Download Operating System Concepts

Course Instructor: Samra Irshad
[email protected]
Lecturer CS
Objective
 To develop an understanding of and
appreciation for the role of Operating
Systems in Computing Environments
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•TEXT Book:
 Operating System Concepts by Abraham Silberschatz, Peter B. Galvin
and Greg Gagne
• Reference Books:
 Operating System: Internals and Design principles by William
Stallings.
 Operating Systems by Harvey M. Deitel, Paul J. Deitel, David R.
Choffnes
 No Restriction:
Different Books. You can choose the book of your own choice
• Web Sites & Material:
 will refer you to different web sites and will provide you with different
notes if its required.
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Course requirements
 Assignments/Quizes
 Written assignments (Small Tasks) (details in coming lectures)
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Idea is to initiate research oriented writing not “cut-copy-paste”
 Attendance, Presentations, Quiz & Class Discussion &
Participation (as a regular activity)
 Volunteer presentations (you must not be that familiar with this
kind of stuff but you need to respond to it quickly!)
 Formal Presentations in groups
Examination
 Every thing discussed, during the class or given as reading
material, could be part of the exams
 Questions will be formulated in a way to examine
conceptual thinking
 Other details will be given close to Sessional
Course Contents
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Basic Concepts
Structures and Functions
Process Management
Threads Management
Inter-Process Communication
Synchronization
Deadlocks
Memory Management
Virtual Memory Management
File Systems
I/O Systems
Chapter 1: Introduction
 Basics of Computer Organization and relation with
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operating systems
What is an Operating System?
Multi-programmed Systems
Time shared systems
Real -Time Systems
Multiprocessor Systems
Memory Management
Process Management
Lecture 1
Operating System
 What is an OPERATING SYSTEM ?
 Purpose ? Any raw idea… ?
 Computer System ?
Computer System
 Computer System- why do we use it?
 Allows you to solve problems
 Provides you tools/applications, using those tools
you can develop programs which will ultimately solve
your needs
Computer System
 Computer system is composed of hardware and
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software
Hardware
entity of device
CPU
RAM
I/O devices
components that comprise the physical
Computer Organization basics
 CPU (Central Processing Unit) : Function of this unit ?
 ‘Executes a program’
Contains:
 Arithmetic and Logic Unit for manipulating data
 A number of registers for storing data
 Control circuits for fetching and executing
instructions
CPU Cycle
 CPU cycle- Fetching, Decoding and Executing
 Fetching an instruction- CPU reads an instruction from
memory
 Decoding an instruction- determining what actions
the instruction require
 Executing- carrying out those actions
Memory
 Where all the programs/data is stored ?
 Web browsers, word processor etc…
 Initially data/program is stored in ‘disk storage’, (also
known as ‘secondary memory’).
 For a program to run/execute, it must reside in ‘MAIN
MEMORY’ (RAM)
Secondary Storage
 Secondary Storage- as an extension to main memory
 Why not store the programs and data all at once in main
memory ?
 Types of storage devices
Registers, cache, main memory, electronic disk, magnetic
disk, magnetic tapes
RAM
 RAM: Random Access Memory..
 Why called Random Access Memory ?
 Program is brought into main memory from
secondary storage so that it can be executed
 CPU can access ANY location in memory at random
and retrieve information within a fixed interval of time
‘Word’ as an entity
Execution of a program
 Primary purpose of a computer system is to generate executable
programs and execute them.
 Following are some of the main issues involved in performing
these tasks.
 Storing an executable program on a secondary storage
device such as hard disk
 Loading executable from disk into the main memory
 CPU state appropriately so that program execution could begin
 Multiple processes, synchronizing their access to shared
data, and allowing them to communicate with each other
I/O devices
 I/O devices: Human interaction with the system
through Input/output devices
 Real-time data
 Computer Organization: the way hardware
components operate and the way they are connected
together to form a computer system
 Hardware components: CPU, Memory and I/O
Motivation for OS
 If we have only the computer hardware system, what
we can do with it ?
