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perating System (OS)
A collection of software written to provide the fundamental instructions that a computer needs to manage
resources, such as memory, the file system, and processes is called an Operating System. In other words,
is a master program that controls a computer's basic functions and allows other programs to access the
computer's resources such as disk drive, printer, keyboard, and screen.
Examples of operating systems include MS Windows 95, MS Windows NT, Windows X
P, UNIX, DOS and
Functions of Operating System:
The main functions of OS are:
It manages the hardware and software resources of the system. In a
, these resources
things as the
, disk etc.
It provides a stable, consistent way for applications to deal with the hardware witho
ut having to know all
the details of the hardware.
Functions of OS in detail:
OS acts as an interface between hardware and users. It controls overall operations of computers. It is mainly
used for job management, data management, virtual memory management
, input/output management, process
management, security etc.
OS manages the job waiting to be processed. It recognizes the jobs, identifies their
priorities, allocates the memory for the job, schedules and finally runs each job at the appr
Data management keeps track of the data on disk, tape and optical storage
devices. The operating system's file system knows where that data are physically stored.
Virtual Storage Management
OS is used for virtual memory ma
nagement. OS makes possible to
increase the capacity of main memory with out actually increasing its size.
OS manages the input and output operation of computer. This applies to
the flow of data among the different devices of compu
ter and application programs.
The main activities of process management are job queuing, job scheduling,
keeping track of the status of each process etc.
OS job is to secure data inside the memory of computer. O
provide password protection to keep unauthorized users out of the system.
OS acts as an interface between a user of a computer and the computer hardware.
s of Operating System
Easy interaction between human an
Starting computer operation automatically.
Loading and scheduling users’ programs/processes.
Controlling I/O devices
Managing various types of memories such as primary, secondary, cache etc.
Providing security to users’ jobs and files.
ng hardware resources and handling network communication.
Allowing users to share data and software among themselves.
Preventing the system from unauthorized user, programs etc.
Types of Operating System
Within the broad family of operating systems, there
are generally four types, categorized based on the types of
computers they control and the sort of applications they support. The categories are:
user, single task Operating System
As the name implies, this operating system is designed to manage t
he computer so that one user can
effectively do one thing at a time. The MS
DOS etc are single user OS.
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user, multi tasking Operating System
This operating system allows a computer to perform more than one task at a time. Microsoft's Win
and Apple's Mac OS (Leopard) platforms are both examples of operating systems that will let a single
user have several programs in operation at the same time.
user Operating System
user operating system allows many different users to ta
ke advantage of the computer's resources
simultaneously. UNIX, VMS and mainframe operating systems, such as
, are examples of multi
time Operating System (RTOS)
time operating systems are used to control machinery, sc
ientific instruments and industrial systems.
Some examples of real time operating systems are BLMX, BSO/RTOS etc.
BLMX = Board
Level Multitasking eXecutive
BSO/RTOS = Boston Systems Office/ Real
time Operating System
Interface is a common b
oundary between the user and the computer system. OS provides two types of User
CUI (Command User Interface)
A CUI (command user interface) is a user interface to a computer's
which the user responds to a visual prompt by typing in a command on a specified line, re
response back from the system, and then enters another command, and so forth. MS
DOS and UNIX are
CUI operating systems.
GUI (Graphical User Interface)
GUI is graphical user interface. It is user friendly and easy to understand and use. A GUI use
to carry out commands such as opening f
iles, deleting files, moving files, etc. and
although many GUI Operating Systems are operated by using a
, the keyboard can also be used by
A few examples of a GUI Operating Systems:
Microsoft Windows 95
Apple Mac OS
A few examples of a GUI interfaces are:
Differentiate between CUI and GUI OS
It is based on graphical user interface mode.
It is based on command user interface mode.
It is graphical and user friendly.
It is more
textual and less user friendly.
It is very common.
It is less common.
It uses keyboard and mouse.
It uses only keyboard.
It consists of different components such as
text box, icon, desktop, pointing device etc.
It does not consist such components.
Some Technical Terms
A buffer is a region of
used to temporarily hold
while it is being moved from one place to
another. Typically, the data is stored in a buffer as it is retrieved from an
(such as a keyboard)
ust before it is sent to an output device (such as a printer). However, a buffer may be used when
moving data between
within a computer. So, buffering i
s a process of placing the data in a
buffer in order to increase the processing capability of a device.
