. a faster CD-ROM is installed in the computer).What is an Operating System?(7)Example (ctd.)Programming computer hardware directly is difficu

10、ltOperating systems provide a layer between applications and computer hardware:Abstract computer hardware detailsPromote portabilityEnable efficient and safe shared use of hardware resourcesWhat is an Operating System? (8)The Operating System as a Resource ManagerAllow multiple programs to run at th

11、e same timeManage and protect memory, I/O devices, and other resources.Includes multiplexing (sharing) resources in two different ways:In timeIn spaceThis is the “bottom-up” (or internal) view of an OS1.1 What is an Operating System?1.2 History of Operating Systems1.3 Computer Hardware Review1.4 The

12、 Operating System Zoo 1.5 Operating System Concepts1.6 System Calls1.7 Operating System StructureSummaryHistory of Operating Systems (1)Two distinct phases of historyPhase 1: Computers are expensiveGoal: Use computers time efficientlyMaximize throughput (i.e., jobs per second)Maximize utilization (i

13、.e., percentage busy)Phase 2: Computers are inexpensiveGoal: Use peoples time efficientlyMinimize response timeHistory of Operating Systems (2)First Generation 1945 1955 Vacuum tubes, plug boards, punched cards (no OS)Second Generation 1955 1965Transistors, batch systemsThird Generation 1965 1980 IC

14、s, multiprogramming, spooling, timesharingFourth Generation 1980 present Large scale integrationPersonal computers, hand-held devices, sensorsNext Generation?Systems connected by high-speed networks?Wide area resource management?History of Operating Systems (3)First Generation 1945 1955: direct inpu

15、tVacuum tubes, plug boards Machine language,no OSPunched cards(by the early 1950s)Second Generation 1955 1965Transistors, batch systemsMainframe, job (a program or set of programs), FORTRAN or assembler, punched cardsFMS (the Fortran Monitor System), IBSYS (IBMs OS for the 7094)History of Operating

16、Systems (4)History of Operating System (5)Figure 1-3. An early batch system(a) Programmers bring cards to 1401(b) 1401 reads batch of jobs onto tape(c) Operator carries input tape to 7094(d) 7094 does computing(e) Operator carries output tape to 1401(f) 1401 prints outputHistory of Operating Systems

17、 (6)Figure 1-4. Structure of a typical FMS job History of Operating System (7)Second Generation 1955 1965 (ctd.)Goal of OS: Better throughput and utilizationBatch: Group of jobs submitted togetherOperator collects jobs; orders efficiently; runs one at a timeAdvantagesAmortize setup costs over many j

18、obsOperator more skilled at loading tapesKeep machine busy while programmer thinksImproves throughput and utilizationProblemsUser must wait until batch is done for resultsMachine idle when job is reading from cards and writing to printersHistory of Operating Systems (8)Third Generation 1965 1980 ICs

19、, multiprogramming, spooling, timesharingA family of software compatible computers, IBM 360 series, OS/360UniprogrammingProcessor must wait for I/O instruction to complete before precedingHistory of Operating Systems (9)Third Generation 1965 1980 (ctd.)MultiprogrammingWhen one program needs to wait

20、for I/O, the processor can switch to the other programHistory of Operating Systems (10)Third Generation 1965 1980 (ctd.)Multiprogramming (ctd.)Figure 1-5. A multiprogramming system with three jobs in memory Multiple jobs in memory Protected from one another Operating system protected from each job a

21、s well Resources (time, hardware) split between jobs Still not interactive User submits job Computer runs it User gets results minutes (hours, days) laterHistory of Operating Systems (11)Third Generation 1965 1980 (ctd.) SpoolingOriginal batch systems used tape drivesLater batch systems used disks f

22、or bufferingOperator read cards onto disk attached to the computerComputer read jobs from diskComputer wrote job results to diskOperator directed that job results be printed from diskDisks enabled simultaneous peripheral operation on line (spooling)Computer overlapped I/O of one job with execution o

23、f anotherBetter utilization of the expensive CPUStill only one job active at any given timeHistory of Operating Systems (12)Third Generation 1965 1980 (ctd.)TimesharingUsing multiprogramming to handle multiple interactive jobsProcessors time is shared among multiple usersMultiple users simultaneousl

24、y access the system through terminalsCompatible Time-Sharing System (CTSS) First time-sharing system developed at MITMULTiplexed Information and Computing Services (MULTICS)History of Operating Systems (13)Fourth Generation 1980 present Windows is the other Dominant Family of OSCP/M was first PC Ope

