3.1 Introduction
If you want to get something done by a persons, you will tell him what to do in
a language that he understands. Similarly, if you want to get some work done by
the computer, you have to tell the computer in a language that the computer
understands, i.e., machine language. The machine language consists of only binary
digits, i.e. 0 and 1. It was felt quite difficult and tedious for human beings to
thinks in binary numbers. For communicating with the computer, it was thought
that it is advisable to develop a third language, a programming language, that can
be understood by both human beings and the computer. Thus a programming
language is a set of rules that provides a way of instructing the computer to
perform certain operations.
Programming languages are said to be lower or higher, depending on whether
they are closer to the language the computer itself uses (lower, which means 0s
and 1s) or to the language that people use (higher, which means more English
like).
3.2 Objectives
After going through this lesson you will be in a position to:
l identify various levels (or generations) of language such as machine
language, assembly language, high-level language
l explain the concept of software
2 distinguish between system software and application software
3 distinguish between compiler and interpreter
4 define operating system and its various functions
3.3 Computer Language
The languages in which programs are written are called programming languages.
These languages can be classified into following categories.
l Machine language
l Assembly language
l High level language
Machine Languages
We think of computers as being quite complicated, but actually their basis is
very simple. It is based on the concept of electricity being turned "on" and "off".
From this on/off, yes/no, two-stage system, sophisticated ways of representing
data have been constructed using the binary system of numbers. The binary
system is based on two digits 0 and 1.
By contrast, the decimal system that we all use is based on ten digits 0 through
9. The numbers 1, 2 and 3 in the decimal system are represented in the binary
system as 1, 10 and 11 respectively. Letters of the alphabet are also represented
in binary numbers. In one system, the letter A is represented as 1000001.
Commas, semicolons and other special characters are also represented as
bunches of 0s and 1s.
In the early days of computers, with machines as the ENIAC, which uses vacuum
tubes, one could actually see the tubes lit up or unlit, corresponding to the 1/0
binary state— the switch was either on or off.
In addition, in those early days there was no such things as software. There was
only hardware with electrical on/off switches. Whenever a program was to be
Computer Language/Software :: 39
run, all the switches had to be set - sometimes as many as 6,000 switches for a
single program. Then for the next program, the switches had to be reset, a process
that might take weeks.
Since those days, machine switches have been replaced by machine programming,
programs with statements consisting of 0s and 1s that electrically set the switches,
with 0 representing off and 1 responding on. This has made changing from one
program to another considerably easier.
Still, programming directly in machine language - the lowest level of
programming language, in which instruction is represented as 0s and 1s - is very
tedious and time consuming. A programmer must keep track of a tremendous
amount of detail. Moreover, he/she must understand the technical operations
of the computer. For example, consider a hypothetical line from a program
segment, which multiplies two numbers.
11110010 01110011 11010010 00010000 01110000 00101011
Clearly, working with this kind of code is not for everybody.
Programming in machine code has one advantage over programming at other
language levels - its execution is very fast and efficient because the computer
can accept the machine code as it is. However, in addition to the complexity
involved in working at this level, there is a severe disadvantage to machine
language - there is no one standard machine language. Machine language differs
from machine to machine.
The languages are machine-dependent, and the programs written in machine
language for one computer model will not, in all likelihood, run on a computer
of different model. Although many programs or subroutines in machine language
for a particular computer is supplied by the manufacturer, still few applications
programs are written by users in machine language.
Assembly Languages
From the above discussion it was felt that working with 0s and 1s could turn
people themselves into ciphers. In the 1950s, to reduce programming
complexity and provide some standardization, assembly languages were
developed. Assembly languages, also known as symbolic languages use
abbreviations or memonic code - codes more easily memorized to replace the
0s and 1s of machine languages.
The hypothetical machine language segment we saw above is as follows:
11110010 01110011 11010010 00010000 01110000 00101011
This could be expressed in assembly language statement as :
PACK 210 (8, 13), 02B (4,7)
Actually, assembly languages do not replace machine languages. In fact, for an
assembly language program to be executed, it must be converted to machine code.
The assembly language program is referred to as a 'source program' whereas,
the machine language program is an 'object program'.
Assembly language code is very similar in form to machine language code. In
fact, assembly languages had a one-to-one correspondence which means that 15
assembly statements, would be translated into 15 machine language statements.
This one-to-one correspondence was still laborious. However, assembly
language instructions (called macro instructions) were devised, which executed
batches of one-to-one instructions.