, spooling refers to a process of transferring data by placing it in a temporary working
area where another program may access it for processing at a later point in time. The term 'spool' is an
acronym of 'Simultaneous Peripheral Operations On
This temporary working area could be a
, but probably not a
By using a process spooling, multiple users can send jobs to a printer simultaneously. When
users send documents (known as print jobs) to a networked printer, each job is store
d temporarily on the
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file server. As the printer finishes printing the current job, the file server sends the next job to the printer
so that it can be printed).
Virtual memory is the use of secondary storage devices as an extension of the
primary storage of the
computer, thus giving the appearance of a larger main memory than actually exists.
system, each process is divided into a number of fixed length blocks called 'pages',
typically 4K bytes in length. Memory space is v
iewed as a series of 'page
frames' of the same
size. When a process is to be executed, only the pages that are immediately required are loaded
In a virtual memory system, Swapping is a technique in which high priority process is swa
main memory and low priority process from main memory is swap out. When high priority
process is completed, low priority process is swap in again.
It is a form of processing in which a computer holds more than one program in memory
and works on
them in round
robin fashion that is, by sharing out the processor's time so that each program receives
some attention some of the time. This way of working is in contrast to using the processor to run one
program at a time.
tasking, in an
, is allowing a user to perform more than one computer
the operation of an
) at a time. Microsoft
are examples of operating systems that can do multitasking (almost all of today's operating systems can).
When you open your Web
and then open
at the same time, you are causing the operating
system to do multitasking.
threading is the ability of an
different parts of a
must carefully design the program in such a way that all the
at the same time without interfering with e
assigns priority to jobs but also admits new jobs for processing at appropriate
times. When a user job is submitted, the system takes note of its time of arrival, processing requirement
etc. Considering al
l these factors, the scheduling
chosen. There are two types of scheduling
preemptive scheduling, a scheduled job always completes before
another scheduling decision is made.
tive scheduling, a scheduling decision can be made even while the
job is executing.
Some scheduling algorithms are:
FCFS (First Come, First Serve
SJF (Shortest Job First)
Round Robin Scheduling
Multilevel Feedback Queue
An interrupt is a signal g
enerated by an event that alters the sequence in which a processor executes
instructions. To handle interrupt Operating System has one special routine called ISR (Interrupt Service
A signal created and sent to the CPU that is
caused by some action taken by a
hardware device is called hardware interrupt. For example, keystroke depressions and mouse movements
cause hardware interrupts.
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A software interrupt, also called an exception, is an interrupt that is cau
, usually by a
. Examples of events that cause them are requests by
for certain services from the operating system or the termination of such programs.
Choices of Operating System
Acronym for “Disk Operating System”.
DOS is a 16
operating system that does not
tasking. It is far easier to administer than UNIX, but less powerful. Compared to graphical
interfaces such as Windows and Mac OS X, it's also not particularly user
Windows Operating System
The Windows operating system is developed and maintained by Microsoft, the company founded by Bill
Gates. The first version was released in 1985. Since then, it has grown significantly, and it now dominates
uses a graphical user interface to make it easier for people to use their computers.
The primary ways that people
are through icons on the desktop and th
e Start menu.
The Windows operating system, like the
, allows people to manage files and run
software programs on desktop and laptop computers.
ronounced as YOO
niks) is a computer
originally developed in 1969 by a group
. UNIX runs on many types of computers, including supercomputers,
notebook PCs, mainframes and minicomputers. Its main a
bility is that it works with so many kinds of
Linux is a generic term that commonly refers to
that use the
. Linux is one of the most prominent examples of
typically all the underlying
used, freely modified, and redistributed by anyone.
etc are few examples of Linux distributions.
Data processing is any
There are many
types of data processing techniques. Some of them ar
It is also called deferred Processing or off
line processing in which tasks are stored in the form of batches and
processed each batches as requirement. It is a slow process of data processing. The purpose of batches is to
give full co
ntrol over the data as it is easier to handle a batch at a time.
line processing is a fast processing in which input device is directly connected to computer. It is also
called direct access or random access processing. In this
processing result of data processing transaction is
available immediately. E.g. ATM (Automated Teller Machine).
time Processing or Multi
Real time means immediate response from computer. The essential feature is that the input data must be
rocessed quickly enough so that further action can be promptly taken on the result.
Distributed Data Processing
processing system in which processing is
with the computers and storage devices