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Operating
Systems
Objective
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The historic background
What the OS means?
Characteristics and types of OS
General Concept of Computer
System
A Computer System consists
of five components, namely,

Hardware
 provides
the basic resources including CPU,
Memory, Harddisk, etc.

Application programs
 define
the ways in which resources are used to
solve the problems of the users
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Users
 to
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OPERATING SYSTEMS (OS)
 to
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use the system
operate the system
Document
policy to guide the application
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How can application programs make use of
hardware resources?
How to move a program from disk to main
memory?
How can a character be read in from the
keyboard and is displayed on the screen?
How to control a printer for printing a file?
Operating systems provide a link between
application programs and the hardware.
What Operating Systems
can do?
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Program modules within a computer
system that govern the control of system
resources
OS is a resource manager which:
 Keeps
track of the resources
 Enforces policy that determines who get
what, when, and how much
 Allocates resources
 Reclaims resources
Terminology
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Resource
 Is a commodity necessary to get work done. This includes
the disk drives, CPUs, etc.
Process
 Is a fundamental entity that requires resources to
accomplish, basically a program in execution.
Command Interpreter
 It is a special process that reads commands from a terminal..
Thread
 sometimes called a lightweight process (LWP). It is a basic
unit of CPU utilisation
Historical Developments

Stage one
 The
computer systems at that time were massive,
expensive and difficult to use.

Stage Two, Operator-driven
 In
an effort to avoid idleness, an operator was
hired to perform the repetitive tasks

Stage 3 Off-line
 Much
of the operator’s job was mechanical. The
next stage was to automate that job
Historical Development.

Stage Four, Spooling
 At
this stage, disks were introduced as a
secondary storage medium.
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Stage five, Multiprogramming
 having
more than one job by partitioning the
main store into several pieces,
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Stage Six, Time sharing system
 called
multi-tasking and is a logical extension
of multiprogramming.

Stage Seven, Distributed Systems
 The
more recent development focuses on
distributed computing.
Spooling
Multiprogramming
Time sharing
Structure of Operating
systems
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There are four different structures
as given below:
Monolithic system
Layered System
Virtual Machine
Client-server model
OS Components
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Process Management
Memory Management
Secondary Storage Management
I/O System
Protection System
Command Interpreter System
Monolithic
Layered
Virtual Machine
Client-server
Future trend
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Multiprocessing will become much more
common.
Hardware architectures of the future will
distribute control into localized processors.
Languages are being developed to exploit
concurrency
Massive parallelism will become common
will be designed to foster (foster means help) the
operation of virtual machines
Developments in software engineering will result
in more maintainable
Classification of
Operating System
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Off-line, Batch and Remote batch
On -line, Time sharing
Personal computing, User
progammable
Data base, Real time
Non-programmable, Multi-user
single user, System features
Characteristics of OS
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Have priority over user programs
Manage input, output, memory and
CPU (Data entry, output to printer)
Increase computer system
efficiency
Sequence and schedule programs
Handle hardware errors and
pProvide security for user
programs
Windows 95/98 - Outline
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Win95 was released in August
1995
Total rewrite and replacement for
Windows 3.x
Windows-95 “backwards
compatible” with software from
earlier O/S
Major, modern features include
Summary
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Compatibility
 It means that the ideal operating system is designed to provide
execution environments for applications for other operating
systems.
Portability
 It means that the operating system can be ported to a variety of
different machines
Robustness
 It means that the ideal operating system can provide protection
from accidental or deliberate damage by user programme
Usability
 Easy to use, click and drag are more friendly than DOS prompt
commands
Summary
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Efficiency
 The system functions quickly, makes optimum use of the resources
Flexibility
 Adaptability to a specific environment, like Unix can be in
Minicomputer or PC
Transparency
 Users are unaware of all details they need not know
Security
 Protecting data from unauthorized access
Integrity
 Protecting itself and users from damage or any other ill effect of
other’s error or malice.