Download MODULE 5[1]

MODULE 5
A set of instructions to the computer that tells to do some specified task is called a
program. A program is generally complete in it and is used by the author of the program only.
Software is a collection of meaningful programs that can together accomplish a defined
task, along with its documentation. The software in a computer system acts as an interface
between the user and hardware part of the computer. The command to be given to the hardware
to perform the task is given and implemented through the software. A functional block diagram
of the interface may like,
User
Software
Hardware
1. APPLICATION SOFTWARE AND SYSTEM SOFTWARE
Software is the intangible part of the computer system. It acts as an interface between the
user and the hardware in the other extreme. It may be of two types :
the application software and the system software.
Application software is a subclass of computer software that employs the capabilities of
a computer directly and thoroughly to a task that the user wishes to perform. The application
software is the software to serve the needs of the user. It is the computer software designed to
help the user to perform the specified task. Common examples for the application software
includes : Word processor(line MS word), Resource management software(banking software
etc), entertainment software(games) etc.
Word processing (MS- word) : MS- Word is the word processing program which involves
the transformation of written text into a form, that gives it a format. Systematic look that
facilitates easy reading
 A word is a computer based program that
-
Is used to type text
Correct spellings and grammar errors as we type
Allows us to add headers and footers
Allows us to share resources available to all office programs such as
clip arts, drawing tools etc.
System software is computer software designed to operate the computer hardware and to
provide and maintain a platform for running application software. System software serves the
needs of the application software to work. So the system software arranges an environment for
the application software to execute correctly and effectively. It may be considered as an interface
between the application software and the hardware. So the above shown arrangement can be
expanded as :
Application
software
User
System
software
Hardware
Some of the system software are OS, compiler etc.
2. PROGRAMMING LANGUAGES
Programming languages are the medium to communicate between the user and the
system. The communication is done in the form of programs. Programming languages can be
used to create programs that control the behavior of a machine, to express algorithms precisely,
or as a mode of human communication. A programming language is composed of a group of
valid words usually called keywords which are having a specific meaning, and the grammar
which specifies the right usages of the keywords. The instructions in a language are created using
the right combination of these keywords. Any violation in the use of the keywords and the
grammar in the program is an error. The set of valid instructions in a programming language is
known as the instruction set. It will be different for different languages. When writing the
program we should strictly follow the instruction set of the language used. The person who is
building the program is the programmer.
Instructions to the computer are given with the help of computer languages. These
languages can be classified as follows
o Machine languages
o Assembly language
o High level language
Machine languages

It is the programming language in which the instruction set includes only 1s and
0s. It is the lowest level programming language. As it contains only 1s and 0s, it
can be directly executed by the computer.

All computer system has its own machine language. The programs are written in
the machine readable format, so its execution is fast. But it is very difficult for the
user to remember the instructions in the binary format. Also it is very difficult to
understand the already written program. So it is rarely used for programming.
o Advantages
 Machine language is faster in execution
 It does not require any translation
 It makes efficient use of storage
 It can be used to manipulate individual bits
o Disadvantages
 Machine language is machine dependent
 It is difficult to understand and develop a program
 There are chances of frequent errors
 It is difficult to correct or modify programs
Assembly language





Assembly language is a low level programming language which implements
symbolic representations of the binary code. It is the next level to the machine
language.
The keywords in the assembly language are implemented in terms of mnemonics.
It is highly machine dependent. It means the mnemonics of one machine may not
be valid for other machine. So the assembly language programs are not portable
between the machines.
The assembly language program that is given to assembler for translation into
machine language is called source program and the translated machine language
program is called the object program.
Writing assembly programs will be easier for the programmer than in the machine
language as it is having mnemonics other than the binary combinations as in
machine language. But the machine can understand only the code in binary format
that is the machine readable format. So to execute the assembly language program
it should be converted into the machine readable format.
Because it is extremely low level, assembly language can be optimized extremely
well. Therefore assembly language is used where the utmost performance is
required for applications. Assembly language is also useful for communicating
with the machine at a hardware level. For this reason, it is often used for writing
device drivers.
Example of mnemonics are:
 ADD – can be used for addition
 MUL – can be used for multiplication
 SUB – can be used for subtraction
o Advantages
 It gives more readability than machine language
 It is easier to understand and use
 It is easy to locate and correct errors
o Disadvantages
 It is machine oriented language
 It is less efficient than machine language
 It needs translator
High level language
 The high level language is the programming language that shows great abstraction
from the details of the computer. The keywords are not specific to any of the
machines. So it is portable. That means the same program can be reused in any
of the machines.
 It uses English like words as keywords that are easier for the programmer to
remember. Also the program will be easy to understand. In writing the high
level program the programmer does not have to worry about the address. The
program written in the high level language must be translated into the machine
readable format.
 Some commonly used high level languages are C, C++, java etc.
o Advantages
 It is machine independent
 It is easy to learn and use
 Errors in programming are less
 Program preparation cost is less
o Disadvantages
 Less efficient
 It is not flexible
 Requires more memory
 Slow in execution
3. LANGUAGE TRANSLATORS
 Language translators are the system software that translates the program written
in one language into other language.
 The user may develop program, in higher level languages as they are easy to
develop and maintain. But a machine cannot understand a program written
using high level language (HLL). These HLL programs are to be converted into
machine language program before a computer can execute the program

