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.

Resource allocator Graphical Interface between user and

computerOperating System Concepts

WHAT IS AN OPERATING SYSTEM

The features in any OS may vary greatly in terms of space and graphics

Commonly, Operating systems can also be defined as “one program running at all times on the computer”.

Operating System Concepts

ELEMENTS OF OPERATING SYSTEM

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).

Operating System Concepts

Operating System Concepts

OPERATIONS PERFORMED

When a computer is powered up—bootstrap program residing in ROM--loads the OS into memory

Initialization of a system– CPU registers, device controllers, memory content

Starts execution of its first process and waits for some event (called interrupt) to occur.

When CPU is interrupted, it stops what it is doing and immediately transfers execution to a fixed location (starting address).

STORAGE STRUCTURE

The CPU can load instructions only from memory i.e. main-memory or volatile memory, so any programs to run must be stored there.

Also, the secondary storage is able to hold large quantity of data permanently.

So, most application programs and system i.e. OS are stored on a disk until they are loaded into memory.

EVOLUTION OF OPERATING SYSTEMS

Serial Processing (1950) Batch Processing (1960) Single-User Multi-User Multi Programming Time Sharing (Multi Tasking) Parallel System Distributed System

SERIAL PROCESSING SYSTEM

- bring cards to 1401- read cards to tape- put tape on 7094 which does computing- put tape on 1401 which prints output

Operating System Concepts

BATCH PROCESSING SYSTEM

Same type of jobs are batched together and execute at a time.

The carrier carries the group of jobs at a time from one room to another.

The programmer need not running between 3 rooms several times.

Batch Systems are used for running batch operations such as calculating and printing customers' bills.

They often run a single task for hours or even days at a time, eg: banks process millions of cheques each month. These are processed together in a long run, usually overnight.

Operating System Concepts

TYPES OF OPERATING SYSTEM

Single User (Single Processor System)

Single user operating' system allows a single user to access the computer at a time.

This type of operating system is mostly used on computers having single processor such as PCs.

In single user operating system, the CPU remains idle during an I/O operation. So the CPU utilization is reduced.

Operating System Concepts

SINGLE USER OPERATING SYSTEM

2 types of single user operating systems

i. Single-User Single Tasking Operating System:

This system allows a single user to execute one program at a time. MS-DOS is an example of this kind of operating system.

ii. Single-User Multitasking Operating System: This system allows a single user to execute

multiple programs at the same time on a computer.

For example, in Windows you can load multiple programs at a time such as Ms-Excel, Ms-Word, Ms-Access as well as you can listen the music.

Operating System Concepts

MULTI PROGRAMMING It is a technique to execute number of programs

simultaneously by a single processor. Number of processes reside in a main memory

and CPU picks and begins to execute one of them .

Operating System Concepts

MULTI PROGRAMMING Advantages:

Efficient memory Utilization CPU is never idle. So performance of CPU will increase. Throughput of CPU may also increase. In non-multiprogramming (mono programming ), the

user/ program has to wait for CPU much time.

Operating System Concepts

MULTI USER(MULTI PROCESSOR OR PARALLEL SYSTEMS)

o These systems have two or more processors in close communication, sharing the computer bus and sometimes the clock, memory, and peripheral devices. Such systems are referred as “Tightly coupled” systems.

o Multi-User operating systems are used on networked systems.

Operating System Concepts

MULTI USER(MULTI PROCESSOR OR PARALLEL SYSTEMS) 3 types of multi user systems

i. Single Processor systems have only a single processor or CPU, which is shared between users by dividing the CPU time into time-slices and allocating one of these to each user in turn. The time-slices are very short, giving each user the impression that their programs are running continuously.

ii. Multiple Processor systems have more than one processor. Users still have to share processors, but performance is improved as there are fewer users per processor.

iii. Networked Systems (Clustered systems) consist of single user PCs connected together to form a Local Area Network (LAN). Each PC has a Network Interface Card (NIC)and they are normally connected by means of copper or fibre cables. Networks allow users to share files and resources such as a printer or an Internet connection. Common network operating systems include Windows NT, Windows 2000/2003 Server and Unix/Linux.

