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Net 321 : Computer Operating System. Lecture # 1 : Introduction. Chapter 1: Introduction. Chapter 1: Introduction. What Operating Systems Do Computer-System Organization Computer-System Architecture Operating-System Structure Operating-System Operations Kernel Data Structures

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Net 321 computer operating system

Net 321 :Computer Operating System

Lecture # 1 : Introduction

Networks and Communication Department

Chapter 1 introduction1
Chapter 1: Introduction

What Operating Systems Do

Computer-System Organization

Computer-System Architecture

Operating-System Structure

Operating-System Operations

Kernel Data Structures

Computing Environments


To describe the basic organization of computer systems

To provide a grand tour of the major components of operating systems

To give an overview of the many types of computing environments

Intro what is an operating system
Intro: 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 structure
Computer System Structure

Computer system can be divided into four components:

Hardware – provides basic computing resources

CPU, memory, I/O devices

Operating system

Controls and coordinates use of hardware among various applications and users

Application programs – define the ways in which the system resources are used to solve the computing problems of the users

Word processors, compilers, web browsers, database systems, video games


People, machines, other computers

The operating system s role
The operating system’s Role

Depends on the point of view

  • User View:

    • Single User (personal computer)

      • OS designed for ease of use , with some attention paid to performance and no paid for resource utilization.

    • Multiple User’s (mainframe or minicomputer)

      • OS designed to maximize resource utilization.

    • Workstations users connected to networks of other workstations and servers

      • OS designed to compromise between individual usability and resource utilization.

The operating system s role cont
The operating system’s Role (cont.)

  • System View:

    • OS is a resource allocator

      • Manages all resources

      • Decides between conflicting requests for efficient and fair resource use

      • It is important when many users access the same mainframe or minicomputer

    • OS is a control program

      • Controls execution of programs to prevent errors and improper use of the computer

      • It is especially concerned with the operation and control of I/O devices.

Operating system definition
Operating System Definition

No universally accepted definition

“The one program running at all times on the computer” is the kernel.

Everything else is either

a system program : whichassociated with the operating system but are not part of the kernel

an application program: which include all programs not associated with the operating system

An operating system is a software that manages

the computer hardware, as well as providing an

environment for application programs to run.

Computer startup
Computer Startup

bootstrap programis loaded at power-up or reboot

Typically stored in ROM or EPROM, generally known as firmware

Initializes all aspects of system

Loads operating system kernel and starts execution

Computer system organization
Computer-System Organization

  • Computer-System Operation

  • Storage Structure

  • I/O Structure

Computer system organization1
Computer System Organization

Computer-system operation

One or more CPUs, device controllers connect through common bus providing access to shared memory

Concurrent execution of CPUs and devices competing for memory cycles

Computer system operation cont
Computer System Operation (cont.)


  • The occurrence of an event is usually signaled by an interrupt from either the hardware or the software.

    • Hardware interrupts by sending a signal to the CPU through system bus.

    • Software interrupts by executing a special operation called a system call.

The interrupt is signal that gets the attention of the CPU and is usually

generated when I/O is required.

For example,

hardware interrupts are generated when a key is pressed or when the

mouse is moved.

Software interrupts are generated by a program requiring disk input or


Computer system operation
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

Storage structure
Storage Structure

Main memory – only large storage media that the CPU can access directly


Typically volatile

Secondary storage – extension of main memory that provides large nonvolatilestorage capacity

Storage hierarchy
Storage Hierarchy

Storage systems organized in hierarchy




Caching – copying information into faster storage system; main memory can be viewed as a cache for secondary storage

I o structure
I/O Structure

  • each device controller is in charge of a specific type of device.

  • A device controller maintains some local buffer storage and a set of special-purpose registers.

  • OS have a device driver for each device controller. This device driver understands the device controller and presents a uniform interface to device to the rest of the operating system.

I o structure cont
I/O Structure(cont.)

  • To start interrupt-driven I/O operation,

    • The device driver loads the appropriate registers within the device controller.

    • The device controller examines the contents of registers to determine what action to take.

    • The controller starts the transfer of data from the device to its local buffer.

    • Once the transfer of data is complete, the device controller informs the device driver via an interrupt that it has finished its operation.

