Operating System OverviewChapter 2

Operating SystemA program that controls the execution of application programsAn interface between applications and hardware

Operating System ObjectivesConvenienceMakes the computer more convenient to useEfficiencyAllows computer system resources to be used in an efficient mannerAbility to evolvePermit effective development, testing, and introduction of new system functions without interfering with service

Layers of Computer System

Services Provided by the Operating SystemProgram developmentEditors and debuggersProgram executionAccess to I/O devicesControlled access to filesSystem access

Services Provided by the Operating SystemError detection and responseInternal and external hardware errorsMemory errorDevice failureSoftware errorsArithmetic overflowAccess forbidden memory locationsOperating system cannot grant request of application

Services Provided by the Operating SystemAccountingCollect usage statisticsMonitor performanceUsed to anticipate future enhancementsUsed for billing purposes

Operating SystemResponsible for managing resourcesFunctions same way as ordinary computer softwareIt is program that is executedOperating system relinquishes control of the processor

KernelPortion of operating system that is in main memoryContains most frequently used functionsAlso called the nucleus

Evolution of an Operating SystemHardware upgrades plus new types of hardwareNew servicesFixes

Evolution of Operating SystemsSerial ProcessingNo operating systemMachines run from a console with display lights, toggle switches, input device, and printerSchedule timeSetup included loading the compiler, source program, saving compiled program, and loading and linking

Evolution of Operating SystemsSimple Batch SystemsMonitorsSoftware that controls the sequence of eventsBatch jobs togetherProgram branches back to monitor when finished

Job Control Language (JCL)Special type of programming languageProvides instruction to the monitorWhat compiler to useWhat data to use

Hardware FeaturesMemory protectionDo not allow the memory area containing the monitor to be alteredTimerPrevents a job from monopolizing the system

Hardware FeaturesPrivileged instructionsCertain machine level instructions can only be executed by the monitorInterruptsEarly computer models did not have this capability

Memory ProtectionUser program executes in user modeCertain instructions may not be executedMonitor executes in system modeKernel modePrivileged instructions are executedProtected areas of memory may be accessed

I/O Devices Slow

UniprogrammingProcessor must wait for I/O instruction to complete before preceding

MultiprogrammingWhen one job needs to wait for I/O, the processor can switch to the other job

Multiprogramming

Utilization Histograms

Example

Time SharingUsing multiprogramming to handle multiple interactive jobsProcessors time is shared among multiple usersMultiple users simultaneously access the system through terminals

Compatible Time-Sharing System (CTSS)First time-sharing system developed at MIT

Major AchievementsProcessesMemory ManagementInformation protection and securityScheduling and resource managementSystem structure

ProcessesA program in executionAn instance of a program running on a computerThe entity that can be assigned to and executed on a processorA unit of activity characterized by a single sequential thread of execution, a current state, and an associated set of system resources

Difficulties with Designing System SoftwareImproper synchronizationEnsure a process waiting for an I/O device receives the signalFailed mutual exclusionNondeterminate program operationProgram should only depend on input to it, not on the activities of other programsDeadlocks

ProcessConsists of three componentsAn executable programAssociated data needed by the programExecution context of the programAll information the operating system needs to manage the process

Process

Memory ManagementProcess isolationAutomatic allocation and managementSupport of modular programmingProtection and access controlLong-term storage

Virtual MemoryAllows programmers to address memory from a logical point of viewNo hiatus between the execution of successive processes while one process was written out to secondary store and the successor proceess was read in

Virtual Memory and File SystemImplements long-term storeInformation stored in named objects called files

PagingAllows process to be comprised of a number of fixed-size blocks, called pagesVirtual address is a page number and an offset within the pageEach page may be located any where in main memoryReal address or physical address in main memory

Virtual Memory

Virtual Memory Addressing

Information Protection and SecurityAvailabilityConcerned with protecting the system against interruptionConfidentialityAssuring that users cannot read data for which access is unauthorized

Information Protection and SecurityData integrityProtection of data from unauthorized modificationAuthenticityConcerned with the proper verification of the identity of users and the validity of messages or data