For that a special type of the system software is requires to convert HLL
programs into corresponding machine language. They are known as language
translators.

Their action involves two steps: First the input program is checked whether
there is any error. The error means there is any violation in the valid keywords
and the grammar. If there is any error it will produce the corresponding error
message. If there is no error, the code will be converted into the machine
language. The code written by the user is called the source code. It is converted
by the translators to make the object code which can be executed by the
machine.
Source Code
(high level
language
Translators
Object code
(Machine language
program)
program)
The three major types of translators are:
1.
Assembler
2.
Interpreter
3.
Complier
Assembler:

It is the software that converts the assembly code into the machine language. The
process is called the assembly process.
 The user program that is fed as input to the translator is known as source program and
the resultant machine language program is called the object program
Source Program
(Assembly Language)
Assembler
Object Program
(Machine Language)
Interpreter
 Interpreter is system software to translate the higher level program into the machine
code.
 The interpreter is translating the code one by one at the time of execution. Only after
the translation and execution of the first line the interpreter will go to process the 2nd
line.
 Let a program is having an error in the last line. Then only after executing up to the last
line the error will be revealed if in case of interpreter
 Example - BASIC interpreter
Source Program
(high level Language)
Interpreter
Object Program
(Machine Language)
Compiler




Compiler is system software to translate the higher level program into the machine
code.
In case of compiler, it will convert all the lines (means the entire program) into machine
code first and then only the resulting code will start execute from the beginning.
In compiler, the error will be handled before the starting of the execution.
In case of loops the compiler will have to compile it only once.
Source Program
(high level Language)

Complier
Object Program
(Machine Language)
Example - C compiler
Comparison between complier & Interpreter
COMPLIER
INTERPRETER
Scans the entire program first and Translate the program line by line
translates it into machine code
Converts the entire program to Each time the program is executed,
machine code, when all syntax errors every line is checked for syntax errors,
are removed, execution takes place
and then converted into equivalent
machine code
Slow for debugging
Good for fast debugging
Execution time is less
Execution time is more
4. OPERATING SYSTEM

An Operating system is software or a collection of program that controls the execution of
application programs and acts as an interface between hardware and user or applications.
Its objectives are
(i) Convenience
-Makes the computer more convenient to use
(ii) Efficiency
-Allows computer system resources to be used in an efficient manner
Layers of computer system
A computer system can be divided roughly into four components: the hardware, the
operating system and other system programs (utilities), the application programs, and the users.

The primary goal of operating system is convenience for the user. The OS
provides an interface for the user to communicate with the hardware. The user
friendliness of the system is brought to the user by the OS.

One other goal of the OS is to provide efficiency for the computations. The
efficiency is achieved by managing the resources in the optimized manner. It
manages to ensure the availability of the resources for different programs at the
correct time and deallocate the allocated resources for the programs that complete
the use of the resource.

The resources include memory, I/O devices, CPU etc. If more than one program is
running at the same time, all programs will demand the resources for the execution
but the resources are limited. The OS will manage to make all the resources
available to the programs. The OS designed so that it better managed to get the
maximum efficiency. To give efficiency the OS performs





memory management
process management
I/O management
Storage management
Job scheduling
The OS performs the overall control to the system.
Types of operating systems
1) Multiprogrammed system: It is type of OS that support multiple programs running at
the same time in the system.
2) Real time system: A real-time system is used when rigid time requirements have been
placed on the operation of a processor or the flow of data; thus, it is often used as a
control device in a dedicated application.

