Basic operating systems in computer and it's uses

Introduction to Operating System
(OS)
SURYA VISHNURAM

Course Content:
 What is an OS.
 What are its key functions.
 The evaluation of OS.
 What are the popular types of OS.
 Examples

What is an Operating System?
 Computer System = Hardware + Software
 Software = Application Software + System Software(OS)
 An Operating System is a system Software that acts as an
intermediary/interface 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

The Structure of Computer Systems
 Accessing computer resources is divided into layers.
 Each layer is isolated and only interacts directly with the layer below or above it.
 If we install a new hardware device
 No need to change anything about the user/applications.
 However, you do need to make changes to the operating system.
 You need to install the device drivers that the operating system will use to control the new device.
 If we install a new software application
 No need to make any changes to your hardware.
 But we need to make sure the application is supported by the operating system
 user will need to learn how to use the new application.
 If we change the operating system
 Need to make sure that both applications and hardware will compatible with the new OS

CPU – Central Processing Unit
 This is the brain of your computer.
 It performs all of the calculations.
 In order to do its job, the CPU needs commands to perform, and data to
work with.
 The instructions and data travel to and from the CPU on the system bus.
 The operating system provides rules for how that information gets back and
forth, and how it will be used by the CPU.

RAM – Random Access Memory
 This is like a desk, or a workspace, where your computer temporarily stores
all of the information (data) and instructions (software or program code)
that it is currently using.
 Each RAM chip contains millions of address spaces.
 Each address space is the same size, and has its own unique identifying
number (address).
 The operating system provides the rules for using these memory spaces,
and controls storage and retrieval of information from RAM.
 Device drivers for RAM chips are included with the operating system.

Operating System Mode
 The User Mode is concerned with the actual
interface between the user and the system.
 It controls things like running applications
and accessing files.
 The Kernel Mode is concerned with everything
running in the background.
 It controls things like accessing system
resources, controlling hardware functions and
processing program instructions.
 System calls are used to change mode
from User to Kernel.

Kernel
 Kernel is a software code that reside in central core of OS. It has complete control over
system.
 When operation system boots, kernel is first part of OS to load in main memory.
 Kernel remains in main memory for entire duration of computer session. The kernel code is
usually loaded in to protected area of memory.
 Kernel performs it’s task like executing processes and handling interrupts in kernel space.
 User performs it’s task in user area of memory.
 This memory separation is made in order to prevent user data and kernel data from
interfering with each other.
 Kernel does not interact directly with user, but it interacts using SHELL and other programs
and hardware.

Kernel cont…
 Kernel includes:-
1. Scheduler: It allocates the Kernel’s processing time to various processes.
2. Supervisor: It grants permission to use computer system resources to each
process.
3. Interrupt handler : It handles all requests from the various hardware devices
which compete for kernel services.
4. Memory manager : allocates space in memory for all users of kernel service.
 kernel provides services for process management, file management, I/O
management, memory management.
 System calls are used to provide these type of services.

System Call
 System call is the programmatic way in which a computer program/user
application requests a service from the kernel of the operating system on
which it is executed.
 Application program is just a user-process. Due to security reasons , user
applications are not given access to privileged resources(the ones
controlled by OS).
 When they need to do any I/O or have some more memory or spawn a
process or wait for signal/interrupt, it requests operating system to
facilitate all these. This request is made through System Call.
 System calls are also called software-interrupts.

Starting an Operating System(Booting)
 Power On Switch sends electricity to the
motherboard on a wire called the Voltage Good
line.
 If the power supply is good, then the BIOS
(Basic Input/Output System) chip takes over.
 In Real Mode, CPU is only capable of using
approximately 1 MB of memory built into the
motherboard.
 The BIOS will do a Power-On Self Test (POST)
to make sure that all hardware are working.
 BIOS will then look for a small sector at the very beginning of your
primary hard disk called MBR.
 The MBR contains a list, or map, of all of the partitions on your
computer‘s hard disk (or disks).
 After the MBR is found the Bootstrap Loader follows basic instructions
for starting up the rest of the computer, including the operating system.
 In Early Kernel Initialization stage, a smaller core of the Kernel is
activated.
 This core includes the device drivers needed to use computer‘s RAM
chips.

