Operating System Introduction for university

What is an operating system?
• A program that acts as an intermediary between a user of a computer and the
computer hardware.
• An operating system is a powerful and usually extensive program that controls
and manages the hardware and other software on a computer.
• All computers and computer-like devices require operating systems, including
laptop, tablet, desktop, smartphone, smartwatch, and router.
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Examples of operating systems
• There are different operating systems that are in use today such as:
• Windows
• Linux and UNIX
• Mac OS
• JunOS, VRP, IOS
• Android OS, iOS, Windows phone OS
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Client and Server Operating Systems
• Desktop Operating Systems (Client Operating System)
• Windows 10, Ubuntu, Mac OS
• Server Operating Systems
• Windows server 2019, Ubuntu Server, UNIX
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Goals of an operating system
• An operating system is usually designed to meet the following goals:
 Execute user programs and solve user problems
 Make the computer system convenient to use
 Use the computer hardware in an efficient manner
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Role of operating system in Computer System
Structure
• Hardware provides basic computing resources such as CPU, memory, I/O
devices.
• Operating system controls and coordinates use of hardware among various
applications and users.
• Application programs are used to solve the computing problems of the users.
• Users are people, machines and other computers.
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Role of operating system in Computer System
Structure
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Open Source & Closed Source Operating Systems
• Open source operating system - Open-source operating system is a type of
computer software in which source code is released under a license in which the
copyright holder grants users the rights to use, study, change, and distribute the
software to anyone and for any purpose.
• Examples of open source operating systems are Linux, Open Solaris, Open BSD,
Free BSD.
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Open Source & Closed Source Operating Systems
• Closed source operating system - Closed-source operating systems use code that
is proprietary and kept secret to prevent its use by other entities. Traditionally, they
are sold for a profit.
• Examples of closed source operating systems are Mac OS, UNIX, Windows.
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Computing Environments
• Traditional computing
• Office environment - PCs connected to a network, terminals attached to
mainframe or minicomputers using time-sharing.
• Home networks - Used to be single system, then modems, now firewalled &
networked.
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• Client-Server Computing
• Dumb terminals supplanted by smart PCs. Many systems such as servers,
responding to requests generated by clients.
Server Computer provides an interface to client to request services (i.e.
database)
File-server provides interface for clients to store and retrieve files.
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• Peer to Peer Computing / Workgroup Computing
• P2P does not distinguish clients and servers
• Instead all nodes are considered peers.
• Each peer may each act as client, server or both;
• A node must join P2P network to use its resources.
• Operating systems used in peer to peer computing are clients which may belong to
same or different vendors.
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• Web based Computing system
• Web has become ubiquitous & PCs are most prevalent devices.
• More devices becoming networked to allow web access.
• Use of operating systems like Windows 95 has evolved into Linux and Windows,
which can be clients and servers.
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• Cloud computing

Cloud computing is the delivery of computing as service rather than a
product.

Cloud computing means storing and accessing data and programs over the
internet instead of your computer's hard drive.

It allows on-demand network access to shared computing resources over the
internet from a remote location.
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What is a User Interface?
• User interface is a medium or the screen thru which a user interacts with an
application, website or an operating system in order to complete the tasks.
• The user interface is of two types
• Command Line Interface (CLI)
• Graphical User Interface (GUI)
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User Interface
• Command Line Interface - CLI allows a user to perform tasks by entering
commands at prompts by using the keyboard keys.
• Its working mechanism is very easy, but it is not user friendly.
• Users enter the specific command, press “Enter”, and then wait for a response.
• After receiving the command, the CLI processes it accordingly and shows the
output/result on the same screen; command line interpreter is used for this
purpose.
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User Interface
• Graphical User Interface - A GUI uses windows, icons, and menus to perform
tasks such as opening, deleting, and moving files.
• Although many GUI operating systems are through the use of a mouse, the
keyboard can also be utilized by using keyboard shortcuts or arrow keys.
• GUI operating systems are much easier to learn and use because commands do not
need memorized.
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Distributed Operating System
• A distributed operating system (DOS) is an essential type of operating system. A
distributed operating system is an extension of the network operating system that
supports higher levels of communication and integration of the machines on the
network.
• This system looks to its users like an ordinary centralized operating system but
runs on multiple, independent central processing units (CPUs).
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• The Distributed operating system involves a collection of autonomous computer
systems, capable of communicating and cooperating with each other through a
LAN / WAN.
• A DOS is used in the distributed system where it manages the system shared
resources used by multiple processes, the process scheduling activity, the
communication and synchronization between running processes etc.
• It is also helps in resource sharing, improves the reliability, communication and
computation speedup.
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• Examples of distributed operating system are:
• LOCUS
• MICROS
• IRIX
• OSF/1
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History of Operating Systems
Generations:
(1945–55) Vacuum Tubes
(1955–65) Transistors and Batch Systems
(1965–1980) ICs and Multiprogramming
(1980–Present) Personal Computers, Tablets, Phones