    • The device driver returns control to the OS.

      What is the problem of this form?

I o structure cont1
I/O Structure (cont.)

  • Direct Memory Access (DMA)

    • 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 one interrupt is generated per block, rather than the one interrupt per byte

How a modern computer works
How a Modern Computer Works

A von Neumann architecture

Computer system architecture
Computer-System Architecture

  • Most systems use a single general-purpose processor (PDAs through mainframes)

    • Most systems have special-purpose processors as well

  • Multiprocessors systems growing in use and importance

    • Also known as parallel systems, tightly-coupled systems

    • Advantages include

      • Increased throughput

      • Economy of scale

      • Increased reliability – fault tolerance

    • Two types

      • Asymmetric Multiprocessing (master-slave relationship)

      • Symmetric Multiprocessing (all processors are peers)

A dual core design
A Dual-Core Design

  • Processors were originally developed with only one core.

  • The core is the part of the processor that actually performs the reading

    and executing of the instruction. Single-core processors can only

    process one instruction at a time

  • Dual-core processor contains two cores (Such as Intel Core Duo).

Operating system structure
Operating System Structure

  • Multiprogramming needed for efficiency

    • Multiprogramming organizes jobs (code and data) so CPU always has one to execute. (Increase CPU Utilization.)

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

    • One job selected and run via job scheduling

    • When it has to wait (for I/O for example), OS switches to another job

Multiprogramming systems provide an environment in

which the various system resources are utilized effectively,

Not for user interaction with the computer system


  • Processor must wait for I/O instruction to complete before preceding


  • When one job needs to wait for I/O, the processor can switch to the other job

Operating system structure cont
Operating System Structure (cont.)

  • Timesharing (multitasking) is logical extension of multiprogramming in which CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing

    • Response time should be < 1 second

    • Each user has at least one program executing in memory process

    • If several jobs ready to run at the same time  CPU scheduling

    • If processes don’t fit in memory, swapping moves them in and out to run

    • Virtual memory allows execution of processes not completely in memory

Time sharing
Time Sharing

  • Using multiprogramming to handle multiple interactive jobs

  • Processor’s time is shared among multiple users

  • Multiple users simultaneously access the system through terminals

Operating system operations
Operating-System Operations

  • OS are interrupt driven.

  • Since the OS and the user share the HW and SW resources , we must sure that an error in user program could cause problems only for its running.

    • EX: process problems include infinite loop, this loop could prevent the correct operation of many other processors or the OS.

  • Dual-mode operation allows OS to protect itself and other system components

    • User mode and kernel mode

    • Mode bit provided by hardware

      • Provides ability to distinguish when system is running user code or kernel code

      • Some instructions designated as privileged, only executable in kernel mode

      • System call changes mode to kernel, return from call resets it to user

Distributed systems
Distributed Systems

  • Distributed systems allow users to share resources on geographically dispersed hosts connected via a computer network.

  • The basic types of networks are:

    • Local-area Network (LAN) connects computers within a room, a floor, or a building.

    • Wide-area Network (WAN) links building, cities or countries.

  • A network operating system

    • provides features such as file sharing across the network

    • and includes a communication scheme that allows different processes on different computers to exchange messages

Computing environments
Computing Environments

  • Traditional computing (Centralized computing)

    • Office environment

      • PCs connected to a network, terminals attached to mainframe or minicomputers providing batch and timesharing

      • Now portals allowing networked and remote systems access to same resources

    • Home networks

      • Used to be single system, then modems

      • Now firewalled, networked

Centralized computing is computing done at a central

location, using terminals that are attached to a central


Computing environments cont
Computing Environments (Cont)

  • Client-Server Computing

    • Many systems now servers, responding to requests generated by clients

      • Compute-server provides an interface to client to request services (i.e. database)

      • File-server provides interface for clients to store and retrieve files

Peer to peer computing
Peer-to-Peer Computing

  • Another model of distributed system

  • P2P does not distinguish clients and servers

    • Instead all nodes are considered peers

    • May each act as client, server or both

    • To participate in a P2P system, a node must join P2P network by:

      • Registers its service with centralized lookup service on network,


      • Broadcast request for service and respond to requests for service via discovery protocol