1. Process Management
 A process is a program in execution.
 A process needs certain resources, including CPU time, memory, files, and I/O devices
to accomplish its task.
 Simultaneous execution leads to multiple processes. Hence creation, execution and
termination of a process are the most basic functionality of an OS
 If processes are dependent, than they may try to share same resources. thus task of
process synchronization comes to the picture.
 If processes are independent, than a due care needs to be taken to avoid their
overlapping in memory area.
 Based on priority, it is important to allow more important processes to execute first
than others.

2. Memory management
 Memory is a large array of words or bytes, each with its own address.
 It is a repository of quickly accessible data shared by the CPU and I/O devices.
 Main memory is a volatile storage device. When the computer made turn off everything stored
in RAM will be erased automatically.
 In addition to the physical RAM installed in your computer, most modern operating systems
allow your computer to use a virtual memory system. Virtual memory allows your computer to
use part of a permanent storage device (such as a hard disk) as extra memory.
 The operating system is responsible for the following activities in connections with memory
management:
 Keep track of which parts of memory are currently being used and by whom.
 Decide which processes to load when memory space becomes available.
 Allocate and de-allocate memory space as needed.

3. File Management
 A file is a collection of related information defined by its creator.
 File systems provide the conventions for the encoding, storage and management
of data on a storage device such as a hard disk.
 The operating system is responsible for the following activities in connections
with file management:
✦ File creation and deletion.
✦ Directory creation and deletion.
✦ Support of primitives for manipulating files and directories.
✦ Mapping files onto secondary storage.
✦ File backup on stable (nonvolatile) storage media.

4. Device Management or I/O
Management
 Device controllers are components on the motherboard (or on expansion
cards) that act as an interface between the CPU and the actual device.
 Device drivers, which are the operating system software components that
interact with the devices controllers.
 A special device (inside CPU) called the Interrupt Controller handles the task of
receiving interrupt requests and prioritizes them to be forwarded to the
processor.
 Deadlocks can occur when two (or more) processes have control of different
I/O resources that are needed by the other processes, and they are unwilling to
give up control of the device.

5. Security & Protection
 The operating system uses password protection to protect user data and
similar other techniques.
 It also prevents unauthorized access to programs and user data by
assigning access right permission to files and directories.
 The owners of information stored in a multiuser or networked computer
system may want to control use of that information, concurrent processes
should not interfere with each other.

6. User Interface Mechanism
 A user interface (UI) controls how you enter data and instructions and
how information is displayed on the screen
 There are two types of user interfaces
1. Command Line Interface
2. Graphical user Interface

1. Command-line interface
 In a command-line interface, a user types commands represented by short
keywords or abbreviations or presses special keys on the keyboard to enter data
and instructions

2. Graphical User Interface
 With a graphical user interface (GUI), you interact with menus and visual images

History of Operating System
 The First Generation (1940's to early 1950's)
 No Operating System
 All programming was done in absolute machine language, often by wiring up plug-boards to control the
machine’s basic functions.
 The Second Generation (1955-1965)
 First operating system was introduced in the early 1950's.It was called GMOS
 Created by General Motors for IBM's machine the 701.
 Single-stream batch processing systems
 The Third Generation (1965-1980)
 Introduction of multiprogramming
 Development of Minicomputer
 The Fourth Generation (1980-Present Day)
 Development of PCs
 Birth of Windows/MaC OS

Types of Operating Systems
1. Batch Operating System
2. Multiprogramming Operating System
3. Time-Sharing OS
4. Multiprocessing OS
5. Distributed OS
6. Network OS
7. Real Time OS
8. Embedded OS

1. Batch Operating System
 The users of this type of operating system does not interact with
the computer directly.
 Each user prepares his job on an off-line device like punch
cards and submits it to the computer operator
 There is an operator which takes similar jobs having the same
requirement and group them into batches.

