Operating Systems : OverviewTopics for discussionGoals for the courseWhat is an Operating system?User InterfaceResource ManagerMultiprogrammingMultiprogrammed Batch SystemsProcessesProcessA simple implementation of processesMemory managementProtection and SecurityScheduling and resource managementScheduling and Resource ManagementFile SystemSystem StructureStructure of OSCharacteristics of Modern Operating SystemsMicrokernel architectureMultithreadingSymmetric Multiprocessing (SMP)Operating system Modular ViewTypes of OS01/13/19 B.R amamurthy 1Operating Systems : OverviewBina RamamurthyCSE42101/13/19 B.R amamurthy 2Topics for discussionWhat will you learn in this course? (goals)What is an Operating System (OS)?Evolution of OS Important OS ComponentsMajor achievementsOperating system design hierarchySample systems01/13/19 B.R amamurthy 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.R amamurthy 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.R amamurthy 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.R amamurthy 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.R amamurthy 7MultiprogrammingFrom uniprogramming to multiprogramming systems:See Fig.2.5Multiprogramming systems: batch programs, objective : maximize system (processor) utilization.Time sharing systems: Objective is minimize response time. Typical programs are interactive.01/13/19 B.R amamurthy 8Multiprogrammed Batch SystemsIf 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.R amamurthy 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 : it can be viewed as an Abstract Data Type (ADT). When instances of this ADT co-exist we have concurrent processing.Issues in concurrent processing : synchronization, mutual exclusion, deadlock, communication.01/13/19 B.R amamurthy 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 process•the event (if any) after which the process is waiting•other data (that we will introduce later)01/13/19 B.R amamurthy 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 contextA data structure that provides flexibility (to add new features)01/13/19 B.R amamurthy 12Memory 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 ADT? File concept makes makes access control and protection convenient for the OS.01/13/19 B.R amamurthy 13Protection 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.R amamurthy 14Scheduling and resource managementScheduling and resource management 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.R amamurthy 15Scheduling and Resource ManagementDifferential responsivenessdiscriminate between different classes of jobsFairnessgive equal and fair access to all processes of the same classEfficiencymaximize throughput, minimize response time, and accommodate as many users as possible01/13/19 B.R amamurthy 16File SystemImplements long-term store (often on disk)Information stored in named objects called filesa convenient unit of access and protection for OSFiles (and portions) may be copied into virtual memory for manipulation by programs01/13/19 B.R
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