Assembly languages offer several advantages:
l They are more standardized and easier to use than machine languages.
l They operate very efficiently, although not as efficient as the machine
languages.
l They are easier to debug.
However, there are still some disadvantages:
l Assembly language programs are usually very long and difficult to debug.
l Though less abstract than machine languages, assembly language programs
are still complex.
l Though more standardized than machine languages, assembly languages
are still machine dependent.
High Level Languages
High Level Languages helped programmers by reducing further the number of
computer operations details they had to specify, so that they could concentrate
more on the logic needed to solve the problem.
The following example gives you a code segment in which the same instruction
- " Calculate gross pay" - is expressed in three different languages: machine,
assembly and COBOL.
Machine Language:
11110010 011100011 1101 001000010000 0111 000000101011
11110010 011100011 1101 000100001000 0111 000000101111
11111100 01010010 1101 001000010010 1101 001000011101
11110000 01000101 1101 001000010011 0000 000000111110
11110011 01000011 0111 000001010000 1101 001000010100
10010110 11110000 0111 000001010100
Assembly Language
PACK 210 (8, 13), 02B (4,7)
PACK 218 (8, 13), 02F (4,7)
MP 212 (G, 13), 21D (3, 13)
SRP 213 (5, 13), 03E (0), 5
UNPK 050 (5, 7), 214 (4, 13)
IO 054 (7), X ‘FO’
COBOL
MULTIPLY HOURS -WORKED BY PAY-RATE
GIVING GROSS -PAY ROUNDED
3.4 Type of High-Level Languages
Languages are often referred to as generations, the idea being that machine
languages were the first generation and assembly languages were the second
generation. High-level languages are sometimes used to refer all languages
above the assembly level. Here we will subdivide high-level languages into three
generation.
l Procedural-oriented or third generation
l Problem-oriented or fourth generation
l Natural or fifth generation
Procedural-oriented Languages
High-level languages are often classified according to whether they solve general
problems or specific problems. General-purpose programming languages are
called procedural languages or third generation languages. They are languages
such as Pascal, BASIC, COBOL, and FORTRAN, which are designed to express
the logic, the procedure, of a problem. Because of their flexibility, procedural
languages are able to solve a variety of problems.
Procedural languages have many advantages over machine and assembly
languages:
l The program statements resemble English and hence are easier to work
with.
l Because of their English-like nature, less time is required to develop a
program for a given problem.
l Once coded, programs are easier to understand and modify.
l The procedural languages are machine-independent.
However, procedure-oriented languages still have some disadvantages compared
to machine and assembly languages:
l Programs are executed more slowly.
l The languages use computer resources less efficiently.
Problem-oriented Languages and Application Generators
Third-generation languages, such as BASIC or Pascal, require you to instruct
the computer in step-by-step fashion. Fourth-generation languages, also known
as problem-oriented languages, are high-level languages designed to solve
specific problems or develop specific applications by enabling you to describe
what you want rather than step-by-step procedures for getting there.
Fourth- generation languages may be categorized into several kinds of
application development tools:
l Personal computer applications software
l Query languages and report generators
l Decision support systems and financial planning languages.
l Application generators
Personal Computer applications software
You may be knowing about various application softwares for PCs, but the ones
we are particularly concerned with here are word processors, spreadsheets,
database management, business graphics and integrated packages. Knowledge
of spread sheet, Foxpro or Power Point can help you develop your own
applications.
Query languages and report generators
Query languages allow people who are not programmers to search a database using
certain selection commands. Query languages, for example, are used by airline
or railway reservation personnel needing ticket information. Report generators
are designed for people needing to prepare reports easily and quickly. Examples
of query languages and report generators include QBE, SQL, RPG, etc.
Decision support systems and financial planning languages
Decision support systems are interactive software designed to help managers
make decisions. Financial planning languages are particular kinds of decision
support systems that are employed for mathematical, statistical and forecasting
modelling. Both types of languages find applications in developing complicated
business model hypothetical representations of management problems.
Application generators
An application generator consists of a software system with number of program
modules, preprogrammed for various functions, so that the programmer or user
can simply state which function is needed for a particular application, and the
system will select the appropriate module and run a program to meet the user's
needs.
Table 3.1 summarizes some of the major difference between third-generation
languages (3GLs) and fourth-generation languages (4GLs.).
Table 3.1
Difference between 3 GLs and 4 GLs
Third-generation Languages Fourth-generation Languages
Intended for use by professional May be used by a non-programming
programmers. personnel as well as a professional
programmer.
