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Dr. Kajal Rai

• An operating system is a set of computer programs that controls the

computer hardware and acts as an interface with the application

programs.

• The operating system plays a central role in the functioning of a

computer system. It is usually stored on disk, after the computer

system is started or booted up portions of operating system are

transferred to memory as required.

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• The kernel as the name suggests is the heart of the operating

system and controls the most critical processes.

• Windows by Microsoft, Linux, UNIX, and the Macintosh are the

commonly used operating systems.

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• An operating system performs allocation and assignment of system resources, schedules the use of computer resources, monitors the computer system activities etc.

• The various activities performed by a typical operating system are:

• Performing common computer hardware functions.

• Providing a user interface

• Providing a degree of hardware independence

• Managing system memory

• Managing processing tasks

• Providing networking capability

• Controlling access to system resources

• Managing files

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• All application programs must perform certain tasks.

• For example

• Getting input from the keyboard or some other input devices

• Retrieving data from disks

• Storing data on disks

• Displaying information on a monitor or printer

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• Each of these basic functions requires a more detailed set of

instructions to complete.

• The operating system converts a simple, basic instruction into

the set of detailed instructions required by the hardware.

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• In effect, the operating system acts as intermediary between

the application program and the hardware.

• The typical OS performs hundreds of such functions, each of

which is translated into one or more instructions for the

hardware.

• The OS notifies the user if input/output devices need attention,

if an error has occurred, or if anything abnormal has happened

in the system.

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• One of the most important functions of any operating system is providing a user

interface.

• A user interface allows individuals to access and command the computer system.

• The first user interfaces for mainframe and personal computer systems were

command based.

• A command-based user interface requires that text commands be given to the

computer to perform basic activities.

• For example, the command ERASE 00TAXRTN would cause the computer to erase

or delete a file called 00TAXRTN. RENAME and COPY are other examples of

commands used to rename files and copy files from one location to another.

• Many mainframe computers use a commandbased user interface.

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• A graphical user interface (GUI) uses pictures (called icons) and menus displayed on screen to send commands to the computer system.

• Many people find that GUIs are easier to use because user intuitively grasp the functions.

• Today, the most widely used graphical user interface is Windows by Microsoft.

• As the name suggests, Windows is based on the use of a window, or a portion of the display screen dedicated to a specific application.

• The screen can display several windows at once.

• The use of GUIs has contributed greatly to the increased use of computers because users no longer need to know command-line syntax to accomplish tasks

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• A programming language is a computer language programmers

use to develop applications, scripts, or other set of instructions

for a computer to execute.

• Programming languages such as C, C#, Java, Visual Basic are

used to develop applications; AIML, Prolog, C, C++ are used

for artificial intelligence development, Dbase, FoxPro, MyJSql,

Sql etc. are used for database development;

• Assembly language, C are used to develop computer device

drivers or other hardware interface development;

• HTML, Java, JavaScript, Perl, PHP, XML are used for internet

and web page development and so on.

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• There are 2 types of computer languages:

• Low level language and

• High level language.

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• Machine language and assembly language are called low level

language because they are used to write programs that deal

with the low level tasks such as transferring data from memory

to disk, or rendering text onto a display.

• Low level language is machine dependent i.e. a program

written for one type of computer does not work on other

computers.

• You need to know the details of a computer rather than

problem for which you are writing programs.

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• The lowest-level programming language. Machine languages are the only languages understood by computers.

• While easily understood by computers, machine languages are almost impossible for humans to use because they consist entirely of numbers.

• It is tiresome and error prone to program in machine language.

• Programmers, therefore, use either a high-level programming language or an assembly language.

• Every CPU has its own unique machine language. Because machine language is directly understood by computer you don’t need to convert it to run.

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• Assembly languages are between machine languages and high-level

languages. Assembly languages are similar to machine languages,

but they are much easier to program in because they allow a

programmer to substitute names for numbers. Machine languages

consist of numbers only.

• So, assembly language is a much more readable rendition of

machine language. It uses mnemonic codes to refer to machine code

instructions, rather than using the instructions’ numeric values directly.

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• Assembly language is the most basic programming language

available for any processor. With assembly language, a

programmer works only with operations implemented directly

on the physical CPU. Assembly language lacks high-level

conveniences such as variables and functions, and it is not

portable between various families of processors.

• Though assembly language is very close to machine language,

computer can’t execute it directly. The language translator that

can create machine codes out of assembly language is

called Assembler.

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• High level language is a machine-independent programming

language, such as C, C++, Java, Perl and COBOL. It lets the

programmer concentrate on the logic of the problem to be solved

rather than the intricacies of the machine architecture such as is

required with low-level assembly languages.

• High level languages uses English like statements and mathematical

notations. Because a programmer now does not need to remember

the machine architecture and operations implemented directly on

the physical CPU, high level languages are machine independent.

They are often called problem oriented languages or business

oriented language.

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• High level languages were developed towards the end of

second generation of computers (COBOL and FORTRAN) and

flourished during third and fourth generations. Pascal, C, C++,

C#, LISP, Java, Basic etc. are the examples of high level

language.

• High level language is completely different than what machines

can understand. To run a program written in high level

language, you need to convert it into machine code. There are

two kinds of language processors to convert high level

language into machine language – interpreter and compiler.

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• Utility software is system software designed to help analyze,

configure, optimize or maintain a computer. Utility or a tool is

the term used for a single piece of utility software. Utility

software are also referred to as service program, tool, service

routine, or utility routine.

• Utility software usually focuses on how the computer

infrastructure (including the computer hardware, operating

system, application software, and data storage) operates.

Utility software is often targeted at technical people with an

advanced level of computer knowledge.

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• You can find utilities in different categories, such as:

• Anti-virus utilities scan for computer viruses.

• Backup utilities can make a copy of all information stored on a disk, and restore either the entire disk (e.g. in an event of disk failure) or selected files (e.g. in an event of accidental deletion).

• Data compression utilities output a shorter stream or a smaller file when provided with a stream or file.

• Disk checkers can scan operating hard drive. Disk cleaners can find files that are unnecessary to computer operation, or take up considerable amounts of space. Disk cleaner helps the user to decide what to delete when their hard disk is full.

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• Disk compression utilities can transparently compress/uncompress

the contents of a disk, increasing the capacity of the disk.

• Disk defragmenters can detect computer files whose contents

are broken across several locations on the hard disk, and move

the fragments to one location to increase efficiency.

• Disk partitions can divide an individual drive into multiple logical

drives, each with its own file system which can be mounted by

the operating system and treated as an individual drive.

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