OPERATING SYSTEM

 It is the first layer of software loaded into computer memory when it starts up. As the
first software layer, all other software that gets loaded after it depends on it for various common
core services. These common core services include disk access, memory management, takes
scheduling, and user interfacing. In addition the operating system ensures that different
programs executing at the same time do not interfere with each other. It provides a software
platform on top of which other programs can run. In simple words, the operating system
organizes and controls the hardware. Examples of operating systems are Windows XP, UNIX,
and Linux.

OPERATING SYSTEM
The operating system is a software program that acts as an interface between the user and
the computer. It is used to control and manage the hardware components such as keyboard,
monitor, printer, scanner etc.

FUNCTIONS OF AN OPERATING SYSTEM

a) Process Management:
It handles the creation, deletion, suspension, resumption, and synchronization of process.
b) Memory Management:
It handles allocation and de-allocation of memory space as required by various programs.
c) File Management:
It is responsible for creation and deletion of files and directories. It also organizes, stores,
retrieves, names, and protects all the files.
d) Device Management:
It manages all the devices of the computer system such as printers and modems. If any
device fails, it detects the device failure and notifies the same to the user.
e) Security Management:
Protects system resources and information against destruction and unauthorized use.
f) User interface:
Provides the interface between the user and the hardware.

DOS (Disk Operating System)

MS-DOS was the widely used operating system before the introduction of the Windows
operating system. Even now the MS-DOS commands are used for carrying out many jobs like
copying the files, deleting the files etc. The DOS is a set of computer programs. The main
functions of DOS are to manage files, allocate system resources according to the requirement. It
provides essential features to control hardware devices such a keyboard, screen, disk drives,
printers, modems etc. Thus, DOS is a medium through which the user and external devices
attached to the system communicate the command with the system. DOS translate
communication issued by the computer in the format that is understandable by the computer and
instruct computer to work accordingly. It is also translates the result and any error message in the
format for the user to understand.

DOS Commands

We can type all DOS commands in either upper or lower case letters. There are two basic
types of DOS commands:

Internal commands

These commands, like COPY, DEL, and TYPE, are stored in computers memory. Many
DOS commands fall into this category.

External commands

This group of commands is stored on the disk. To use them, either insert the DOS floppy
disk, or change to the directory on hard disk which contains DOS external commands. Examples
of external commands include FORMAT, DISKCOPY, and CHKDSK.
Some commands can take several forms. These separate forms are used by including
various parameters with the command. Parameters, which will be discussed with each command,
are indicate by a / mark. Here is an example of command with an attached parameter:
C:\>DIR/W
[DOS command DIR is attached with parameter W]
All DOS commands must be activated by pressing the <Enter> key after typing the
command.

Features of DOS

• Single user system
• Machine independence
• Program control
• Peripheral management
• Operating with Directories
• Managing files
• Processing commands
• Managing input and output
• Data securing
• Using Batch files
• Managing memory
• Setting up environment
• Command processing - DOS shell(a set of commands which is used to create the programs)
• Operating with Assembler.

Advantages of DOS

The DOS provides the following advantages:

• Machine independence
• More security
• User friendly environment
• More useful in commercial applications.
• Error finding and recovery is more efficient
• Facilities more graphical user interfaces.
• Easy debugging

WINDOWS OPERATING SYSTEM

Microsoft Windows is the most popular operating system around the world. Even those
who are new to computers can use it with a little practice. With the help of Windows, we can
operate the computer just by clicking the mouse buttons, Windows95, Windows98, Windows
2000 and Windows XP are the various versions of Windows.
Windows is an operating system. It is the extension of the disk operating system.
Windows is system software. It requires DOS to run the application programs. The DOS should
be loaded into the memory before the window is executed. After the windows is loaded into the
memory the windows environment takes all the device controls. It also takes care of the memory
management of the programs run by the windows software".

Types of windows

There are two types of windows. They are
(a) Application windows - displays the executable program in graphical user interface mode.
(b) Document window - generated by executable or application program.