Requires specification of how to Requires specification of what task is
perform task. to be performed (system determines
how to perform the task).
All alternatives must be specified. Default alternatives are built in; an end
user need not specify these alternatives
Require large number of procedural Require fewer instructions.
instructions.
Code may be difficult to read, Code is easy to understand and
understand and maintain. maintain because of English-like
commands.
Language developed for batch Language developed primarily for
operations. on-line use.
Can be difficult to learn. Easy to learn.
Difficult to debug. Easy to debug.
Typically file-oriented. Typically database-oriented.
Natural Languages
Natural languages are still in the developmental stages, but they promise to have
profound effect, particularly in the areas of artificial intelligence and export
systems. Natural languages have two characteristics:
l They are designed to make the connections that humans have with
computers more natural - more humanlike.
l They are designed to allow the computer to become "smarter" - to actually
simulate the learning process by remembering and improving upon earlier
information.
Two popular natural languages are LISP and PROLOG.
3.5 Compilers and Interpreters
For a high-level language to work on the computer it must be translated into
machine language. There are two kinds of translators - compilers and
interpreters. High-level languages are called either compiled languages or
interpreted languages.
In a compiled language, a translation program is run to convert the high-level
language program, which is called the source code, into a machine language code.
This translation process is called compilation.
The machine language code is called the object code and can be saved and either
run (executed) immediately or later. Some of the most widely used compiled
languages are COBOL, C, C ++, FORTRAN, etc.
In an interpreted language, a translation program converts each program
statement into machine code just before the program statement is to be executed.
Translation and execution occur immediately, one after another, one statement
at a time.
Unlike the compiled language, no object code is stored and there is no
compilation. The most frequently used interpreted language is BASIC.
Compiled languages are better than interpreted languages as they can be executed
faster and more efficiently once the object code has been obtained. On the other
hand, interpreted languages do not need to create object code and so are usually
easier to develop and test.
3.6 What is Software
As we know what computer is a machine which cannot do anything without
instructions from the user. In order to do any specific job you have to give a
sequence of instructions to the computer. This set of instructions in a proper
sequence is called a computer program. Software refers to the set of computer
programs that cause the hardware (computer system) to function in the desired
manner. Hardware means physical components of the computer system. We
can say that hardware which cannot perform any calculation, comparison or
manipulation without being instructed to do so. These instructions play a vital
role in the performance of a computer. A complete set of instructions written
to solve a problem on a computer is called software.
3.7 Types of Software
Computer software is normally classified into two broad categories:
(i) System Software
(ii) Application Software
3.7.1 System Software
System software includes general programs written for a computer. It consists
of pre-written programs and documentation supplied by the manufacturer along
with the computer. These programs are held permanently in the machine. The
primary objectives of this software are to:
(i) enhance the efficiency of hardware utilization, and
(ii) make computers simple to use.
The first objective is realized by that component of system software which is
commonly known as operating system.
System Software is a set of instruction to the machine to interpret and execute
application software, for example, language translators (called compilers and
interpreters), operating systems, utilities and special purpose software.
Language Translator
A language translator is a system software which translates a computer program
written by a user into a machine understandable form.
The most elemental form of programming uses only the binary digits 0 and 1,
which is directly understood by the electronic circuits. A program that have only
binary digits is called a machine language program. It is difficult to write or
understand machine language programs, as these consist of 0s and 1s.
Assembly language provides a significant improvement over machine language,
Assembly language programs are written using memonic codes like ADD,
STORE, etc., rather than their machine language representations in binary digits.
Therefore, programming in assembly language is easier. For its execution, it
needs to be translated into machine language code. This translation is done by
an assembler. Both machine language and assembly language programs are
machine dependant.
A program written in a high level language needs to be translated into machine
language code before execution. This translation is done either through a
complier or through an interpreter. A compiler is a translator program which
reads an entire program written in a high level language and converts it into
machine language code.
An interpreter on the other hand, is a translator which converts one statement of
the program into machine code, execute it and then goes on to perform the same
for the next statement, and it continues doing so till the end of the program or
on error occurrence.
Operating System
An operating system is the most important system software and is a must to
operate a computer system. An operating system manages a computer's
resources very effectively, takes care of scheduling multiple jobs for execution
and manages the flow of data and instructions between the input/output units and
the main memory.
The first operating system, called batch processing operating system was
developed for the second generation computers. This operating system executes
jobs serially one after another from a batch of jobs submitted for execution.
