NE223_chapter 1_Overview of operating systems.ppt

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Network Operating Systems
Chapter 1: Overview of Operating
Systems

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Content
1. What is an Operating System?
2. History of Operating Systems
3. Components and Structures of Computer Systems
4. Main functions of Operating System
5. Types of Operating Systems
6. Interfaces of Operating Systems
7. Operating System Mode

 Operating System definition:
 An Operating System is a software that
acts as an interface between the computer
hardware components and the user.
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 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.

 Some examples of Operating Systems:
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2. 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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3. Components and Structures of
Computer Systems
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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USER
APPLICATIONS
OPERATING
SYSTEM
HARDWARE

Operating System
 Accessing computer resources is divides 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 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.
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USER
APPLICATIONS
OPERATING
SYSTEM
HARDWARE

Operating System
 If we install a new software application:
 No need to make any changes to your hardware,
 But you need to make sure that 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 be compatible with the new operating system.
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USER
APPLICATIONS
OPERATING
SYSTEM
HARDWARE

4. Main Functions of Operating
System
 Some typical operating system functions may include managing memory,
files, processes, I/O system and devices, security.
 Below are the main functions of operating system:
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System
 Memory Management: Performs the task of allocation and de-allocation of
memory space to programs in need of this resources.
 Process Management: Helps OS to create and delete processes. It also
provides mechanisms for synchronization and communication among
processes.
 File Management: Manages all the file-related activities such as organization
storage, retrieval, naming, sharing and protection of files.
 Device Management: Keeps tracks of all devices. This module also
responsible for this task is known as the I/O controller. It also performs the task
of allocation and de-allocation of the devices.
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System
 I/O System Management: One of the main objects of any OS is to hide the
peculiarities of that hardware devices from the user.
 Secondary-Storage Management: Systems have several levels of storage
which includes primary storage, secondary storage, and cache storage.
Instructions and data must be stored in primary storage or cache so that a
running program can reference it.
 Security: Security module protects the data and information of a computer
system against malware threat and authorized access.
 Command interpretation: This module is interpreting commands given by the
and acting system resources to process that commands.
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System
 Networking: A distributed system is a group of processors which do not share
memory, hardware devices, or a clock. The processors communicate with one
another through the network.
 Communication Management: Coordination and assignment of compilers,
interpreters, and another software resource of the various users of the computer
systems.
 Job Accounting: Keeping track of time & resource used by various job and
users.
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Following are the popular types of OS:
 Batch Operating System
 Multitasking/Time Sharing OS
 Multiprocessing OS
 Real Time OS
 Distributed OS
 Network OS
 Mobile OS
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 Batch Operating System: Some computer processes are very lengthy and
time-consuming. To speed the same process, a job with a similar type of needs
are batched together and run as a group.
The user of a batch operating system never directly interacts with the computer.
In this type of OS, every user prepares his or her job on an offline device like a
punch card and submit it to the computer operator.
 Multitasking/Time Sharing OS: Time-sharing operating system enables
people located at a different terminal(shell) to use a single computer system at
the same time. The processor time (CPU) which is shared among multiple users
is termed as time sharing.
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 Multiprocessing OS: Are also known as parallel OS or tightly coupled OS. It
executes multiple jobs at the same time, makes the processing faster and
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.
 Real time OS: A real time operating system time interval to process and
respond to inputs is very small. Examples: Military Software Systems, Space
Software Systems are the Real time OS example.
 Distributed OS: Distributed systems use many processors located in different
machines to provide very fast computation to its users.
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 Network OS: Network Operating System runs on a server. It provides the
capability to serve to manage data, user, groups, security, application, and
other networking functions.
 Mobile OS: Mobile operating systems are those OS which is especially that are
designed to power smartphones, tablets, and wearables devices.
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A user interface (UI) controls how you enter data and
instruction and how information is displayed on the
screen.
 There are two types of user interfaces:
A. Command Line Interface
B. Graphical User Interface
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A.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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B. Graphical User Interface
With a graphical user interface (GUI), user interacts with
menus and visual images.
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 The User Mode is concerned with the actual
interface between the user and the system.
 It controls things like running applications
and accessing files.
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 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.
 It controls things like running applications
and accessing files.
 System calls are used to change mode from
User to Kernel.

A. Kernel
 Kernel is a software code that reside in central core of OS.
It has complete control aver 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 into
protected area of memory.
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 Kernel performs its task like executing processes and
handling interrupts in kernel space.
 User performs its 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 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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B. 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).
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 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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