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1、Chapter 2:Operating-System Structures,Chapter Objectives,View OS from:ServicesInterfacesComponents and InterconnectionsTo describe the services an operating system provides to users,processes,and other systemsTo discuss the various ways of structuring an operating systemTo explain how operating syst
2、ems are installed and customized and how they boot,Content Overview,Operating System ServicesUser Operating System InterfaceSystem CallsTypes of System CallsSystem ProgramsOperating System Design and ImplementationOperating System StructureVirtual MachinesOperating System GenerationSystem Boot,2.1 O
3、perating System Services,One set of operating-system services provides functions that are helpful to the user:User interface-Almost all operating systems have a user interface(UI)Varies between Command-Line(CLI),Graphics User Interface(GUI),Batch programming interfaceProgram execution-The system mus
4、t be able to load a program into memory and to run that program,end execution,either normally or abnormally(indicating error)I/O operations-A running program may require I/O,which may involve a file or an I/O device.File-system manipulation-The file system is of particular interest.Obviously,program
5、s need to read and write files and directories,create and delete them,search them,list file Information,permission management.,Operating System Services(Cont.),One set of operating-system services provides functions that are helpful to the user(Cont):Communications Processes may exchange information
6、,on the same computer or between computers over a networkCommunications may be via shared memory or through message passing(packets moved by the OS)Error detection OS needs to be constantly aware of possible errorsMay occur in the CPU and memory hardware,in I/O devices,in user programFor each type o
7、f error,OS should take the appropriate action to ensure correct and consistent computingDebugging facilities can greatly enhance the users and programmers abilities to efficiently use the system,Operating System Services(Cont.),Another set of OS functions exists for ensuring the efficient operation
8、of the system itself via resource sharingResource allocation-When multiple users or multiple jobs running concurrently,resources must be allocated to each of themMany types of resources-Some(such as CPU cycles,mainmemory,and file storage)may have special allocation code,others(such as I/O devices)ma
9、y have general request and release code.Accounting-To keep track of which users use how much and what kinds of computer resourcesProtection and security-The owners of information stored in a multiuser or networked computer system may want to control use of that information,concurrent processes shoul
10、d not interfere with each otherProtection involves ensuring that all access to system resources is controlledSecurity of the system from outsiders requires user authentication,extends to defending external I/O devices from invalid access attemptsIf a system is to be protected and secure,precautions
11、must be instituted throughout it.A chain is only as strong as its weakest link.,2.2 User Operating System Interface,CLI(Command Line Interface)allows direct command entrySometimes implemented in kernel,sometimes by systems programSometimes multiple flavors implemented shellsPrimarily fetches a comma
12、nd from user and executes itSometimes commands built-in,sometimes just names of programsIf the latter,adding new features doesnt require shell modification,User Operating System Interface-GUI,User-friendly desktop metaphor interfaceUsually mouse,keyboard,and monitorIcons represent files,programs,act
13、ions,etcVarious mouse buttons over objects in the interface cause various actions(provide information,options,execute function,open directory(known as a folder)Invented at Xerox PARC 1970sMany systems now include both CLI and GUI interfacesMicrosoft Windows is GUI with CLI“command”shellApple Mac OS
14、X as“Aqua”GUI interface with UNIX kernel underneath and shells availableSolaris is CLI with optional GUI interfaces(Java Desktop,KDE),2.3 System Calls,Programming interface to the services provided by the OSTypically written in a high-level language(C or C+)Mostly accessed by programs via a high-lev
15、el Application Program Interface(API)rather than direct system call useThree most common APIs are:Win32 API for Windows,POSIX API for POSIX-based systems(including virtually all versions of UNIX,Linux,and Mac OS X),and Java API for the Java virtual machine(JVM),Example of System Calls,System call se
16、quence to copy the contents of one file to another file,Why use APIs rather than system calls?Program portability/convenience/,Example of Standard API,Consider the ReadFile()function in the Win32 APIa function for reading from a fileA description of the parameters passed to ReadFile()HANDLE file the