Features of Windows

The important features of Windows 98 are as follows:
(a) Graphical User Interface
Windows 98 provides user-friendlier interface to work on. Its improved graphical user interface makes learning and using windows 98 more natural and easier for all types of users. It is more powerful, customizable and efficient.
 (b) Type of icons (Small Pictures):
There are three types of icons. They are
i) Applications icons - the minimized version of the currently running application programs. It appears at the bottom of the desktop and can be maximized.
ii) Document icons - the reduced document windows.
iii) Program icons - appear with in program manager and clicking on these icons activate the associated applications and also load the related documents or files.
(c) Start Button
Introduction of START button by windows 98 made life much simpler while there is a need to access multiple programs. It is the gateway of accessing most of the functionality available in the computer loaded with windows 98. Just Click on the start button anytime to start any programs, open or find documents, change windows settings, get Help, manage Files, maintain System, much more.
(d) Taskbar
The Task bar provides information and access to the entire task that has been currently activated by windows 98. Using this one can keep a track of what all programs have been activated and switched between them.
(e) Windows Explorer
Windows Explorer more or less acts as File Manager for windows 98, but with lots of new features. It is more efficient, faster and user friendly. Using Explorer one can easily browse through all the drives and network resources available and manage files.
(f) Right Mouse Button
Clicking on the right mouse button activates a pop-up menu in any program so as to help in completing a task efficiently.
(g) Long File Names
As the MS-DOS convention follows, none-of the file used in DOS environment should be more than 8 character of primary name and optimal secondary name (extension) of three characters. However Windows 98 has broken this barrier. Windows 98 supports long file names maximum of 225 characters. It also allowed space to be used in between file name. This helps to make files and folders (directory/subdirectory) easier to organize and find.
h) Shortcuts
As the name suggests, SHORTCUTS are the shortest way to access programs, files other resources in Windows 98. Instead of going through the structural process of accessing a program, one can create “shortcuts” to access them. It creates links for easy access to file, programs, folders and more.
i) Multitasking
Multitasking allows the user to activate and accomplish more than one task at a time. For example, work on a document file WORD programs, which copies file from other computer available in time on the network. With Windows 98, 32 - bit computing environment, the user can do more than one task a time.
j) Easy Internet Access
Integration of Internet Explorer 4.0 and Active Desktop, which coupled the Internet html hypertext links more tightly to the Windows 98 user interface.
k) Software Compatibility
Windows 98 provides complete backward compatibility. It is easily compatible with other applications developed for MS-DOS and Windows 3.x environment. It also supports latest 32-bit technology. Most of the latest software packages are now built on Windows 98, operating environment.
l) Great Gaming Platform
Windows 98 supports rich graphics, high quality audio and video. Software to take advantage of Intel's Multimedia Extensions (MMX) to the IA - 32 instruction set, which are designed to improve the performance of multimedia applications and games developed for windows 98 that uses MMX technology.
m) Hardware Compatibility
Windows 98 provides greater Hardware compatibility as compared to any other operating environment. It has flexibility of supporting hardware from different vendors.
n) Find utility
Find Utility of windows 98 allows the user to do searches by partial name, last modified date, or full text. In addition we can save, rename or view files from within the result pane.
(o) Help
Windows 98 provides online help to accomplish a task. If the user is not sure how to perform a task, windows 98 Help will provide structured process how to accomplish the task. Simply right-click on any object in the user interface (icon) and he can get relevant description about that object.
(p) Manage more numbers of PC's
Windows 98 can manage up to eight monitors on a- single PC. The user can drag and drop resize and move desktop items such as windows, folders, icons, and applications, from one monitor to the next.
(q) Additional facilities
Windows 98 includes additional enhancement of Windows 95 that includes new backup
utilities and disk defragmenter capabilities.

Windows NT workstation

Windows NT is a single user; multitasking operating system designed to run on PC workstations and ncorporates all latest developments in operating system technology. It was introduced in 1993. It includes the following:

(a) Windows NT workstation
(b) Windows NT server, and
(c) Windows NT enterprise edition

Features of windows NT server

a) Single User Multitasking
The main feature is that even through it is meant for a single user environment, provides
multitasking. For e.g., a user may use a word processor, a drawing program, a spreadsheet
application to produce a document. Without multitasking, simultaneous use of this will not be
possible. They must process with the s/w one by one; provide alignment making changes will be
a tedious process. In a multitasking environment, the user may keep all the applications open,
prepare the documentation and make necessary change. All of these are possible with increased
speed and memory capacity of microprocessors together with the support for virtual memory.
b) Ability to support all applications
The power of Windows NT comes form its ability to support applications written for
other operating systems. This ability is provided through protected subsystems. The protected
subsystems are those parts of NT that interact with the end user.
c) Client server computing model
The way in which the executive, the protected subsystems, and the applications structured
in NT is by using the client/ server computing model, each server implemented as one or more
process. Such process waits for a request from a client for of its services, eg. memory services. A
client, which may be an applications program or another operating system module, requests a
service by sending a message. The message routed through the executive to the appropriate
server. The server performs the operation and returns the results or status information by means
of another message, which is routed through the executive back to the client.
Client/server architecture has the following advantages:
(i) It simplifies the base operating system, the NT executive
(ii) It improves reliability. Each server runs on a separate process with its partition of
memory, protected from other servers. Also, the servers cannot directly access hardware
or modify memory in which the executive the rest, the operating system.
(iii) It provides a natural base for distributed computing.
d) Support for Threads
An important feature of Windows NT is its support for threads within process. A thread is
a dispatchable unit of work. It is executed sequentially and may be interrupted so that the
processor can turn to other threads. A process is a collection of one or more areas and associated
system resources. This is similar to a program in execution. By checking an application into
multiple threads, the modularity and the timing of application related events could be
maintained.
e) Support of Symmetric Multiprocessing (SMP)
In a multiprocessor system, to achieve maximum efficiency and reliability a mode of
operation known as symmetric multiprocessing (SMP) is desirable. With SMP, any process or
Thread can be assigned to any processor.