The central processing unit is kept busy only during the processing cycle of a
job and remains idle during the input and output operations. A multi programming
opening system handle multiple jobs simultaneously by overlapping the input/
output and processing cycles of various jobs.
Other types of operating system which are popular today are ‘multi-processing
operating systems’ and ‘real time operating systems’. A multi-processing
operating system uses multiple CPUs to process multiple jobs. A real time
operating system is a type of interactive operating system which strict time
limitation. Receiving and processing data is done quickly enough to produce
output, to control, direct or effect the outcome of ongoing activity. The
reservation system used by railway, airlines, hotel are examples of real time
applications.
The function of an operating system can be compared to the functions of a
principal in a school. The principal of the school provides an environment in
which the other employees can do useful work. The principal will do this by
allocating resources available such as allocating time for each period, allocating
classes to teachers and providing rooms for different classes etc. Similarly, an
operating system governs the working of the computer and input/output devices.
The operating system programs act as an interface between the user's programs
and the computer's components and help in the execution of user's programs.
The major functions of an operating system are:
(i) User identification and keeping of the resources used by the users. Thus
un-authorized users cannot use the computer.
(ii) Sharing of computer resources among many users. The sharing is
achieved by permitting simultaneous executions of more than one user
program. This is usually called multi-programming. A mix of programs
can keep the whole memory occupied, all devices active, and the control
unit and ALU constantly busy, thus increasing utilization of hardware.
(iii) Executive batches of programs, one after another, without human
intervention.
(iv) Protection of user's data and programs.
(v) Controlling the transfer of data and programs between the main memory
and secondary storage and other I/O devices.
(vi) Providing programs to select appropriate translators.
(vii) Providing facilities to detect and correct errors in a user's program.
An operating system understands a fixed set of commands. This set of commands
is often called job control language (JCL). The JCL commands are used by the
computer users to indicate their requirements to the operating system. The
operating system which is used with a micro-computer is called CP/M (control
program for microprocessor). Another operating system which is gaining
popularity and which is available on a variety of different machines is UNIX
(UNIX was developed by Bell laboratories). DOS is an operating system
commonly used in PCs.
The second objective of simplifying computer usage is achieved by enabling the
users to write their own programs in languages other than the machine language.
The only language understood by computers is machine language. If any other
language is used, the programs must first be translated into the machine language
before they can be executed. One of the most significant aspect of computers
is that such translations can be made automatically using other programs. A
computer manufacturer provides many programs for the translation of many
languages into the machine language. These programs are called translators or
compliers and form part of the system software.
We rarely talk about computer hardware alone. It is the hardware and software
both which make up a computer system. There is definitely some substance in
the argument that system software is as important, if not more, as its hardware.
Utility Software
Utility software may be considered as a system software which is used quite
often in the development of a program. Sort merge programs are used to sort
records in a particular manner or sequence. Such programs are normally provided
by the manufacturers. The programmer can also develop his own utility software
and keep it in the secondary memory of the computer.
3.7.2 Application Software
Application software is written to perform a specific task or process, such as
accounting, payroll, mailing list, result preparation and so on. The majority of
application software is written in high-level languages.
Assuming that the task to be carried out has been correctly identified, carefully
defined, the prospective user will come across the following alternative sources
for this application software.
(a) Write it yourself : The program written by the user can be the most
satisfactory solution. It will be an exact match to the needs of the
business. The program can grow with the business.
(b) General purpose application packages : Application packages refer
to a set of computer programs, which have been written to perform
specific, commonly required tasks. Each program is written in such a
way that it is applicable to a large number of users. The main advantage
is that it is relatively cheap as cost of the package is spread over a number
of customers. The major disadvantage of application package is that it is
not likely to fulfil all the requirements of the prospective users.
(c) Customer software : It refers to computer programs specially written
to match the exact needs of the user. It is precisely the same as getting
one's clothes stitched from a tailor to fit exactly rather than buying a
ready-made dress. The most important advantage is that such software
fulfils all the needs of the customer. The major disadvantage is that
customer software costs much more than general purpose application
software, because the package is specially made for one particular
customer.
Common Application Packages
Some of the common requirements of the users of personal computers have been
identified and common applications packages have been developed to meet their
needs. These packages include word processor, database processing, spreadsheet
calculations, mail-merge, presentations and communications (email). These
packages have been prepared so that they are simple to use. They also provide
graphical user interface to make them very user friendly. These packages are
readily available in the market and one can purchase them, install it on his/her
computer easily and start using the package.
