Operating System.pdf topic of interprocess comunication

Introduction to Operating System (OS)

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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

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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 operating system.

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Computer Architecture
Special busses (roads) connecting
all input/output devices to
motherboard.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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BIOS
• BIOS firmware was stored in a ROM/EPROM (Erasable Programmable
Read-Only Memory) chip known as firmware on the PC motherboard.
• BIOS can be accessed during the initial phases of the boot procedure by
pressing del, F2 or F10.
• Finally, the firmware code cycles through all storage devices and looks for
a boot-loader. (usually located in first sector of a disk which is 512 bytes)
• If the boot-loader is found, then the firmware hands over control of the
computer to it.

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Functions of Operating System

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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.

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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.

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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.
 FAT12 (floppy disks)
 FAT16 (DOS and older versions of Windows)
 FAT32 (older versions of Windows)
 NTFS (newer versions of Windows)
 EXT3 (Unix/Linux)
 HFS+ (Max OS X)
• 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.

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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.
• It performs the following activities for device management.
 Keeps tracks of all devices connected to system.
 Designates a program responsible for every device known as Input/output controller.
 Decides which process gets access to a certain device and for how long.
 Allocates devices in an effective and efficient way.
 Deallocates devices when they are no longer required.

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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.

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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

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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

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

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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

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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

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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.

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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
 The other jobs will have to wait for an unknown time if any job fails
Examples of Batch based Operating System:
IBM's MVS

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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.

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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.

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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 problem
• Examples of Time-Sharing Oss
Multics, Unix, etc.

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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.

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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

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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.

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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.

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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.

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8. Embedded 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 operating systems for consumer products, such as PDAs,
include the following:
 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 phones from Nokia and Sony Ericsson

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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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Desktop Class Operating Systems:-
• Platform: the hardware required to run a particular
operating system
– Intel platform (IBM-compatible)
• Windows
• DOS
• UNIX
• Linux
– Macintosh platform
• Mac OS
– iPad and iPhone platform

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MS-DOS
• Single User Single Tasking OS.
• It had no built-in support for networking, and users had to manually install
drivers any time they added a new hardware component to their PC.
• DOS supports only 16-bit programs.
• Command line user interface.
• So, why is DOS still in use? Two reasons are its size and simplicity. It does
not require much memory or storage space for the system, and it docs not
require a powerful computer.

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Microsoft Windows
• The graphical Microsoft operating system designed for Intel-platform desktop
and notebook computers.
• Best known, greatest selection of applications available.
• Current editions include Windows 7, 8, 8.1 and 10.

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Mac OS
• User-friendly, runs on Mac hardware. Many applications available.
• Current editions include: Sierra, High Sierra, Mojave, Catalina & Big Sur—Version
XI(Released in Nov 2020)

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Linux
• Linux: An open-source, cross-platform operating system that runs on
desktops, notebooks, tablets, and smartphones.
– The name Linux is a combination Linus (the first name of
the first developer) and UNIX (another operating system.
• Users are free to modify the code, improve it, and redistribute it,
• Developers are not allowed to charge money for the Linux kernel itself
(the main part of the operating system), but they can charge money for
distributions (distros for short).

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Google Chrome OS
• Chrome OS. Is a popular thin client operating system.
• Thin client A computer with minimal hardware, designed for a specific task.
For example, a thin web client is designed for using the Internet.

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Server Operating Systems
• Windows Server
– Familiar GUI interface for those experienced with Windows
• UNIX
– Very mature server capabilities, time-tested, large user
community, stable
• Linux
– Free, customizable, many free services and utilities available

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Tablet and Phone Operating Systems
• System-on-chip (SoC): An operating system that comes preinstalled on a
chip on a portable device such as a smartphone.
• Popular SoC operating systems:
 iOS: for iPad, iPhone
 Android: for a variety of tablets and phones
• Downloadable applications (apps) from an App store, for example:
 Apple App Store
 Google Play Store

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iOS on the iPhone and iPad
• The Apple-created operating system for Apple tablets and phones.
• The current stable version, iOS 14, was released to the public on September
16, 2020.

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Android
• Android, a popular OS for smartphones and tablets, is
based on Linux Kernel.
– Developed by Google
• Current versions include:
– Android 8 Oreo
– Android 9 Pie
– Android 10
– Android 11 (released on Sep, 2020)

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