Scheduling and Resource ManagementFairnessGive equal and fair access to resourcesDifferential responsivenessDiscriminate among different classes of jobsEfficiencyMaximize throughput, minimize response time, and accommodate as many uses as possible

Key Elements ofOperating System

System StructureView the system as a series of levelsEach level performs a related subset of functionsEach level relies on the next lower level to perform more primitive functionsThis decomposes a problem into a number of more manageable subproblems

Process Hardware LevelsLevel 1Electronic circuitsObjects are registers, memory cells, and logic gatesOperations are clearing a register or reading a memory locationLevel 2Processors instruction setOperations such as add, subtract, load, and store

Process Hardware LevelsLevel 3Adds the concept of a procedure or subroutine, plus call/return operationsLevel 4Interrupts

Concepts with MultiprogrammingLevel 5Process as a program in executionSuspend and resume processesLevel 6Secondary storage devicesTransfer of blocks of dataLevel 7Creates logical address space for processesOrganizes virtual address space into blocks

Deal with External ObjectsLevel 8Communication of information and messages between processesLevel 9Supports long-term storage of named filesLevel 10Provides access to external devices using standardized interfaces

Deal with External ObjectsLevel 11Responsible for maintaining the association between the external and internal identifiersLevel 12Provides full-featured facility for the support of processesLevel 13Provides an interface to the operating system for the user

Modern Operating SystemsMicrokernel architectureAssigns only a few essential functions to the kernelAddress spacesInterprocess communication (IPC)Basic scheduling

Modern Operating SystemsMultithreadingProcess is divided into threads that can run concurrentlyThreadDispatchable unit of workexecutes sequentially and is interruptableProcess is a collection of one or more threads

Modern Operating SystemsSymmetric multiprocessing (SMP)There are multiple processorsThese processors share same main memory and I/O facilitiesAll processors can perform the same functions

Multiprogramming and Multiprocessing

Modern Operating SystemsDistributed operating systemsProvides the illusion of a single main memory space and single secondary memory space

Modern Operating SystemsObject-oriented designUsed for adding modular extensions to a small kernelEnables programmers to customize an operating system without disrupting system integrity

Windows ArchitectureModular structure for flexibilityExecutes on a variety of hardware platformsSupports application written for other operating system

Operating System OrganizationModified microkernel architectureNot a pure microkernel Many system functions outside of the microkernel run in kernel modeAny module can be removed, upgraded, or replaced without rewriting the entire system

Kernel-Mode ComponentsExecutiveContains base operating system servicesMemory managementProcess and thread managementSecurityI/OInterprocess communicationKernelConsists of the most used components

Kernel-Mode ComponentsHardware abstraction layer (HAL)Isolates the operating system from platform-specific hardware differencesDevice driversTranslate user I/O function calls into specific hardware device I/O requestsWindowing and graphics systemsImplements the graphical user interface (GUI)

Windows ExecutiveI/O managerCache managerObject managerPlug and play managerPower managerSecurity reference monitorVirtual memory managerProcess/thread managerConfiguration managerLocal procedure call (LPC) facility

User-Mode ProcessesSpecial system support processesEx: logon process and the session managerService processesEnvironment subsystemsUser applications

Client/Server ModelSimplifies the ExecutivePossible to construct a variety of APIsImproves reliabilityEach service runs on a separate process with its own partition of memoryClients cannot not directly access hardwareProvides a uniform means for applications to communicate via LPCProvides base for distributed computing

Threads and SMPOperating system routines can run on any available processorDifferent routines can execute simultaneously on different processorsMultiple threads of execution within a single process may execute on different processors simultaneouslyServer processes may use multiple threadsShare data and resources between process

Windows ObjectsEncapsulationObject consists of one or more data items and one or more proceduresObject class or instanceCreate specified instances of an objectInheritanceSupport to some extent in the ExecutivePolymorphism

UNIXHardware is surrounded by the operating system softwareOperating system is called the system kernelComes with a number of user services and interfacesShellComponents of the C compiler

UNIX

UNIX Kernel

Modern UNIX Kernel

Modern UNIX SystemsSystem V Release 4 (SVR4)Solaris 94.4BSDLinux