If you want to get something done by a persons, you will tell him what to do in
a language that he understands. Similarly, if you want to get some work done by
the computer, you have to tell the computer in a language that the computer
understands, i.e., machine language. The machine language consists of only binary
digits, i.e. 0 and 1. It was felt quite difficult and tedious for human beings to
thinks in binary numbers. For communicating with the computer, it was thought
that it is advisable to develop a third language, a programming language, that can
be understood by both human beings and the computer. Thus a programming
language is a set of rules that provides a way of instructing the computer to
perform certain operations.
Programming languages are said to be lower or higher, depending on whether
they are closer to the language the computer itself uses (lower, which means 0s
and 1s) or to the language that people use (higher, which means more English
like).
3.2 Objectives
After going through this lesson you will be in a position to:
l identify various levels (or generations) of language such as machine
language, assembly language, high-level language
l explain the concept of software
2 distinguish between system software and application software
3 distinguish between compiler and interpreter
4 define operating system and its various functions
3.3 Computer Language
The languages in which programs are written are called programming languages.
These languages can be classified into following categories.
l Machine language
l Assembly language
l High level language
Machine Languages
We think of computers as being quite complicated, but actually their basis is
very simple. It is based on the concept of electricity being turned "on" and "off".
From this on/off, yes/no, two-stage system, sophisticated ways of representing
data have been constructed using the binary system of numbers. The binary
system is based on two digits 0 and 1.
By contrast, the decimal system that we all use is based on ten digits 0 through
9. The numbers 1, 2 and 3 in the decimal system are represented in the binary
system as 1, 10 and 11 respectively. Letters of the alphabet are also represented
in binary numbers. In one system, the letter A is represented as 1000001.
Commas, semicolons and other special characters are also represented as
bunches of 0s and 1s.
In the early days of computers, with machines as the ENIAC, which uses vacuum
tubes, one could actually see the tubes lit up or unlit, corresponding to the 1/0
binary state— the switch was either on or off.
In addition, in those early days there was no such things as software. There was
only hardware with electrical on/off switches. Whenever a program was to be
Computer Language/Software :: 39
run, all the switches had to be set - sometimes as many as 6,000 switches for a
single program. Then for the next program, the switches had to be reset, a process
that might take weeks.
Since those days, machine switches have been replaced by machine programming,
programs with statements consisting of 0s and 1s that electrically set the switches,
with 0 representing off and 1 responding on. This has made changing from one
program to another considerably easier.
Still, programming directly in machine language - the lowest level of
programming language, in which instruction is represented as 0s and 1s - is very
tedious and time consuming. A programmer must keep track of a tremendous
amount of detail. Moreover, he/she must understand the technical operations
of the computer. For example, consider a hypothetical line from a program
segment, which multiplies two numbers.
11110010 01110011 11010010 00010000 01110000 00101011
Clearly, working with this kind of code is not for everybody.
Programming in machine code has one advantage over programming at other
language levels - its execution is very fast and efficient because the computer
can accept the machine code as it is. However, in addition to the complexity
involved in working at this level, there is a severe disadvantage to machine
language - there is no one standard machine language. Machine language differs
from machine to machine.
The languages are machine-dependent, and the programs written in machine
language for one computer model will not, in all likelihood, run on a computer
of different model. Although many programs or subroutines in machine language
for a particular computer is supplied by the manufacturer, still few applications
programs are written by users in machine language.
Assembly Languages
From the above discussion it was felt that working with 0s and 1s could turn
people themselves into ciphers. In the 1950s, to reduce programming
complexity and provide some standardization, assembly languages were
developed. Assembly languages, also known as symbolic languages use
abbreviations or memonic code - codes more easily memorized to replace the
0s and 1s of machine languages.
The hypothetical machine language segment we saw above is as follows:
11110010 01110011 11010010 00010000 01110000 00101011
This could be expressed in assembly language statement as :
PACK 210 (8, 13), 02B (4,7)
Actually, assembly languages do not replace machine languages. In fact, for an
assembly language program to be executed, it must be converted to machine code.
The assembly language program is referred to as a 'source program' whereas,
the machine language program is an 'object program'.
Assembly language code is very similar in form to machine language code. In
fact, assembly languages had a one-to-one correspondence which means that 15
assembly statements, would be translated into 15 machine language statements.
This one-to-one correspondence was still laborious. However, assembly
language instructions (called macro instructions) were devised, which executed
batches of one-to-one instructions.