 What are the things required to make a computer
system ‘ACTUALLY’ useful ?
Operating System
A platform/software needed .. Is
it so ?
Operating System Basics
 Now coming to Operating Systems…..
 Essential part of a computer system
 Provides services to computer user
 To make more effective use of computer
 Why do we study it?... To get the knowledge of services
provided by operating system
 E.g. A high-level language program written by user to
solve data-processing tasks is an application
program while the compiler that translates the
program into machine language is task of operating
system
Layered Structure
Multiprogrammed Systems
 Several jobs are kept in main memory at the same time,
and the CPU is multiplexed among them.
Multi-programmed Systems
 Job pool
 Job-scheduling
 CPU scheduling
OS Features Needed for
Multiprogramming
 Memory management – the system must allocate the
memory to several jobs.
 CPU scheduling – the system must choose among several
jobs ready to run.
Time-Sharing Systems- Interactive
Computing
 Multi-programmed systems did not provide user interaction
 The CPU executes multiples jobs by switching among them
 Switches occur frequently
Each job is allocated a small portion of CPU time
 On-line communication between the user and the system is provided
 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 is swapped in and out of memory to the disk
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Bootstrap program
 Bootstrap
program:
A program whose
function is to start the computer software
operating when the power is turned on.
 Loads a portion of OS to main memory
and control is then transferred to OS
which prepares the computer for general use
Interrupts and Traps
 Interrupts- Interrupting the normal execution of
processor… Examples ?
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Usually produced by I/O devices
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Must be handled by the processor by interrupting
execution of the currently running process
 Traps- Events produced by execution of certain
instructions…. Examples ?
 Load and Store Instructions
 Von-neumann Architecture VS Harvard Architecture
 Volatile VS Non-volatile
Storage Device
Hierarchy
Computer-System Architecture
 Single processor systems
 Single CPU
 Can also include I/O processor e.g. disk controller
processor
 Multiprocessors systems
Also known as parallel systems, tightly-coupled systems
 Advantages include
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Increased throughput
Economy of scale
Increased reliability – graceful degradation or fault
tolerance
Multi-processing Systems
Multiprocessor systems
Key role – the scheduler
 Two types of
Multiprocessing:
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Asymmetric Multiprocessing
assigns certain tasks only to certain
processors, Master-slave concept…
Master processor schedules and
allocates work to the slave processors
1.
Symmetric Multiprocessing treats all of the processing elements
in the system identically
Real-Time Systems
 When given an input, O/P must respond in a very well-
defined period of time
 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.
 Real-Time systems may be either hard (guarantees that
critical tasks be completed on time, if not then catastrophe
may happen) or soft real-time (no fear of catastrophe)
Operating System- A Resource
Manager
 Resource Manager: Resources- CPU,
Memory and I/O
Secondary Storage Management
Manage secondary storage devices
Allocate appropriate amount of disk space when
files are created
De-allocate space when files are removed
Ensure that a new file does not overwrite an
existing file
Main Memory Management
Manage primary storage (main memory)
 Allocate appropriate amount of memory space when programs
are to be loaded into the memory for execution
 De-allocate space when processes terminate
 Ensure that a new program is not loaded on an existing program
 Minimize the amount of unused memory space
 Allow execution of programs larger in size than the available
main memory
Virtual Memory
Processes
 A program in execution is called a process
 Single-user and Multiple users
 In case of multiple processes, how the CPU will be
allocated to those evenly ?
 Some processes getting maximum of CPU time while
others are being allocated less ?
 CPU-time scheduling
Process Management
Manage processes
Allow simultaneous execution of processes by
scheduling the CPU
 Prevent deadlocks between processes
 Ensure integrity of shared data
 Synchronize executions of cooperating processes
References
 Operating System Concepts by Silberschatz (7th
edition)
 Computer System Architecture by Morris Mano (3rd
edition)