Air traffic control

Space shuttle

Home appliance

Nuclear power plant
3) Single user operating system : is a type of operating system that is developed and
intended for use on a computer or similar machine that will only have single user at
any given time
4) Multi user system: It is the type of OS that more than one user can use the system at
the same time.
5) Batch processing operating system: here interaction between the user and the
processor is limited or there is no interaction at all during execution of work. Data
and programs that need to be processed are bundled and collected as a batch and
executed together.
5. PROGRAMMING
Programming is the process of creating programs to accomplish a defined task. The
process of programming will be difficult in case of bigger programs. So to make the process
easier, the task may be divided into small pieces and each part is separately solved and after that
it is joined to make the software.
There are two approaches to the programming process : procedure oriented and object
oriented.
Procedure oriented programming (POP):
Here the problem is viewed as a sequence of things to be done such as reading calculating,
printing etc. POP mainly consist of writing a list of instructions and organize these instructions
into functions. The primary focus is on functions. While creating the function a very little
attention is given to the data that are being used by the functions. Most of the functions share the
same data. Data moves around the system from function to function. Emphasis is mainly on
doing things. The data that is shared by functions is vulnerable to abnormal changes. As the data
shared by many functions, if we need to revise the data, we should revise the function that used
the data also. The POP is not model real world situations.
The entire approach revolves around the procedures that need to be created and executed to
accomplish the task. It involves the following steps:
1. Analyze the problem.
2. Determine the objectives (What is to be accomplished?).
3. Identify the steps to be taken.
4. Every step or action needs to be supported by a procedure.
5. The steps are carried out (procedures are called) in a proper sequence to obtain the
desired result.
e.g. you can break down the entire admission process into following subtasks:
1. Accept a new student
2. Validate the student’s documents
3. Record number of subjects opted by the student
4. Check the fee details of the student
5. Maintain the student’s attendance.
Object oriented programming(OOP) : Object-oriented programming (OOP) is a
programming paradigm that uses "objects" -consisting of data fields and methods together with
their interactions – to design applications and computer programs. OOP treat data as a critical
element in the program development and does not allow it to flow freely around the system. It
ties data more closely to the functions and protects it from accidental modifications from outside
function. Here the emphasis is given to data rather than procedure. Here the program is divided
into number of entities called OBJECTS. The object is a cage containing the data and the
functions that is manipulating that data. The wrapping up of data and functions into a single
structure is called the encapsulation. The data in an object can be accessed only by the function
in that object. The data is hidden to the external functions. This process is known as Data hiding.
Thus the accidental modification of the data can be avoided. Also a new object can be derived
from an existing object. So the new object will have the properties of the parent object and the
new object will have its own properties. This method of inheriting the behavior from the parent
by the child is known as inheritance. Thus the same property can be reused.











Points to remember
The problem is visualized and modeled in terms of objects, which is a realistic paradigm
in nature.
The OOP systems can be easily updated and upgraded from the point of view of software
maintenance and development which otherwise would have been cost prohibitive.
The data is the most critical central theme in oop. This enables us to focus on more
details of data which is the most important precious resource.
The data hiding provides more security to data and its maintenance.
The inheritance enables better and optimal organization of data in an hierarchical model.
The program development can concentrate more on message passing between the objects
rather than on the general code.
The OOP paradigm is a modern technology.
Software complexity is reduced
OOP systems can be easily upgraded
One to one relation can be established between the objects in the real world and those in
the program.
It is easier to partition the projects based on objects and interfaces.
OOP has properties which procedural oriented programming doesn’t have.
They are:






Inheritance
Polymorphism
Encapsulation
Class extensibility
Abstract classes
Code reusability
Difference Between Procedure Oriented Programming (POP) & Object Oriented
Programming (OOP)
Procedure Oriented Programming
In POP, program is divided into small
Divided Into
parts called functions.
In POP importance is not given to data
Importance but to functions as well as sequence of
actions to be done.
Approach POP follows Top Down approach.
POP does not have any access
Access
Specifiers specifier.
Data Moving
In POP, Data can move freely from
function to function in the system.
Object Oriented Programming
In OOP, program is divided into parts
called objects.
In OOP, Importance is given to the data
rather than procedures or functions
because it works as a real world.
OOP follows Bottom Up approach.
OOP has access specifiers named Public,
Private, Protected, etc.
In OOP, objects can move and
communicate with each other through
member functions.
OOP provides an easy way to add new
data and function.
In OOP, data cannot move easily from
In POP, Most function uses Global data
function to function, it can be kept public
Data Access for sharing that can be accessed freely
or private so we can control the access of
from function to function in the system.
data.
POP does not have any proper way for OOP provides Data Hiding so provides
Data Hiding
hiding data so it is less secure.
more security.
In OOP, overloading is possible in the
form of Function Overloading and
Overloading In POP, Overloading is not possible.
Operator Overloading.
Examples of POP are: C, VB,
Example of OOP are : C++, JAVA,
Examples
FORTRAN , Pascal.
VB.NET, C#.NET.
Expansion
To add new data and function in POP
is not so easy.
http://www.scribd.com/doc/40401275/RTOS