17、 file to be readLPVOID buffer a buffer where the data will be read into and written fromDWORD bytesToRead the number of bytes to be read into the bufferLPDWORD bytesRead the number of bytes read during the last readLPOVERLAPPED ovl indicates if overlapped I/O is being used,System Call Implementation
18、,Typically,a number associated with each system callSystem-call interface maintains a table indexed according to these numbersThe system call interface invokes intended system call in OS kernel and returns status of the system call and any return valuesThe caller need know nothing about how the syst
19、em call is implementedJust needs to obey API and understand what OS will do as a result callMost details of OS interface hidden from programmer by API Managed by run-time support library(set of functions built into libraries included with compiler),API System Call OS Relationship,Standard C Library
20、Example,C program invoking printf()library call,which calls write()system call,System Call Parameter Passing,Often,more information is required than simply identity of desired system callExact type and amount of information vary according to OS and callThree general methods used to pass parameters t
21、o the OSSimplest:pass the parameters in registers In some cases,may be more parameters than registersParameters stored in a block,or table,in memory,and address of block passed as a parameter in a register This approach taken by Linux and SolarisParameters placed,or pushed,onto the stack by the prog
22、ram and popped off the stack by the operating system Block and stack methods do not limit the number or length of parameters being passed,Parameter Passing via Table,X:address of table,2.4 Types of System Calls,Process control end,abort/load,execute/create process,terminate process/get process attri
23、butes,set process attributes/wait for time/wait event,signal event/allocate and free memoryFile management create file,delete file/open,close/read,write,reposition/get file attributes,set file attributesDevice management request device,release device/read,write,reposition/get device attributes,set d
24、evice attributes/logically attach or detach devicesInformation maintenance get time or date,set time or date/get system data,set system data/get process,file,or device attributes/set process,file,or device attributesCommunications create,delete communication connection/send,receive messages/transfer
25、 status information/attach or detach remote devices,Examples of Windows and Unix System Calls,*Process control:MS-DOS execution,(a)At system startup(b)running a program,*FreeBSD Running Multiple Programs,2.5 System Programs,Provide a convenient environment for program development and executionSome o
26、f them are simply user interfaces to system calls;others are considerably more complexFile management-Create,delete,copy,rename,print,dump,list,and generally manipulate files and directoriesStatus informationSome ask the system for info-date,time,amount of available memory,disk space,number of users
27、Others provide detailed performance,logging,and debugging informationTypically,these programs format and print the output to the terminal or other output devicesSome systems implement a registry-used to store and retrieve configuration information,System Programs(contd),File modificationText editors
28、 to create and modify filesSpecial commands to search contents of files or perform transformations of the textProgramming-language support-Compilers,assemblers,debuggers and interpreters sometimes providedProgram loading and execution-Absolute loaders,relocatable loaders,linkage editors,and overlay-
29、loaders,debugging systems for higher-level and machine languageCommunications-Provide the mechanism for creating virtual connections among processes,users,and computer systemsAllow users to send messages to one anothers screens,browse web pages,send electronic-mail messages,log in remotely,transfer
30、files from one machine to another,2.6 Operating System Design and Implementation,Design and Implementation of OS not“solvable”,but some approaches have proven successfulInternal structure of different Operating Systems can vary widelyStart by defining goals and specifications Affected by choice of h
31、ardware,type of systemUser goals and System goalsUser goals operating system should be convenient to use,easy to learn,reliable,safe,and fastSystem goals operating system should be easy to design,implement,and maintain,as well as flexible,reliable,error-free,and efficient,Operating System Design and
32、 Implementation(Cont.),Important principle to separatePolicy:What will be done?Mechanism:How to do it?Mechanisms determine how to do something,policies decide what will be doneSuch as the timer construct is a Mechanism,and how long the timer is to be set is Policy.The separation of policy from mecha