f) Windows NT uses concepts of object oriented design
Windows NT uses some concepts of object oriented design. This approach facilitates the
sharing of resources and data among processes and the protection of resources and data among
processes and the protection of resources from unauthorized access.

Advantages of Windows NT

a) It simplifies the base operating system
b) It improves reliability
c) It provides a natural base of distributed computing
d) Operating-system routines can run on any available processor and different routines can be
executed simultaneously on different processors.
e) NT supports the use of multiple threads of execution within a single process.
f) NT processes convenient mechanisms for sharing data and resources between processes.
g) NT provides flexible inter process communication capabilities.
g) Functionality-NT can communicate with many different types of computers.

THE UNIX OPERATING SYSTEM

Like DOS and windows, there’s another operating system called UNIX. It arrived earlier
then the other two, and stayed back like enough to give us the internet. UNIX is a giant operating
system and is way ahead of them in sheer power. It has practically everything an operating
system should have, and several features which other operating systems never had. Its richness
and elegance go beyond the commands and tolls that constitute it, while simplicity permeates the
entire system. It runs on practically every hardware and provided motivation to the open source
movement.
However, UNIX also makes many demands of the user. In requires a different type of
commitment to understand the subject, even when the user is an experienced computer
professional. It introduces certain concepts not known to the computing community before, and
user numerous symbols whose meaning is anything but clear. It achieves unusual tasks with a
few keystrokes, but it takes time to devices a sequence of them for a specific task. Often, it
doesn’t tell you whether you are right or wrong, and doesn’t warn you of the consequences of
your actions. That is probably the reason why many people still prefer to stay away from UNIX.

Features of UNIX

UNIX is an operating system, so it is has all the features an operating system is expected
to have. However UNIX also looks at a few things differently and possesses features unique to it.
The following section gives a clear idea of the major features of this operating system.
a) UNIX: A Multi user System
From the fundamental point of view, UNIX is a multiprogramming system; it permits
multiple programs to run. This can happen in two ways

1. Multiple users can run separate jobs
2. A single user can also run multiple jobs.

b) UNIX: A Multi tasking System Too
A single user can also run multiple tasks at the same time as UNIX is a multitasking
system. It is usual for a user to edit a file, print another one on printer, send email to a friend and
browse the Word Wide Web - all without leaving any of the application. This kernel is designed
to handle a user’s multiple needs.
c) The UNIX Toolkit
By one definition, UNIX represents the kernel, but the kernel by itself doesn’t do much
that can benefit the user. To properly exploit the power of UNIX, you need to use the host of
applications that are shipped with every UNIX system. These applications are quite varied in
scope. There are general – purpose tools, text manipulation utilities (called filters), compilers and
interpreters, networked applications and system administration tools.
d) Pattern Matching
UNIX features very sophisticated pattern matching features. UNIX features elaborate
pattern matching schemes that use several characters from the Meta character set. The matching
isn’t confined to filenames only. Some of the most advanced and useful tools also use a special
expression called a regular expression that is framed with characters from the set.
e) Programming Facility
The UNIX shell is also a programming language; it was designed for a programmer, not a
casual end user. It has all the necessary ingredients, like control structures, loops and variables,
that establish it as a powerful programming language in its own right.
f) Documentation
UNIX documentation is no longer the sore point it once was. Even though it is sometimes
uneven at most times the treatment is quite. The principal online help facility available is the
man command, which remains the most important reference for commands and their
configuration files. Thanks to O’Reilly & Associates, one can safely say that there’s no feature
of UNIX on which a separate textbook is not available.

Apart from the online documentation, there’s a vast ocean of UNIX resources available
on the internet. There are several newsgroups on UNIX where you can fire your queries in case
you are stuck with a problem – be it a problem related to shell programming or a network
configuration issue. The FAQ (Frequently Asked Questions) a document that addresses common
problems is also widely available on the Net. Then there are numerous articles published in
magazines and journals and lecture notes available by universities on their Web sites. UNIX is
easily tamed Operating System.