Assembly languages offer several advantages:
l They are more standardized and easier to use than machine languages.
l They operate very efficiently, although not as efficient as the machine
languages.
l They are easier to debug.
However, there are still some disadvantages:
l Assembly language programs are usually very long and difficult to debug.
l Though less abstract than machine languages, assembly language programs
are still complex.
l Though more standardized than machine languages, assembly languages
are still machine dependent.
High Level Languages
High Level Languages helped programmers by reducing further the number of
computer operations details they had to specify, so that they could concentrate
more on the logic needed to solve the problem.
The following example gives you a code segment in which the same instruction
- " Calculate gross pay" - is expressed in three different languages: machine,
assembly and COBOL.
Machine Language:
11110010 011100011 1101 001000010000 0111 000000101011
11110010 011100011 1101 000100001000 0111 000000101111
11111100 01010010 1101 001000010010 1101 001000011101
11110000 01000101 1101 001000010011 0000 000000111110
11110011 01000011 0111 000001010000 1101 001000010100
10010110 11110000 0111 000001010100
Assembly Language
PACK 210 (8, 13), 02B (4,7)
PACK 218 (8, 13), 02F (4,7)
MP 212 (G, 13), 21D (3, 13)
SRP 213 (5, 13), 03E (0), 5
UNPK 050 (5, 7), 214 (4, 13)
IO 054 (7), X ‘FO’
COBOL
MULTIPLY HOURS -WORKED BY PAY-RATE
GIVING GROSS -PAY ROUNDED
3.4 Type of High-Level Languages
Languages are often referred to as generations, the idea being that machine
languages were the first generation and assembly languages were the second
generation. High-level languages are sometimes used to refer all languages
above the assembly level. Here we will subdivide high-level languages into three
generation.
l Procedural-oriented or third generation
l Problem-oriented or fourth generation
l Natural or fifth generation
Procedural-oriented Languages
High-level languages are often classified according to whether they solve general
problems or specific problems. General-purpose programming languages are
called procedural languages or third generation languages. They are languages
such as Pascal, BASIC, COBOL, and FORTRAN, which are designed to express
the logic, the procedure, of a problem. Because of their flexibility, procedural
languages are able to solve a variety of problems.
Procedural languages have many advantages over machine and assembly
languages:
l The program statements resemble English and hence are easier to work
with.
l Because of their English-like nature, less time is required to develop a
program for a given problem.
l Once coded, programs are easier to understand and modify.
l The procedural languages are machine-independent.
However, procedure-oriented languages still have some disadvantages compared
to machine and assembly languages:
l Programs are executed more slowly.
l The languages use computer resources less efficiently.
Problem-oriented Languages and Application Generators
Third-generation languages, such as BASIC or Pascal, require you to instruct
the computer in step-by-step fashion. Fourth-generation languages, also known
as problem-oriented languages, are high-level languages designed to solve
specific problems or develop specific applications by enabling you to describe
what you want rather than step-by-step procedures for getting there.
Fourth- generation languages may be categorized into several kinds of
application development tools:
l Personal computer applications software
l Query languages and report generators
l Decision support systems and financial planning languages.
l Application generators
Personal Computer applications software
You may be knowing about various application softwares for PCs, but the ones
we are particularly concerned with here are word processors, spreadsheets,
database management, business graphics and integrated packages. Knowledge
of spread sheet, Foxpro or Power Point can help you develop your own
applications.
Query languages and report generators
Query languages allow people who are not programmers to search a database using
certain selection commands. Query languages, for example, are used by airline
or railway reservation personnel needing ticket information. Report generators
are designed for people needing to prepare reports easily and quickly. Examples
of query languages and report generators include QBE, SQL, RPG, etc.
Decision support systems and financial planning languages
Decision support systems are interactive software designed to help managers
make decisions. Financial planning languages are particular kinds of decision
support systems that are employed for mathematical, statistical and forecasting
modelling. Both types of languages find applications in developing complicated
business model hypothetical representations of management problems.
Application generators
An application generator consists of a software system with number of program
modules, preprogrammed for various functions, so that the programmer or user
can simply state which function is needed for a particular application, and the
system will select the appropriate module and run a program to meet the user's
needs.
Table 3.1 summarizes some of the major difference between third-generation
languages (3GLs) and fourth-generation languages (4GLs.).
Table 3.1
Difference between 3 GLs and 4 GLs
Third-generation Languages Fourth-generation Languages
Intended for use by professional May be used by a non-programming
programmers. personnel as well as a professional
programmer.
