Operating System Concepts Course Instructor Samra Irshad samra

Operating System Concepts

Course Instructor: Samra Irshad samra. irshad@superior. edu. pk Lecturer CS

Objective �To develop an understanding of and appreciation for the role of Operating Systems in Computing Environments 3

• 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. 4

Course requirements �Assignments/Quizes � Written assignments (Small Tasks) (details in coming lectures) � 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 �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 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 software �Hardware components that comprise the physical entity of device �CPU �RAM �I/O devices

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 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. ü Storing an executable program on a secondary storage device such as hard disk ü Loading executable from disk into the main memory ü CPU state appropriately so that program execution could begin ü 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 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

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 ? v Usually produced by I/O devices v Must be handled by the processor by interrupting execution of the currently running process v 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 1. Increased throughput 2. Economy of scale 3. Increased reliability – graceful degradation or fault tolerance

Multi-processing Systems

Multiprocessor systems �Two types of Multiprocessing: 1. 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 Key role – the scheduler

Real-Time Systems n When given an input, O/P must respond in a very well- defined period of time n 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. n 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 ØAllocate appropriate amount of disk space when files are created ØDe-allocate space when files are removed ØEnsure 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 v. 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 (7 th edition) �Computer System Architecture by Morris Mano (3 rd edition)