Operating system lecture notes

Operating system lecture notes in Operating System uploaded at P.R.Engineering college

Operating system lecture notes in Operating System at P.R.Engineering college uploaded by P.R.Engineering college Staff in lecturenotes.net

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Chapter 1:   Introduction

 What is an Operating System?
 Mainframe Systems
 Desktop Systems
 Multiprocessor Systems
 Distributed Systems 
 Clustered System
 Real -Time Systems
 Handheld Systems
 Computing Environments

What is an Operating System?

 A program that acts as an intermediary between a user of a computer and the computer hardware.
 Operating system goals:
 Execute user programs and make solving user problems easier.
 Make the computer system convenient to use.
 Use the computer hardware in an efficient manner.

Computer System Components

1. Hardware – provides basic computing resources (CPU, memory, I/O devices).
2. Operating system – controls and coordinates the use of the hardware among the various application programs for the various users.
3. 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).
4. Users (people, machines, other computers).

Abstract View of System Components

Operating System Definitions
 Resource allocator – manages and allocates resources.
 Control program – controls the execution of user programs and operations of I/O devices .
 Kernel – the one program running at all times (all else being application programs).

Mainframe Systems
 Reduce setup time by batching similar jobs
 Automatic job sequencing – automatically transfers control from one job to another.  First rudimentary operating system.
 Resident monitor
 initial control in monitor 
 control transfers to job 
 when job completes control transfers pack to monitor

Memory Layout for a Simple Batch System

Multiprogrammed Batch Systems

OS Features Needed for Multiprogramming

 I/O routine supplied by the system.
 Memory management – the system must allocate the memory to several jobs.
 CPU scheduling – the system must choose among several jobs ready to run.
 Allocation of devices.

Time-Sharing Systems–Interactive Computing 
 The CPU is multiplexed among several jobs that are kept in memory and on disk (the CPU is allocated to a job only if the job is in memory).
 A job swapped in and out of memory to the disk.
 On-line communication between the user and the system is provided; when the operating system finishes the execution of one command, it seeks the next “control statement” from the user’s keyboard.
 On-line system must be available for users to access data and code.
Desktop Systems
 Personal computers – computer system dedicated to a single user.
 I/O devices – keyboards, mice, display screens, small printers.
 User convenience and responsiveness.
 Can adopt technology developed for larger operating system’ often individuals have sole use of computer and do not need advanced CPU utilization of protection features.
 May run several different types of operating systems (Windows, MacOS, UNIX, Linux)
Parallel Systems
 Multiprocessor systems with more than on CPU in close communication.
 Tightly coupled system – processors share memory and a clock; communication usually takes place through the shared memory.
 Advantages of parallel system: 
 Increased throughput
 Economical 
 Increased reliability
 graceful degradation
 fail-soft systems
 Symmetric multiprocessing (SMP)
 Each processor runs and identical copy of the operating system.
 Many processes can run at once without performance deterioration.
 Most modern operating systems support SMP
 Asymmetric multiprocessing
 Each processor is assigned a specific task; master processor schedules and allocated work to slave processors.
 More common in extremely large systems

Symmetric Multiprocessing Architecture

Distributed Systems
 Distribute 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.
 Resources Sharing 
 Computation speed up – load sharing 
 Reliability
 Communications
 Requires networking infrastructure.
 Local area networks (LAN) or Wide area networks (WAN)
 May be either client-server or peer-to-peer systems.
General Structure of Client-Server

Clustered Systems

 Clustering allows two or more systems to share storage.
 Provides high reliability.
 Asymmetric clustering: one server runs the application while other servers standby.
 Symmetric clustering: all N hosts are running the application.
Real-Time Systems
 Often 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.
 Real-Time systems may be either hard or soft real-time.
 Hard real-time:
 Secondary storage limited or absent, data stored in short term memory, or read-only memory (ROM)
 Conflicts with time-sharing systems, not supported by general-purpose operating systems.
 Soft real-time
 Limited utility in industrial control of robotics
 Useful in applications (multimedia, virtual reality) requiring advanced operating-system features.
Handheld Systems
 Personal Digital Assistants (PDAs)
 Cellular telephones
 Issues:
 Limited memory
 Slow processors & Small display screens.
Migration of Operating-System Concepts and Features
 
Computing Environments
 Traditional computing
 Web-Based Computing
 Embedded Computing

Chapter 2:  Computer-System Structures
 Computer System Operation
 I/O Structure 
 Storage Structure
 Storage Hierarchy
 Hardware Protection
 General System Architecture
Computer-System Architecture
 
Computer-System Operation
 I/O devices and the CPU can execute concurrently.
 Each device controller is in charge of a particular device type.
 Each device controller has a local buffer.
 CPU moves data from/to main memory to/from local buffers
 I/O is from the device to local buffer of controller.
 Device controller informs CPU that it has finished its operation by causing an interrupt.
Common Functions of Interrupts
 Interrupt transfers control to the interrupt service routine generally, through the interrupt vector, which contains the addresses of all the service routines.
 Interrupt architecture must save the address of the interrupted instruction.
 Incoming interrupts are disabled while another interrupt is being processed to prevent a lost interrupt.
 A trap is a software-generated interrupt caused either by an error or a user request.
 An operating system is interrupt driven.

Interrupt Handling

 The operating system preserves the state of the CPU by storing registers and the program counter.
 Determines which type of interrupt has occurred:
 polling
 vectored interrupt system
 Separate segments of code determine what action should be taken for each type of interrupt

Interrupt Time Line For a Single Process Doing Output

I/O Structure

 After I/O starts, control returns to user program only upon I/O completion.
 Wait instruction idles the CPU until the next interrupt
 Wait loop (contention for memory access).
 At most one I/O request is outstanding at a time, no simultaneous I/O processing.
 After I/O starts, control returns to user program without waiting for I/O completion.
 System call – request to the operating system to allow user to wait for I/O completion.
 Device-status table contains entry for each I/O device indicating its type, address, and state.
 Operating system indexes into I/O device table to determine device status and to modify table entry to include interrupt.

Two I/O Methods

Device-Status Table

Direct Memory Access Structure
 Used for high-speed I/O devices able to transmit information at close to memory speeds.
 Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention.
 Only on interrupt is generated per block, rather than the one interrupt per byte.

Storage Structure
 Main memory – only large storage media that the CPU can access directly.
 Secondary storage – extension of main memory that provides large nonvolatile storage capacity.
 Magnetic disks – rigid metal or glass platters covered with magnetic recording material 
 Disk surface is logically divided into tracks, which are subdivided into sectors.
 The disk controller determines the logical interaction between the device and the computer.

Moving-Head Disk Mechanism

Title:
Operating system lecture notes

Subject:
Operating System

Institute:
P.R.Engineering college

Operating system lecture notes

Operating system lecture notes in Operating System uploaded at P.R.Engineering college

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