OS-Unit I -part 1-Thomas sir

8/3/2019 OS-Unit I -part 1-Thomas sir

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Unit I: Fundamentals (part1)Unit I: Fundamentals (part1)


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1.2 Silberschatz, Galvin and Gagne 2005Operating System Principles

Contents..Contents..

s

What Operating Systems Dos Computer-System Organization

s Computer-System Architecture

s Operating-System Structure

s Operating-System Operations

s Process Management

s Memory Management

s Storage Management

s Operating System Services


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ObjectivesObjectives

s

To provide a grand tour of the major operating systemscomponents

s To provide coverage of basic computer system organization


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What is an Operating System?What is an Operating System?

s A program that acts as an intermediary between a user of acomputer and the computer hardware.

s Operating system goals:

q Execute user programs and make solving user problemseasier.

q Make the computer system convenient to use.

s Use the computer hardware in an efficient manner.


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Four Components of a Computer SystemFour Components of a Computer System


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Operating System DefinitionOperating System Definition

s OS is a resource allocatorq Manages all resources

q Decides between conflicting requests for efficient and fairresource use

s OS is a control program

q Controls execution of programs to prevent errors and improperuse of the computer



Operating System Definition (Cont.)Operating System Definition (Cont.)

s No universally accepted definition

s Everything a vendor ships when you order an operating systemis good approximation

q But varies wildly

s The one program running at all times on the computer is thekernel. Everything else is either a system program (ships withthe operating system) or an application program



Operating System GenerationOperating System Generation

s Operating systems are designed to run on any of a class ofmachines; the system must be configured for each specificcomputer site

s Booting starting a computer by loading the kernel

s Bootstrap program code stored in ROM that is able to locate thekernel, load it into memory, and start its execution



System BootSystem Boot

s Operating system must be made available to hardware so hardware can start

it

q Small piece of code bootstrap loader, locates the kernel, loads it intomemory, and starts it.

s bootstrap program is loaded at power-up or reboot

q Typically stored in ROM or EEPROM, generally known as firmware

q Initializates all aspects of system

q Loads operating system kernel and starts execution

s Sometimes two-step process where boot block at fixed location loadsbootstrap loader

s When power initialized on system, execution starts at a fixed memory location

q

Firmware used to hold initial boot code



Computer System OrganizationComputer System Organization

s Computer-system operation

q One or more CPUs, device controllers connect throughcommon bus providing access to shared memory

q Concurrent execution of CPUs and devices competing formemory cycles



Computer-System OperationComputer-System Operation

s I/O devices and the CPU can execute concurrently.

s Each device controller is in charge of a particular device type.

s Each device controller has a local buffer.

s CPU moves data from/to main memory to/from local buffers

s I/O is from the device to local buffer of controller.

s Device controller informs CPU that it has finished its operation bycausing an interrupt.



Common Functions of InterruptsCommon Functions of Interrupts

s Interrupt transfers control to the interrupt service routine generally,through the interrupt vector, which contains the addresses of all theservice routines.

s Interrupt architecture must save the address of the interruptedinstruction.

s Incoming interrupts are disabledwhile another interrupt is beingprocessed to prevent a lost interrupt.

s A trapis a software-generated interrupt caused either by an error ora user request.

s An operating system is interruptdriven.



Storage StructureStorage Structure

s Main memory only large storage media that the CPU can accessdirectly.

s Secondary storage extension of main memory that provides largenonvolatile storage capacity.

s Magnetic disks rigid metal or glass platters covered with magneticrecording material

q Disk surface is logically divided into tracks, which aresubdivided into sectors.

q The disk controllerdetermines the logical interaction betweenthe device and the computer.



Storage HierarchyStorage Hierarchy

s Storage systems organized in hierarchy.

q Speed

q Cost

q Volatility

s Caching copying information into faster storage system; main

memory can be viewed as a last cachefor secondary storage.



