Overview of Operating System -...

OVERVIEW OF

OPERATING SYSTEM Slides by: Ms. Shree Jaswal

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Slides by: Ms. Shree Jaswal 1

Topics to be covered:

• Operating system objectives and functions, Evolution of

OS, Characteristics of modern OS,

• Basic concepts: Processes, Files, System calls, Shell,

• Kernel architectures: Monolithic, Micro-kernel, Layered,

• Kernel mode of operations

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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.

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The Operating System as an Extended

Machine

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Operating systems turn ugly hardware into beautiful abstractions.

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

• Users

• People, machines, other computers

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Layers and Views

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Services Provided by the OS

• Program execution

• Access I/O devices

• Controlled access to files

• System access

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Services Provided by the OS

• Error detection and response

• Internal and external hardware errors

• Software errors such as arithmetic overflow and inability to grant

request of an application

• Accounting

• Collect usage statistics

• Monitor performance

• Used to anticipate future enhancements

• Used for billing purposes

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Operating System as a Resource Manager

• Responsible for managing resources

• Functions same way as ordinary computer software

• It is a program that is executed by the processor

• Operating system frequently relinquishes control and

must depend on the processor to allow it to regain control

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OS as Resource Manager

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Kernel

• Portion of operating system that is in main memory

• Contains most frequently used functions in the OS and at

a given time other portions of the OS currently in use.

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Evolution of Operating Systems

• Reasons for evolution of OS are:

• Hardware upgrades plus new types of hardware

• Device drivers

• New services

• Fixes

• Mostly: security fixes!

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EVOLUTION OF OPERATING

SYSTEMS

… a bit of history…

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1 - Serial processing systems

• They are called so due to the fact that users have access to the

computer in series.

• No operating system

• Machines run from a console with display lights, toggle switches,

input device, and printer

• Programs in machine code were loaded via the input device (eg. A

card reader)

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Example of card: Bell Telephone

Laboratories GE 600

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This card, probably designed in October 1965 (judging by the notation

"10-65" printed on the left edge), was printed for use with the GE 600

series computers at Bell Labs.


• These early systems presented 2 main problems:

• Scheduling: most installations used a hard copy sign-up sheet to

reserve machine time.

• Setup time: Setup included loading the compiler, source program,

saving compiled program, and loading and linking. Thus

considerable amount of time was spent in just setting up the

program to run.

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2 - Simple batch system

• Monitor

• Software that controls the sequence of events

• Improves job setup time

• Batch jobs together – job control language (JCL)

• Program returns control to monitor when finished

• Hardware support for the monitor model

• Memory protection: some memory areas are accessible only to

the monitor

• Privileged mode instructions: only accessible to the monitor

• Interrupts (early machines did not have this)

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An early batch system

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An early batch system.

(a) Programmers bring cards to 1401.

(b)1401 reads batch of jobs onto tape.


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(c) Operator carries input tape to 7094.

(d)7094 does computing.

(e) Operator carries output tape to 1401.


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(f) 1401 prints output.

IBM 7094

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Uniprogramming

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

proceeding

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Multiprogramming

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

switch to the other job

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Multiprogramming

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Time Sharing Systems

• Using multiprogramming to handle multiple interactive

jobs

• Processor’s time is shared among multiple users who

simultaneously access the system through terminals

• If there are ‘n’ users actively requesting service at one

time each user will only see on the average ‘1/n’ of the

effective computer speed.

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Batch Multiprogramming versus Time

Sharing

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Major achievements of operating systems

1. Processes

2. Memory management

3. Information protection and security

4. Scheduling and resource management

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1. Process

It is defined as:

• A program in execution

• An instance of a program running on a computer

• The entity that can be assigned to and executed on a

processor

• A unit of activity characterized by

• A single sequential thread of execution

• A current state

• An associated set of system resources

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1. Process

• Consists of three components

• An executable program

• Associated data needed by the program

• Execution context of the program

• All information the operating system needs to manage the process

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Process

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2. Memory Management

• Process isolation

• Automatic allocation and management

• Protection and access control

• Support of modular programming

• Protection and access control

• Long term storage

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Virtual Memory

• Allows programmers to address memory from a logical

point of view

• Allow the illusion of operating with a larger memory space

than what is available in reality

• By storing some of the information on the file system

• It is used to meet the requirement of having multiple user

jobs reside in main memory concurrently

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Paging

• One way to implement virtual memory

• Allows the process to be comprised of a number of fixed-size blocks, called pages

• Virtual address is a page number and an offset within the page

• Each page may be located anywhere in main memory

• Real address or physical address is the main memory address

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Virtual memory addressing

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3. Information Protection and Security

• Availability

• Concerned with protecting the system against interruption

• Confidentiality

• Assuring that users cannot read data for which access is

unauthorized

• Data integrity

• Protection of data from unauthorized modification

• Authentication

• Concerned with the proper verification of the identity of

users and the validity of messages or data

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4. Scheduling and Resource

Management

• Fairness

• Give equal and fair access to resources

• Differential responsiveness

• Discriminate among different classes of jobs

• Efficiency

• Maximize throughput, minimize response time, and accommodate

as many uses as possible

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Key Elements of an Operating System

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Traditional OS structure

• monolithic/layered systems

one/N layers all executed in “kernel-mode”

good performance but rigid

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OS kernel

hardware

user

process

file

system

memory

system

user

system calls

Monolithic Systems

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A simple structuring model for a monolithic system.