25、rating SystemDOS (Disk Operating System) later to be renamed MS-DOS dominated the PC Market.Windows provided GUI for DOS (up to Windows 3.x)Windows 95 was first free standing version of WindowsFollowed by Windows 98Windows NT was first 32-bit OSWindows 2000 was introduced as Windows NT version 4Wind

26、ows VISTAWindows 7History of Operating Systems (14)Fourth Generation 1980 present (ctd.)UnixLinuxCurrent Systems Conclusion: OS changes due to both hardware and usersCurrent TrendsNetworked Operating SystemsDistributed Operating SystemsOS code base is largeMillions of lines of code1000 person-years

27、of workCode is complex and poorly understoodSystem outlives any of its buildersSystem will always contain bugsBehavior is hard to predict, tuning is done by guessing1.1 What is an Operating System?1.2 History of Operating Systems1.3 Computer Hardware Review1.4 The Operating System Zoo 1.5 Operating

28、System Concepts1.6 System Calls1.7 Operating System StructureSummaryA Typical Computer SystemFigure 1-6. Some of the components of a simple personal computer.ProcessorsEach CPU has a specific set of instructionsAll CPUs containGeneral registers inside to hold key variables and temporary resultsSpeci

29、al registers visible to the programmerProgram counter contains the memory address of the next instruction to be fetchedStack pointer points to the top of the current stack in memoryPSW (Program Status Word) contains the condition code bits which are set by comparison instructions, the CPU priority,

30、the mode (user or kernel) and various other control bits.How Processors Work (1)Execute InstructionsCPU CyclesFetch (from mem) decode executeProgram Counter (PC)When is PC changed?Pipeline: fetch n+2 while decode n+1 while execute nSuperscalarHow Processors Work (2)Execute Instructions (ctd.)CPU Cyc

31、les (ctd.)Figure 1-7. (a) A three-stage pipeline. (b) A superscalar CPU.How Processors Work (3)Execute Instructions (ctd.)Two Modes of CPU (why?)User mode (a subset of instructions)Kernel mode (all instruction)Trap (special instruction)Switch from user mode to kernel mode and starts the OSFigure 1-8

32、. (a) A quad-core chip with a shared L2 cache. (Intel)(b) A quad-core chip with separate L2 caches. (AMD)Multithreaded and Multicore ChipsMemory-Storage Hierarchy for command prompt1.1 What is an Operating System?1.2 History of Operating Systems1.3 Computer Hardware Review1.4 The Operating System Zo

33、o 1.5 Operating System Concepts1.6 System Calls1.7 Operating System StructureSummaryFrom Slide What is OSCode that:Sits between programs & hardwareSits between different programsSits betweens different usersJob of OS:Manage hardware resourcesAllocation, protection, reclamation, virtualizationProvide

34、 services to app. How? - System CallAbstraction, simplification, standardizationApplicationOSHardwareA peek into Unix/LinuxApplicationPortable OS LayerLibrariesMachine-dependent layerUser space/levelKernel space/level User/kernel modes are supported by hardware Some systems do not have clear user-ke

35、rnel boundaryUnix: ApplicationApplication (E.g., emacs)Portable OS LayerLibrariesMachine-dependent layerWritten by programmerCompiled by programmerUses function callsUnix: LibrariesApplicationPortable OS LayerLibraries (e.g., stdio.h)Machine-dependent layerProvided pre-compiledDefined in headersInpu

36、t to linker (compiler)Invoked like functionsMay be “resolved” when program is loadedTypical Unix OS StructureApplicationPortable OS LayerLibrariesMachine-dependent layersystem calls (read, open.)All “high-level” codeTypical Unix OS StructureApplicationPortable OS LayerLibrariesMachine-dependent laye

37、rBootstrapSystem initializationInterrupt and exception I/O device driverMemory managementKernel/user mode switchingProcessor managementSystem Calls (1)System CallsThe mechanism used by an application program to request service from the operating system. System calls often use a special machine code

38、instruction which causes the processor to change mode (e.g. to supervisor mode or protected mode). This allows the OS to perform restricted actions such as accessing hardware devices or the memory management unit. System Calls (2)Exampleread (fd, buffer,nbytes)fd: file descriptorbuffer: nbytes: numb

39、er of bytes to readcount=read (fd, buffer,nbytes)Figure 1-17. Steps in Making a System CallSystem Calls (3)POSIXPortable Operating System InterfaceSet of IEEE standardsMandatory + optional partsObjective: Source code portability of applications across multiple OSStandard way for applications to inte