1. Batch Operating System cont..
Advantages of Batch Operating System:
 Processors of the batch systems know how long the job would be when it is in queue
 Multiple users can share the batch systems
 The idle time for the batch system is very less
 It is easy to manage large work repeatedly in batch systems
Disadvantages of Batch Operating System:
 The computer operators should be well known with batch systems
 Batch systems are hard to debug
 It is sometimes costly

2. Multiprogramming Operating System:
 This type of OS is used to execute more than one jobs
simultaneously by a single processor.
 It increases CPU utilization by organizing jobs so that the CPU
always has one job to execute.
 Multiprogramming operating systems use the mechanism of job
scheduling and CPU scheduling.

3. Time-Sharing Operating Systems
 Each task is given some time to execute so that all the tasks work
smoothly.
 These systems are also known as Multi-tasking Systems.
 The task can be from a single user or different users also.
 The time that each task gets to execute is called quantum.
 After this time interval is over OS switches over to the next task.

3. Time-Sharing Operating Systems cont..
 Advantages of Time-Sharing OS:
 Each task gets an equal opportunity
 Fewer chances of duplication of software
 CPU idle time can be reduced
 Disadvantages of Time-Sharing OS:
 Reliability problem
 One must have to take care of the security and integrity of user programs and
data
 Data communication problems.

4. Multiprocessor operating systems
 Multiprocessor operating systems are also known as parallel OS or tightly
coupled OS.
 Such operating systems have more than one processor in close communication
that sharing the computer bus, the clock and sometimes memory and
peripheral devices.
 It executes multiple jobs at the same time and makes the processing faster.
 It supports large physical address space and larger virtual address space.
 If one processor fails then other processor should retrieve the interrupted
process state so execution of process can continue.
 Inter-processes communication mechanism is provided and implemented in
hardware.

5. Distributed Operating System
 Various autonomous interconnected computers communicate with each other using a
shared communication network.
 Independent systems possess their own memory unit and CPU.
 These are referred to as loosely coupled systems.
 Examples:- Locus, DYSEAC

6. Network Operating System
 These systems run on a server and provide the capability to manage data,
users, groups, security, applications, and other networking functions.
 These types of operating systems allow shared access of files, printers,
security, applications, and other networking functions over a small private
network.
 The “ other" computers arc called client computers, and each computer that
connects to a network server must be running client software designed to
request a specific service.
 popularly known as tightly coupled systems.

6. Network Operating System
Advantages of Network Operating System:
 Highly stable centralized servers
 Security concerns are handled through servers
 New technologies and hardware up-gradation are easily integrated into the system
 Server access is possible remotely from different locations and types of systems
Disadvantages of Network Operating System:
 Servers are costly
 User has to depend on a central location for most operations
 Maintenance and updates are required regularly
Examples of Network Operating System are:
Microsoft Windows Server 2003/2008/2012, UNIX, Linux, Mac OS X, Novell NetWare, and BSD, etc.

7. Real-Time Operating System
 These types of OSs serve real-time systems.
 The time interval required to process and respond to inputs is very small.
 This time interval is called response time.
 Real-time systems are used when there are time requirements that are
very strict like
 missile systems,
 air traffic control systems,
 robots, etc.

8. Embaded Operating System
 An embedded operating system is one that is built into the circuitry of an
electronic device.
 Embedded operating systems are now found in automobiles, bar-code scanners,
cell phones, medical equipment, and personal digital assistants.
 The most popular embedded OS
 Windows XP Embedded
 Windows CE .NET:- it supports wireless communications, multimedia and
Web browsing. It also allows for the use of smaller versions of Microsoft
Word, Excel, and Outlook.
 Palm OS:- It is the standard operating system for Palm-brand PDAs as well
as other proprietary handheld devices.
 Symbian:- OS found in “ smart” cell phone

Popular types of OS
 Desktop Class
 Windows
 OS X
 Unix/Linux
 Chrome OS
 Server Class
 Windows Server
 Mac OS X Server
 Unix/Linux
 Mobile Class
 Android
 iOS
 Windows Phone

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