Modes of OS

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Modern Operating Systems

• Microkernel architecture

• Assigns only a few essential functions to the kernel

• Address spaces

• Interprocess communication (IPC)

• Basic scheduling

• It interacts with local and remote server processes in

the same way facilitating construction of distributed

systems.

• Working examples Mach, QNX

• Current operating systems: Windows, Linux, Mac OS

are not microkernel based

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Micro-kernel OS

client-server model, IPC between clients and servers

the micro-kernel provides protected communication

OS functions implemented as user-level servers

flexible but efficiency is the problem

easy to extend for distributed systems

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micro-kernel

hardware

memory

server

IPC

user mode client

process file

server

memory

server

Microkernels

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Structure of the MINIX 3 system

Extensible OS kernel

user processes can load customized OS services into

the kernel

good performance but protection and scalability become

problems

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extensible kernel

hardware

process user mode

process process

my

memory

service

default

memory

service

Characteristics of Modern Operating

Systems • Multithreading

• Process is divided into threads that can run concurrently

• Thread

• Dispatchable unit of work

• Executes sequentially and is interruptable

• Process is a collection of one or more threads

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Systems • Symmetric multiprocessing (SMP)

• There are multiple processors

• These processors share same main memory and I/O facilities

• All processors can perform the same functions

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Multiprogramming and Multiprocessing

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Systems • Distributed operating systems

• Provides the illusion of a single main memory space and single

secondary memory space

• Eg. Amoeba by Andrew Tannembaum

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Systems • Object-oriented design

• Used for adding modular extensions to a small kernel

• Enables programmers to customize an operating

system without disrupting system integrity

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Computer Hardware Review

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Some of the components

of a simple personal computer.

Processors

• CPU is brain of the computer

• Has :

• general registers

• Program counter

• Stack pointer

• Program status word (PSW)

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Operating System Concepts

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(a) A three-stage pipeline. (b) A superscalar CPU.

Memory

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A typical memory hierarchy.

The numbers are very rough approximations.

Memory

• Cache memory transparently stores data so that future requests for that data can be served faster.

• The data that is stored within a cache might be values that have been computed earlier or duplicates of original values that are stored elsewhere

• If requested data is contained in the cache (cache hit), this request can be served by simply reading the cache, which is comparatively faster

• Otherwise (cache miss), the data has to be recomputed or fetched from its original storage location, which is comparatively slower

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Memory

• Main memory is often called RAM

• RAM, DRAM, DDR SDRAM and SRAM are volatile forms

of memory

• ROM, PROM, EPROM, EEPROM are non volatile forms

of memory

• CMOS is volatile memory used to hold current date and

time

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Disks

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Structure of a disk drive.

I/O Devices

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(a) The steps in starting an I/O device and

getting an interrupt.

I/O Devices

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(b) Interrupt processing involves taking the

interrupt, running the interrupt handler,

returning to the user program.

Buses

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The structure of a large Pentium system


• Associated with each process is its address space, a list

of memory locations from some min(usually 0) to some

max, which the process can read & write

• The address space contains the executable program, the

program’s data and its stack.

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• When a process is suspended temporarily, it must later

be restarted in exactly the same state it had when it was

stopped.

• For this, all the info about each process, other than its

own address space is stored in an OS table called the

process table, which is an array of structures, one for

each process in existence.

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Processes

• If a process can create one or more other processes &

these processes in turn can create child processes we

arrive at a process tree structure

• IPC: Related processes that are cooperating to get some

job done often need to communicate with one another &

synchronize their activities. This communication is called

interprocess communication.

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Processes

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A process tree. Process A created two child processes, B and

C. Process B created three child processes, D, E, and F.

Files

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A file

system for

a university

department

.

Files

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(a) Before mounting, the files on the CD-ROM are not accessible. (b)

After mounting, they are part of the file hierarchy.

Files

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Two processes connected by a pipe.

System Calls

• Interface between user programs and

OS

• Vary from OS to OS

• Example of system call

• Count=read(fd, buffer, nbytes)

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System Calls

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The 11 steps in making the

system call

read(fd, buffer, nbytes).

Memory Layout

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Processes have three segments:

text, data, and stack.

UNIX

• Hardware is surrounded by the operating-system

• Operating system is called the kernel

• Comes with a number of user services and interfaces

• shell

• C compiler

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General UNIX architecture

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UNIX

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Modern UNIX Systems

• System V Release 4 (SVR4)

• Solaris 2.x

• 4.4BSD

• Linux

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THANK YOU!

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