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1/25/02 CSE421, Spring 2002 1Introduction to Operating SystemsB. Ramamurthy(adapted from C. Egert’s and W. Stallings’ slides)1/25/02 CSE421, Spring 2002 2IntroductionA computer system consists ofn hardwaren system programsn application programsAn Operating System?What is an Operating System?n A program that acts as an intermediary between a user of a computer and the computer hardware.What is the purpose of an operating system?n To provide an environment in which a user can execute programs.What are the goals of an Operating System?n The primary goal of an Operating System is to make the computer system convenient to use.n The secondary goal is to make the computer system efficient to use.Computer System ComponentsHardware – provides basic computing resources (CPU, memory, I/O devices).Operating system – controls and coordinates the use of the hardware among the various application programs for the various users.Applications programs – define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs).Users (people, machines, other computers).1/25/02 CSE421, Spring 2002 6Computer Hardware Review (1)Components of a simple personal computerMonitorBus1/25/02 CSE421, Spring 2002 7Computer Hardware Review (2)(a) A three-stage pipeline(b) A superscalar CPU1/25/02 CSE421, Spring 2002 8Computer Hardware Review (3)Typical memory hierarchyn numbers shown are rough approximationsFunction of Operating SystemOS as Extended machinen Computer Architecture shows that computer is made up of chips and wiresn We do not want to program on the bare metaln Virtual machine creates a hardware abstractionn Abstract machine can provide hardware independent interfacesn Increase portabilityn Allow greater protectionn Implication is that it is much faster and easier to program with less errorsFunction of Operating SystemOS as resource managern Coordination and control of limited resources such as memory, disk, network, etcn Deal with resource conflictsn Deal with resource fairnessn Make access efficient as possibleParts of an Operating SystemNo universal agreement on the topic, but most likelyn Memory Managementn IO Managementn CPU Schedulingn IPCn MultiTasking/Multiprogramming(On some Operating System, this functionality is provided by a single program known as the kernel)What about?n File Systemn Multimedia Supportn UI (X Windows, MSWin)n Internet Browser?n Why would extras be importantMultiprogrammingMemory partitioned into several piecesCPU Starts a jobIf the job is waiting for IO, the CPU can switch to another taskMultitasking (Time-sharing)Extension of Multiprogrammingn Need for user interactivityn Instead of switching jobs when waiting for IO, a timer causes jobs to switchUser interacts with computer via CRT and keyboardn Systems have to balance CPU utilization against response timen Better device managementNeed for file system to allow user to access data and codeNeed to provide user with an “interaction environment”Virtual MemoryPrograms can be larger than memoryn Program loaded into memory as neededn Active program and data “swapped” to a disk until neededMemory space treated uniformly1/25/02 CSE421, Spring 2002 15Operating System Concepts (1): Process ManagementA process treen A created two child processes, B and Cn B created three child processes, D, E, and F1/25/02 CSE421, Spring 2002 16Operating System Concepts (2): Deadlock Handling(a) A potential deadlock. (b) an actual deadlock.1/25/02 CSE421, Spring 2002 17Operating System Concepts (3): File SystemFile system for a university department1/25/02 CSE421, Spring 2002 18Operating System Concepts (5): Inter-process CommunicationTwo processes connected by a pipe1/25/02 CSE421, Spring 2002 19Steps in Making a System Call There are 11 steps in making the system callread (fd, buffer, nbytes)1/25/02 CSE421, Spring 2002 20Some System Calls For Process Management and File Management1/25/02 CSE421, Spring 2002 21Metric UnitsThe metric prefixesParallel Systems Symmetric multiprocessing (SMP)n Each processor runs an identical copy of the operating system.n Many processes can run at once without performance deterioration.n Most modern operating systems support SMPAsymmetric multiprocessingn Each processor is assigned a specific task; master processor schedules and allocates work to slave processors.n More common in extremely large systemsReal-Time SystemsOften used as a control device in a dedicated application such as controlling scientific experiments, medical imaging systems, industrial control systems, and some display systems.Well-defined fixed-time constraints (known as deterministic).Hard real-time system.n Secondary storage limited or absent, data stored in short-term memory, or read-only memory (ROM)n Conflicts with time-sharing systems, not supported by general-purpose operating systems.Soft real-time systemn Limited utility in industrial control or roboticsn Useful in applications (multimedia, virtual reality) requiring advanced operating-system features.Distributed SystemsDistribute the computation among several physical processors.Loosely coupled system– each processor has its own local memory; processors communicate with one another through various communications lines, such as high-speed buses or telephone lines.Advantages of distributed systems.n Resources Sharing n Computation speed up – load sharing n Reliabilityn


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UB CSE 421 - Study Notes

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