33、nism is a very important principle,it allows maximum flexibility if policy decisions are to be changed laterImplementation Traditionally,operating systems have been written in assembly language.Now,however,they are most commonly written in higher-level languages such as C or C+.,2.7 Operating-System
34、 Structure,Simple Structure MS-DOS written to provide the most functionality in the least spaceNot divided into modulesAlthough MS-DOS has some structure,its interfaces and levels of functionality are not well separatedDifficult to implement and maintain.,Layered Approach,The operating system is div
35、ided into a number of layers(levels),each built on top of lower layers.The bottom layer(layer 0),is the hardware;the highest(layer N)is the user interface.With modularity,layers are selected such that each uses functions(operations)and services of only lower-level layersSimplicity of construction an
36、d debuggingIt is difficult to define the various layersLess efficient,UNIX,UNIX limited by hardware functionality,the original UNIX operating system had limited structuring.The UNIX OS consists of two separable partsSystems programsThe kernelConsists of everything below the system-call interface and
37、 above the physical hardwareProvides the file system,CPU scheduling,memory management,and other operating-system functions;a large number of functions for one level,UNIX System Structure,Microkernel System Structure,Moves as much nonessential parts from the kernel into“user”space,provide minimal pro
38、cess and memory management.Communication takes place between user modules using message passingBenefits:Easier to extend a microkernelEasier to port the operating system to new architecturesMore reliable(less code is running in kernel mode)More secureDetriments:Performance overhead of user space to
39、kernel space communicationExamples Mach True64 Unix QNX,Modules,Most modern operating systems implement module kernel Uses object-oriented approachEach core component is separateEach talks to the others over known interfacesEach is loadable as needed within the kernelAllows the kernel to provide cor
40、e services yet also allows certain features to be implemented dynamically.Overall,similar to layers but with more flexible,Solaris Modular Approach,Mac OS X hybrid structure,2.8 Virtual Machines,The fundamental idea behind a virtual machine is to abstract the hardware of a single computer into sever
41、al different execution environments,thereby creating the illusion that each separate execution environment is running its own private computer.A virtual machine takes the layered approach to its logical conclusion.It treats hardware and the operating system kernel as though they were all hardwareA v
42、irtual machine provides an interface identical to the underlying bare hardwareThe operating system creates the illusion of multiple processes,each executing on its own processor with its own(virtual)memory,Virtual Machines(Cont.),The resources of the physical computer are shared to create the virtua
43、l machinesCPU scheduling can create the appearance that users have their own processorSpooling and a file system can provide virtual card readers and virtual line printersA normal user time-sharing terminal serves as the virtual machine operators console,Virtual Machines(Cont.),(a)Nonvirtual machine
44、(b)virtual machine,Non-virtual Machine,Virtual Machine,Virtual Machines(Cont.),The virtual-machine concept provides complete protection of system resources since each virtual machine is isolated from all other virtual machines.This isolation,however,permits no direct sharing of resources.A virtual-m
45、achine system is a perfect vehicle for operating-systems research and development.System development is done on the virtual machine,instead of on a physical machine and so does not disrupt normal system operation.The virtual machine concept is difficult to implement due to the effort required to pro
46、vide an exact duplicate to the underlying machine,VMware Architecture,The Java Virtual Machine,2.9 Operating System Generation,Operating systems are designed to run on any of a class of machines;the system must be configured for each specific computer siteSYSGEN program obtains information concernin
47、g the specific configuration of the hardware systemBooting starting a computer by loading the kernelBootstrap program code stored in ROM that is able to locate the kernel,load it into memory,and start its execution,2.10 System Boot,Operating system must be made available to hardware so hardware can
48、start itSmall piece of code bootstrap loader,locates the kernel,loads it into memory,and starts itSometimes two-step process where boot block at fixed location loads bootstrap loaderWhen power initialized on system,execution starts at a fixed memory locationFirmware used to hold initial boot codeHomework 2.1 2 3 5 8 13,End of Chapter 2,