Requires specification of how to Requires specification of what task is
perform task. to be performed (system determines
how to perform the task).
All alternatives must be specified. Default alternatives are built in; an end
user need not specify these alternatives
Require large number of procedural Require fewer instructions.
instructions.
Code may be difficult to read, Code is easy to understand and
understand and maintain. maintain because of English-like
commands.
Language developed for batch Language developed primarily for
operations. on-line use.
Can be difficult to learn. Easy to learn.
Difficult to debug. Easy to debug.
Typically file-oriented. Typically database-oriented.
Natural Languages
Natural languages are still in the developmental stages, but they promise to have
profound effect, particularly in the areas of artificial intelligence and export
systems. Natural languages have two characteristics:
l They are designed to make the connections that humans have with
computers more natural - more humanlike.
l They are designed to allow the computer to become "smarter" - to actually
simulate the learning process by remembering and improving upon earlier
information.
Two popular natural languages are LISP and PROLOG.
3.5 Compilers and Interpreters
For a high-level language to work on the computer it must be translated into
machine language. There are two kinds of translators - compilers and
interpreters. High-level languages are called either compiled languages or
interpreted languages.
In a compiled language, a translation program is run to convert the high-level
language program, which is called the source code, into a machine language code.
This translation process is called compilation.
The machine language code is called the object code and can be saved and either
run (executed) immediately or later. Some of the most widely used compiled
languages are COBOL, C, C ++, FORTRAN, etc.
In an interpreted language, a translation program converts each program
statement into machine code just before the program statement is to be executed.
Translation and execution occur immediately, one after another, one statement
at a time.
Unlike the compiled language, no object code is stored and there is no
compilation. The most frequently used interpreted language is BASIC.
Compiled languages are better than interpreted languages as they can be executed
faster and more efficiently once the object code has been obtained. On the other
hand, interpreted languages do not need to create object code and so are usually
easier to develop and test.
3.6 What is Software
As we know what computer is a machine which cannot do anything without
instructions from the user. In order to do any specific job you have to give a
sequence of instructions to the computer. This set of instructions in a proper
sequence is called a computer program. Software refers to the set of computer
programs that cause the hardware (computer system) to function in the desired
manner. Hardware means physical components of the computer system. We
can say that hardware which cannot perform any calculation, comparison or
manipulation without being instructed to do so. These instructions play a vital
role in the performance of a computer. A complete set of instructions written
to solve a problem on a computer is called software.
3.7 Types of Software
Computer software is normally classified into two broad categories:
(i) System Software
(ii) Application Software
3.7.1 System Software
System software includes general programs written for a computer. It consists
of pre-written programs and documentation supplied by the manufacturer along
with the computer. These programs are held permanently in the machine. The
primary objectives of this software are to:
(i) enhance the efficiency of hardware utilization, and
(ii) make computers simple to use.
The first objective is realized by that component of system software which is
commonly known as operating system.
System Software is a set of instruction to the machine to interpret and execute
application software, for example, language translators (called compilers and
interpreters), operating systems, utilities and special purpose software.
Language Translator
A language translator is a system software which translates a computer program
written by a user into a machine understandable form.
The most elemental form of programming uses only the binary digits 0 and 1,
which is directly understood by the electronic circuits. A program that have only
binary digits is called a machine language program. It is difficult to write or
understand machine language programs, as these consist of 0s and 1s.
Assembly language provides a significant improvement over machine language,
Assembly language programs are written using memonic codes like ADD,
STORE, etc., rather than their machine language representations in binary digits.
Therefore, programming in assembly language is easier. For its execution, it
needs to be translated into machine language code. This translation is done by
an assembler. Both machine language and assembly language programs are
machine dependant.
A program written in a high level language needs to be translated into machine
language code before execution. This translation is done either through a
complier or through an interpreter. A compiler is a translator program which
reads an entire program written in a high level language and converts it into
machine language code.
An interpreter on the other hand, is a translator which converts one statement of
the program into machine code, execute it and then goes on to perform the same
for the next statement, and it continues doing so till the end of the program or
on error occurrence.
Operating System
An operating system is the most important system software and is a must to
operate a computer system. An operating system manages a computer's
resources very effectively, takes care of scheduling multiple jobs for execution
and manages the flow of data and instructions between the input/output units and
the main memory.
The first operating system, called batch processing operating system was
developed for the second generation computers. This operating system executes
jobs serially one after another from a batch of jobs submitted for execution.