40、rface to OSMostly but not exclusively Unix type OSTotal portability is not achievableThe mapping of POSIX procedure calls onto system calls is not one-to-one.System Calls (4)System Calls for Process Managementfork ()fork is the only way to create a new process in POSIX.The new process created by for

41、k is called the child process.This function is called once but returns twice.Returns: 0 in child, process ID of child in parent, -1 on errorBoth the child and parent continue executing with the instruction that follows the call to fork.System Calls (5)System Calls for Process Management (ctd.)waitpi

42、d()Return: process ID if OK, 0 or 1 on errorThe interpretation of the pid argument depends on its value:pid = = -1 waits for any child process. In this respect, waitpid is equivalent to wait.pid 0 waits for the child whose process ID equals pid.execve()execve function allows child process to execute

43、 code that is different from that of parentexec family of functions provides a facility for overlaying the process image of the calling process with a new image.System Calls (6)System Calls for Process Management (ctd.)Example of fork used in simplified shell program#define TRUE 1while (TRUE) /* rep

44、eat forever */ type_prompt( );/* display prompt */ read_command (command, parameters) /* input from terminal */ if (fork() != 0) /* fork off child process*/ /* Parent code */ waitpid( -1, &status, 0); /* wait for child to exit */ else /* Child code */ execve (command, parameters, 0); /* execute comm

45、and */ System Calls (7)Some System Calls for File Management System Calls (8)Some System Calls for Directory and File System Management System Calls (9)Some System Calls for Directory and File System Management (ctd.)Example: link(“/usr/jim/memo”, “/usr/ast/note”)(a) Two directories before linking/u

46、sr/jim/memo to asts directory(b) The same directories after linkingSystem Calls (10)Some System Calls for Directory and File System Management (ctd.)Example: mount(“/dev/fd0”, “/mnt”,0)(a) File system before the mount(b) File system after the mountSystem Calls (11)Some System Calls for Miscellaneous

47、System Calls (12)The Windows Win32 APIIn windows, the library calls and the actual system calls are highly decoupled.Win32 API for programmers to use to get OS services.The number of Win32 API calls is extremely large, numbering in the thousands.System Calls (13)Some Win32 API calls1.1 What is an Op

48、erating System?1.2 History of Operating Systems1.3 Computer Hardware Review1.4 The Operating System Zoo 1.5 Operating System Concepts1.6 System Calls1.7 Operating System StructureSummaryOperating System Structure (1)Monolithic System - the big mess. All operating system operations are put into a sin

49、gle file. The operating system is a collection of procedures, each of which can call any of the others.Basic StructureA main program that invokes the requested service procedure.A set of service procedures that carry out the system calls.A set of utility procedures that help the service procedures.P

50、roblems: Kernel components arent protected from each other, not easily extended/modified, structure may be unclearOperating System Structure (2)Figure 1-24. Simple structuring model for a monolithic systemOperating System Structure (3)Figure 1-25. Structure of the THE operating systemLayered SystemT

51、he operating system is organized as a hierarchy of layers of processes.Hiding information at each layerDevelop a layer at a timeExample: THE Operating System (Dijkstra, 1968)A simple batch system for Electrologica X8Operating System Structure (4)Layered System (ctd.)Example: MULTICSOperating System

52、Structure (5)MicrokernelsOS kernel is very small minimal functionality.Isolates all hardware dependent and/or policy independent code in the kernel (trusted system)Other OS functions provided at user level by trusted servers.User process, trusted by kernel All policy dependent code is located in use

53、r-space processes (untrusted code)Better Known Microkernels: Integrity, K42, L4, MINIX 3Advantages: maintainability, flexibility, modularityProblems: performanceFigure 1-26. Structure of the MINIX 3 system.Operating System Structure (6)Microkernels (ctd.)Example: MINIX 3Reincarnation ServerOperating

54、 System Structure (7)Microkernels (ctd.)Separation of Policy from MechanismPolicies - What should be doneMechanisms - How it is doneOperating System Structure (8)Client-Server Model Moving most of the code up into the higher layers made the kernel to be minimal and only responsible for communication

55、 between clients and servers.Operating System Structure (9)Client-Server Model (ctd.)The operating system is collection of servers that provide specific services; e.g., file server, etc.Figure 1-27. The client-server model in a distributed systemOperating System Structure (10)Client-Server Model (ctd.)Advantage of this system is adaptability to use in distributed systems