Operating Systems : OverviewTopics for discussionGoals for the courseWhat is an Operating system?User InterfaceResource ManagerScheduling and resource managementMultiprogrammingProcessesProcessA simple implementation of processesDeadlockMemory managementProtection and SecuritySystem StructureSystem CallSome System Calls For Process Management and File ManagementOperating system Modular View01/13/19 B.Ramamurthy 1Operating Systems : OverviewBina RamamurthyCSE42101/13/19 B.Ramamurthy 2Topics for discussionWhat will you learn in this course? (goals)What is an Operating System (OS)?ProcessResourcesSystem callSummary01/13/19 B.Ramamurthy 3Goals for the courseStudy the working of an OS.Study the design and implementation of various components of an OS.Learn about the alternatives available to a designer at all levels of abstraction in an OS.Learn concurrent programming using processes, threads, and system calls.Understand the basics of distributed systems.Explore how you may contribute to solving many open problems in OS and distributed systems.01/13/19 B.Ramamurthy 4What is an Operating system?Interface managerHuman interaction made easyinterfacing, abstraction, control and sharingResource manager Efficient use of resourcesEnhances hardware features“virtual” time, space and resource (processes, threads) System and data security and protection provider01/13/19 B.Ramamurthy 5User InterfaceOperating system provides these facilities for the user:Program creation : editors, debuggers, other development tools.Program execution : load, files, IO operations.Access to IO devices: Read and writes.Controlled access to files: protection mechanisms, abstraction of underlying device.System access: Controls who can access the system.Error detection and response: external, internal, software or hardware error.Accounting: Collect stats., load sharing , for billing purposes.01/13/19 B.Ramamurthy 6Resource ManagerProcessors : Allocation of processes to processors, preemption, scheduling.Memory: Allocation of main memory.IO devices : when to access io devices, which ones etc.Files: Partitions, space allocation and maintenance.Applications, Data, objects.01/13/19 B.Ramamurthy 7Scheduling and resource managementScheduling and resource management combination is an Operations Research (OR) problem.Goals : Efficient use of resources, satisfy the service time requested by a process, say, in a real-time system and of course, fairness.Short-term and long-term scheduling.Queuing is one of the basic operations associated with scheduling. Interrupt is another important concept in the context of scheduling.01/13/19 B.Ramamurthy 8MultiprogrammingIf memory can hold several programs, then CPU can switch to another one whenever a program is awaiting for an I/O to completeThis is multitasking (multiprogramming)01/13/19 B.Ramamurthy 9ProcessesA program in execution, An entity that can be assigned to and executed on a processes,It is a unit of work.Multiprogramming, time-sharing and real-time transaction systems lead to the refinement of the concept of process.A process can be defined by its attributes and behaviors (An OO class definition?).When instances of this class co-exist we have concurrent processing.Issues in concurrent processing : synchronization, mutual exclusion, deadlock, communication.01/13/19 B.Ramamurthy 10ProcessIntroduced to obtain a systematic way of monitoring and controlling program executionA process is an executable program with: associated data (variables, buffers…) execution context: ie. all the information that the CPU needs to execute the process content of the processor registersthe OS needs to manage the process:priority of the processthe event (if any) after which the process is waitingProcess resources01/13/19 B.Ramamurthy 11A simple implementation of processesThe process index register contains the index into the process list of the currently executing process (B)A process switch from B to A consist of storing (in memory) B’s context and loading (in CPU registers) A’s context01/13/19 B.Ramamurthy 12Deadlock (a) A potential deadlock. (b) an actual deadlock.01/13/19 B.Ramamurthy 13Memory managementRequirements: Process isolation, automatic allocation and maintenance, protection and access control, long-term storage facilities.Virtual memory and file system facilities together satisfy all these requirements.Virtual memory allows programs to address the memory from a logical point of view without regard to the amount of main memory available.File : persistent storage for programs and data. Can view file also as an class? File concept makes makes access control and protection convenient for the OS.01/13/19 B.Ramamurthy 14Protection and SecurityWhen sharing resources, protection of the systems and user resources from intentional as well as inadvertent misuse. Protection generally deals with access control. Ex: Read only fileSecurity deals usually with threats from outside the system that affects the integrity and availability of the system and information with the system.Example: username, password to access system. Data encryption to protect information.01/13/19 B.Ramamurthy 15System StructureBecause of it’s enormous complexity, we view the OS system as a series of levelsEach level performs a related subset of functionsEach level relies on the next lower level to perform more primitive functionsWell defined interfaces: one level can be modified without affecting other levelsThis decomposes a problem into a number of more manageable sub problems01/13/19 B.Ramamurthy 16System Call There are 11 steps in making the system call read (fd, buffer, nbytes)01/13/19 B.Ramamurthy 17Some System Calls For Process Management and File Management01/13/19 B.Ramamurthy 18Operating system Modular ViewHardware +interruptsVirtual MemProcess + primitivesComm. PrmtvsFile sys.DevicesDirectoriesShellUser ProcessesWeb ClientsApplication ClientsWeb
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