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3.0 Computer software

A computer is a machine that is dumb and unintelligible and it remains so until told to do

otherwise. One way to do this is to communicate with the computer using programming

languages understood by the computer. These programming languages will cause the computer

to perform certain tasks.

3.1 Software

This is a general term that applies to any program (set if instructions) that can be loaded into a

computer from any source. These programs tell the computer what it should do. Generally, there

are two types of softwareoperating system software and application software.

3.1.1 Operating system software

Is a program that initiates and controls the operation of the computer. This software manages

most of the computer activities which could include maintenance of files, resources and running

of application software. Operating system software controls the flow of information through the

computer from the input, processing to the output. It passes control from one program to another

under a system of priority when more than one application program occupies the main storage. It

furnishes a complete record of what took place during processing events. It also provides error

correction routines. That is why it is referred to as resource manager. Also operating system

software can be used to save, name, retrieve and maintain application packages on the

computers. It also help in managing peripherals such as printers, plotters,, keyboards and disk

drives, hence, it is also called a file manager. Examples of operating system software are UNIX,

Microsoft Window 2000, Win 2003, WinXP, MS-DOS etc.


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3.1.2 Application software

Are programs written for general use. They are of two types- user-defined (or specialist)

application software and application package.

1. User-defined application software: are those that are specially designed and tailored tomeet the specific needs of individuals, corporate bodies or establishments. Examples of

these types of software are used by banks for on-line transactions, payroll in agencies and

schools, stock control program and all those used by network service providers in

marketing competitions. E.g MTN, CELTEL, GLO. Such software are usually very

expensive to design.

2. Application packages: these are programs designed for particular types of problems.Since they are for general and unrestricted use, they are mostly cheap and mass-

produced. Application packages falls into the following categories:

Commercial software: these are software that are available and offered for salefor commercial purposes. E.g Microsoft word processor, spreadsheets, computer

graphics

Public-domain software: are software that are available for interested users.They can be duplicated without infringement of copyright. They can be

downloaded via the internet.

Sharewares: are those that are also distributed free of charge, although you couldasked to donate some money for some cause of global concern. e.g wikipedia

Freeware: are groups of software that are also available to interested users free ofcharge. e.g internet explorer, adobe reader

Rentwares: are software that are leased out to user for a token of fee.There are other categories of software that are designed for protective purposes and language

development. These are the utility software and language development software. Utility software

are variety of different programs designed to aid in computer system maintenance. eg. Virus

protection (antivirus), disk back-up, hardware analysis and troubleshooting, memory

management and peripheral supports. On the other hand, language development software are

used by software developers to write programs.


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3.2 Programming languages

Are all the technical activities involved in the production of a program, including analysis of

requirements and all stages of design and implementation. It can also be defined as the coding

and testing of a program.

3.2.1 Classification of programming language

1. Machine language is the only language that can be understood by a computerwithout translation program. This language is written in strings of binary digits 0

and 1. The circuitry of a computer is wired in such a way that it immediately

recognizes the machine language and converts it to electrical signals needed to run

the computer. For example, in the study on how a microprocessor works and control

systems such as dishwasher, cloth washing machines and all that, you will need to to

write programs using the data sheets such as Intel 8085 data book. Example of a

machine code is

1000001111000000011111111111000000000

The code could tell the computer to drain water or turn on the tap.

2. Assembly languageThe next level of programming language is the assembly (or low-level) language,

which consists of a variety of programming languages in which the control and data

structure directly reflects the underlying machine architecture. Such languages

substitutes letters and symbols for strings of binary digits used in machine codes.

They are called symbolic language or pseudo-language the letters are called

mnemonics (a shorthand or help). The programs are called assemblers and are

generally classified as low-level languages. Although assembly language is much

more convenient than machine language, it still requires that the user be familiar with

computer set of instruction mnemonics.

3. High level language


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A large number of high level languages (HLL) have been developed to overcome the

difficulties associated with assembly and machine languages. They are simpler to

learn and use. They make it possible to communicate with a computer using English-

level language and mathematical symbols without the need for detailed knowledge of

the computers internal architecture or instruction set. High-level languages are

known as problem-oriented languages (POL). They include the following:

COBOL: Common Business Oriented Language

BASIC: Beginners All-purpose Symbolic Instruction Codes

ALGOL: ALGOrithmetic Language

FORTRAN: FORmula TRANslation

Others are PASCAL, C++, JAVA etc

All programs written in high-level language must exist in two forms before they are executed by

the computer tom produce the desired results. These states are source and object programs.

3.2.2 Source program

Any program written in HLL or LLL is called a source program. Such a program cannot beexecuted or operated upon by the computer until it has been translated into machine language.


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3.2.3 Object program

Is obtained when a source program is translated using an interpreter, compiler or assembler.

Source programs are translated into object programs internally by the computer.

3.2.4 Translator

Is a program that converts another program written in one language to the equivalent program in

another language. Three types of translators are assemblers, compilers and interpreters.

i. Assemblers: is a program that takes as input a program written in assembly

language and translate it into machine codes

ii Compiler: is a special program which translates the source program of

a high-level language in the object program into machine codes. A

compiler translates the entire program before executing it. Figure 3.1 gives

the process of compilation.

CompilerSource program Object program

Figure 3.1 Process of compilation


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3.2.5 Interpreters

High-level language can also be translated into machine language by programs called

interpreters. An interpreter is a language processor that analyses a line of code and then carries

out specified actions, rather than producing a machine code translation to be executed.

Exercise

Explain the difference between an interpreter and compiler.


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