The First Generation (1945–55) Vacuum Tubes
• Invention of ABC, Z3 computer, Colossus, Mark 1, ENIAC
• Machine language was used
• There were no programming languages
• Computers were enormous & generated much heat
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2nd Generation (1955–65)
Transistors and Batch Systems
• Mainframes were manufactured (Used by large organizations)
• Transistors were used in place of vacuum tubes
• Concept of batch system was there
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3rd Generation (1965–1980)
• Introduction of IC and IBM 360 computers
• Multiprogramming was introduced
• Concept of timesharing was introduced
• MULTICS (MULTiplexed Information and Computing Service)
• Linux and UNIX were written
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4th
Generation (1980–To Date)
PC, Tablets, Phones
• Introduction of VLSI and Microcomputers
• Creation of DOS (Disk Operating System) in 1980's for 80386 & 80486
• Creation of GUI by Apple company
• Windows 95, 98, ME, NT in the 1990's
• And now we have modern technological devices such as ..................
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Virtual Machines
• A virtual machine is a virtual computer that is installed on the host
machine and uses all resources of the host machine. A virtual machine
works the same way as a physical computer.
• A virtual machine uses the memory and processor for executing different
types of programs and carrying out the user and OS tasks.
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Virtual Machines
• The resources of the physical computer are shared to create the virtual machines
and each virtual machine is completely isolated from another VM in order to
protect their system resources.
• A virtual machine is a complete vehicle for operating system R & D.
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Operating system design and implementation
• There are problems in the design and implementation of the operating system and the reasons
are:
• Internal structure of the operating systems vary widely.
• Operating system is designed by defining goals and specifications.
• Choice of hardware and type of system.
• Defining the user goals and system goals
• User Goals - Convenience, easy to learn, reliable, safe and fast
• System Goals - Reliable, error free, efficient, easily designed & implemented
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Operating system design and implementation
• Implementation of an operating system means that how an operating system is written and
installed on the system. Now a days operating systems are written in higher level programming
languages such as C/C++.
• Advantages of higher-level programming languages:
• Development of the operating system is faster and easier to port
• Disadvantages of higher level languages:
• Reduced speed and increased storage requirements
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System Boot
• A motherboard has a program called BIOS which starts when the computer is booted
and it checks RAM, keyboard and other basic devices.
• These basic devices and plug & play devices are also checked to see whether they are
connected or not.
• If the devices present are different from when the system was last booted, the new devices
are configured.
• The BIOS then determines the boot device and the first sector of the boot device is
read and executed.
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System Boot
• This sector contains a program that checks the partition table at the end of the boot
sector to see which partition is active.
• A boot loader is read from active partition which reads the operating system from the
active partition and starts that.
• The operating system queries the BIOS to get the configuration information and then
for each device, it checks and then loads all the device drivers into the kernel.
• The OS initializes its tables, creates background processes and starts up the GUI and a
login program.
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System Programs
• System programs are also known as system utilities. These programs provide a
convenient environment for the execution and development of programs. There
are system programs for the following tasks:
a. File Management & Modification
b. Status Information
c. Data Encryption
d. Communication over the Network
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System Calls
• System call provides an interface to the services made available by the OS and to
understand system calls, we must know about the two modes of OS.
• Kernel Mode 2. User Mode
• If a program runs in user mode, it does not have direct access to resources
(memory, CPU, I/O)
• If a program runs in Kernel mode, it has direct access to the resources.
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System Calls
 Whenever user mode calls to the system that it need certain resources this call is
called the system call.
 System calls are made by the programs that it need resources.
 System call is the programmatic way in which a computer program requests a
service from the kernel of the operating system
 These calls are generally available as routines written in C and C++.
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Types of System Calls
 System calls can be grouped roughly into five major categories
 Process Control System Call: The system calls which happen in process control are:
 End, abort (end: end a process in normal way when it completes it execution and abort we
means to halt abnormally (error occurs).
 Load, execute
 Allocate and free memory
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 File manipulation System Call
 Create file, delete file, Open, close
 Read, write, Get & set file attributes
 Device management System Call
 Request device, release device
 Read, Write
 Logically attach or detach devices
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 Information maintenance system calls: All the information about our system we have made
must be updated.
 Get time or date, set time or date
 Get system data, set system data
 Communication system calls: which are used for communication between different processes or
different devices.
 Create, delete communication connection
 Send, receive messages
 Transfer status information 40

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