Storage-Device HierarchyStorage-Device Hierarchy



CachingCaching

s Important principle, performed at many levels in a computer (inhardware, operating system, software)

s Information in use copied from slower to faster storage temporarily

s Faster storage (cache) checked first to determine if information isthere

q

If it is, information used directly from the cache (fast)q If not, data copied to cache and used there

s Cache smaller than storage being cached

q Cache management important design problem

q Cache size and replacement policy



Performance of Various Levels of StoragePerformance of Various Levels of Storage

s Movement between levels of storage hierarchy can be explicit orimplicit



Migration of Integer A from Disk to RegisterMigration of Integer A from Disk to Register

s Multitasking environments must be careful to use most recentvalue, not matter where it is stored in the storage hierarchy

s Multiprocessor environment must provide cache coherency inhardware such that all CPUs have the most recent value in theircache.



Cache and Main MemoryCache and Main Memory



Operating System StructureOperating System Structure

s Multiprogramming needed for efficiency

q Single user cannot keep CPU and I/O devices busy at all times

q Multiprogramming organizes jobs (code and data) so CPU always has oneto execute

q A subset of total jobs in system is kept in memory

q One job selected and run via job scheduling

q When it has to wait (for I/O for example), OS switches to another jobs Timesharing (multitasking) is logical extension in which CPU switches jobs

so frequently that users can interact with each job while it is running, creatinginteractive computing

q Response time should be < 1 second

q Each user has at least one program executing in memory process

q If several jobs ready to run at the same time CPU schedulingq If processes dont fit in memory, swapping moves them in and out to run

q Virtual memory allows execution of processes not completely in memory



Memory Layout for Multiprogrammed SystemMemory Layout for Multiprogrammed System


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Transition from User to Kernel ModeTransition from User to Kernel Mode

s Timer to prevent infinite loop / process hogging resources

q Set interrupt after specific period

q Operating system decrements counter

q When counter zero generate an interrupt

q Set up before scheduling process to regain control or terminate

program that exceeds allotted time


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Process ManagementProcess Management

s

A process is a program in execution. It is a unit of work within the system.Program is a passive entity, process is an active entity.

s Process needs resources to accomplish its task

q CPU, memory, I/O, files

q Initialization data

s Process termination requires reclaim of any reusable resources

s Single-threaded process has one program counter specifying location ofnext instruction to execute

q Process executes instructions sequentially, one at a time, untilcompletion

s Multi-threaded process has one program counter per thread

s Typically system has many processes, some user, some operating system

running concurrently on one or more CPUsq Concurrency by multiplexing the CPUs among the processes / threads


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Process Management ActivitiesProcess Management Activities

The operating system is responsible for the following activities inconnection with process management:

s Creating and deleting both user and system processes

s Suspending and resuming processes

s Providing mechanisms for process synchronization

s Providing mechanisms for process communications Providing mechanisms for deadlock handling


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Memory ManagementMemory Management

s All data in memory before and after processing

s All instructions in memory in order to execute

s Memory management determines what is in memory when

q Optimizing CPU utilization and computer response to users

s Memory management activities

q Keeping track of which parts of memory are currently beingused and by whom

q Deciding which processes (or parts thereof) and data to moveinto and out of memory

q Allocating and deallocating memory space as needed


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Storage ManagementStorage Management

sOS provides uniform, logical view of information storageq Abstracts physical properties to logical storage unit - file

q Each medium is controlled by device (i.e., disk drive, tape drive)

Varying properties include access speed, capacity, data-transfer rate, access method (sequential or random)

sFile-System managementq Files usually organized into directories

q Access control on most systems to determine who can accesswhat

q OS activities include

Creating and deleting files and directories Primitives to manipulate files and dirs

Mapping files onto secondary storage

Backup files onto stable (non-volatile) storage media


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Mass-Storage ManagementMass-Storage Management

s Usually disks used to store data that does not fit in main memory or data

that must be kept for a long period of time.

s Proper management is of central importance

s Entire speed of computer operation hinges on disk subsystem and itsalgorithms

s OS activities

q Free-space managementq Storage allocation

q Disk scheduling

s Some storage need not be fast

q Tertiary storage includes optical storage, magnetic tape

q Still must be managed

q Varies between WORM (write-once, read-many-times) and RW (read-write)


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OS-Unit I -part 1-Thomas sir

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