The central processing unit is kept busy only during the processing cycle of a
job and remains idle during the input and output operations. A multi programming
opening system handle multiple jobs simultaneously by overlapping the input/
output and processing cycles of various jobs.
Other types of operating system which are popular today are ‘multi-processing
operating systems’ and ‘real time operating systems’. A multi-processing
operating system uses multiple CPUs to process multiple jobs. A real time
operating system is a type of interactive operating system which strict time
limitation. Receiving and processing data is done quickly enough to produce
output, to control, direct or effect the outcome of ongoing activity. The
reservation system used by railway, airlines, hotel are examples of real time
applications.
The function of an operating system can be compared to the functions of a
principal in a school. The principal of the school provides an environment in
which the other employees can do useful work. The principal will do this by
allocating resources available such as allocating time for each period, allocating
classes to teachers and providing rooms for different classes etc. Similarly, an
operating system governs the working of the computer and input/output devices.
The operating system programs act as an interface between the user's programs
and the computer's components and help in the execution of user's programs.
The major functions of an operating system are:
(i) User identification and keeping of the resources used by the users. Thus
un-authorized users cannot use the computer.
(ii) Sharing of computer resources among many users. The sharing is
achieved by permitting simultaneous executions of more than one user
program. This is usually called multi-programming. A mix of programs
can keep the whole memory occupied, all devices active, and the control
unit and ALU constantly busy, thus increasing utilization of hardware.
(iii) Executive batches of programs, one after another, without human
intervention.
(iv) Protection of user's data and programs.
(v) Controlling the transfer of data and programs between the main memory
and secondary storage and other I/O devices.
(vi) Providing programs to select appropriate translators.
(vii) Providing facilities to detect and correct errors in a user's program.
An operating system understands a fixed set of commands. This set of commands
is often called job control language (JCL). The JCL commands are used by the
computer users to indicate their requirements to the operating system. The
operating system which is used with a micro-computer is called CP/M (control
program for microprocessor). Another operating system which is gaining
popularity and which is available on a variety of different machines is UNIX
(UNIX was developed by Bell laboratories). DOS is an operating system
commonly used in PCs.
The second objective of simplifying computer usage is achieved by enabling the
users to write their own programs in languages other than the machine language.
The only language understood by computers is machine language. If any other
language is used, the programs must first be translated into the machine language
before they can be executed. One of the most significant aspect of computers
is that such translations can be made automatically using other programs. A
computer manufacturer provides many programs for the translation of many
languages into the machine language. These programs are called translators or
compliers and form part of the system software.
We rarely talk about computer hardware alone. It is the hardware and software
both which make up a computer system. There is definitely some substance in
the argument that system software is as important, if not more, as its hardware.
Utility Software
Utility software may be considered as a system software which is used quite
often in the development of a program. Sort merge programs are used to sort
records in a particular manner or sequence. Such programs are normally provided
by the manufacturers. The programmer can also develop his own utility software
and keep it in the secondary memory of the computer.
3.7.2 Application Software
Application software is written to perform a specific task or process, such as
accounting, payroll, mailing list, result preparation and so on. The majority of
application software is written in high-level languages.
Assuming that the task to be carried out has been correctly identified, carefully
defined, the prospective user will come across the following alternative sources
for this application software.
(a) Write it yourself : The program written by the user can be the most
satisfactory solution. It will be an exact match to the needs of the
business. The program can grow with the business.
(b) General purpose application packages : Application packages refer
to a set of computer programs, which have been written to perform
specific, commonly required tasks. Each program is written in such a
way that it is applicable to a large number of users. The main advantage
is that it is relatively cheap as cost of the package is spread over a number
of customers. The major disadvantage of application package is that it is
not likely to fulfil all the requirements of the prospective users.
(c) Customer software : It refers to computer programs specially written
to match the exact needs of the user. It is precisely the same as getting
one's clothes stitched from a tailor to fit exactly rather than buying a
ready-made dress. The most important advantage is that such software
fulfils all the needs of the customer. The major disadvantage is that
customer software costs much more than general purpose application
software, because the package is specially made for one particular
customer.
Common Application Packages
Some of the common requirements of the users of personal computers have been
identified and common applications packages have been developed to meet their
needs. These packages include word processor, database processing, spreadsheet
calculations, mail-merge, presentations and communications (email). These
packages have been prepared so that they are simple to use. They also provide
graphical user interface to make them very user friendly. These packages are
readily available in the market and one can purchase them, install it on his/her
computer easily and start using the package.
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