MULTI USER(MULTI PROCESSOR OR PARALLEL 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

ADVANTAGES

Increase throughput (more work done in less time)

Economy of scale Increased reliability (in case of failure)

TIME SHARING

It is a logical extension of multiprogramming. Multiple jobs are executed by the CPU

switching between them. 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 at regular time interval.

Time slots are defined by operating system.

Operating System Concepts

DISTRIBUTED SYSTEMS

In distributed systems, the processor can’t share memory or a clock, each processor has its own local memory.

The processor communicate with one another through various communication lines such as high speed buses.

These type of systems are referred as loosely coupled.

Advantages: Resource Sharing Computation Speed up. Reliability Communication

Operating System Concepts

REAL TIME SYSTEM

Real Time operating System is used when rigid time requirements.

A Real Time system has well defined, fixed time constraints.

A processing must be done within a specified time constraints or the system will fail.

A real time system runs correctly if it returns the correct result within its time constraints.

2 types: Hard real time system Soft real time system

Operating System Concepts

HANDHELD SYSTEMS

Handheld Systems include personal digital assistants or cellular telephones with connectivity to a network such as the Internet.

Handheld systems have a small amount of memory, slow processors and feature, and small display screen.

Issue: Speed of the processor Small amount of memory Small display screen

Operating System Concepts

FUNCTIONS OF OS Program Creation

The OS provides editors, debuggers, to assist the programmer in creating programs.

Program Execution To execute a particular program , OS perform several task

for e.g. loading of data and instruction in main memory, Initialization of file and other resources .

I/O operation A running program may require input and output. This I/O

may involve a file or an I/O device. A user program can not execute I/O operations directly. It is done by OS.

Error Detection The operating system detects the different types of errors

and should take appropriate action. The error include , power failure, printer out of paper,

illegal instruction in the program(division by zero, arithmetic overflow)

Operating System Concepts

FUNCTIONS OF OSResource Allocation

The OS collects all the resources in the network environment or a system and grant these resources to requested process.

The resource include CPU cycles, main memory , i/o devices, file storage and so on.

Accounting The OS can keep track of which user use how much

and what kind of computer resources . This record keeping is useful to improve computing

resources.

Protection The OS provides security mechanism to protect the

unauthorized usage of files in the network environment.

Operating System Concepts

OS AS A RESOURCE MANAGER

LAYERED APPROACH

The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface.

With modularity, layers are selected such that each layer uses functions (operations) and services of only lower-level layers.

This approach simplifies debugging and system implementation.

The first layer can be debugged without concern for the rest of the system, because it uses basic hardware to implement its functions. Once that layer is debugged, its correct functioning can be assumed while the second layer is debugged.

Each layer is implemented only those operations provided by lower layers.

Operating System Concepts

LAYERED APPROACH

A layer does not need to know how these operations are implemented, it need to know only what these operations do.

Each layer hides existence of certain data structures, operations and hardware from higher level layers.

A major difficulty with this approach is that each layer should be identified carefully because above layer depends on that.

Operating System Concepts

THE OPERATING SYSTEM LAYER

Operating System Concepts

OS LAYER STRUCTURE

Operating System Concepts

VIRTUAL MACHINE

A virtual machine takes the layered approach to its logical conclusion. It treats hardware and the operating system kernel as though they were all hardware.

The fundamental idea behind a virtual machine is to abstract the hardware of a single computer into several different execution environments, thereby creating the illusion of multiple processes, each executing on its own processor with its own (virtual) memory.

A virtual machine provides an interface identical to the underlying bare hardware.

Operating System Concepts

VIRTUAL MACHINE The resources of the physical computer are shared

to create the virtual machines. CPU scheduling can create the appearance that users

have their own processor. Spooling and a file system can provide virtual card

readers and virtual line printers. A normal user time-sharing terminal serves as the

virtual machine operator’s console.

Operating System Concepts

SYSTEM MODEL

Operating System Concepts