THE SOFTWARE Computers need clear-cut instructions to tell them what to do, how to do, and when to do. A set of instructions to carry out these functions is called a programme. A group of such programmes that are put into a computer to operate and control its activities is called software.

Software contd… These programmes must reside in the internal storage (memory) to execute their instructions. Software is an essential requirement of computer systems.

Software contd.. The software may be broadly classified into two major categories System software Application software

System software System software may include the following types of software (a)Operating system (b)Language translators (c)Linker programmes (d)Loader programmes (e)Editor programmes (f)Utility programmes

Application software (a)Word processing packages (b)Electronic spreadsheet programmes (c)Database management systems (d)Graphics software

OPERATING SYSTEM The software that manages the resources of a computer system and schedules its operation is called the operating system.

Functions of OS To control and coordinate peripheral devices To monitor the use of the machine's resources To manage disk files where data and programmes are stored To help the application programmes execute its instructions To help the user develop programmes To deal with any faults

OS contd.. The operating system is usually available with hardware manufacturers An operating system that runs on one computer may not run on the other Popular operating systems include, among others, MS-DOS, Windows 95,98, 2000 Windows NT and UNIX.

UTILITY PROGRAMMES There are many tasks common to a variety of applications > Sorting a list in a desired sequence. > Merging of two programmes. > Copying a programme from one place to another. > Report writing.

Utility programmes contd… One need not write programmes for these tasks. They are standard and normally handled by what are known as utility programmes. Like operating systems, utility programmes are prewritten by the manufacturers and supplied with the hardware.

LANGUAGE TRANSLATORS Computers can understand instructions only when they are written in their own language called the machine language. a programme written in any other language should be translated into machine language. Special programmes called language processors are available to do this job.

Language translators These special programmes accept the user programmes and check each statement If it is grammatically correct, produce a corresponding set of machine code instructions Language processors are also known as translators

Language translators There are three forms of translators: 1.Compilers 2.Interpreters 3.Assemblers

Compilers 1.A compiler checks the entire user- written programme (known as the source programme) and if error- free, produces a complete programme in machine language (known as object programme). 2.The source programme is retained for possible modifications and corrections and the object programme is loaded into the computer for execution.

Interpreter –An interpreter does a similar job but in a different style –The interpreter (as the name implies) translates one statement at a time, and if error-free, executes it. –This continues till the last statement. –Thus an interpreter translates and executes the first instruction before it goes to the second, while a compiler translates the whole programme before execution.

Interpreter –The major differences between the two are –Error correction (called debugging) is much simpler in the case of the interpreter because it is done in stages. The compiler produces an error list for the entire programme at the end. –Interpreters take more time for the execution of a programme compared to compilers because a statement has to be translated every time it is read.

Assembler –As the computer understands only machine-code instructions, a programme written in assembly language must be translated into machine language before the programme is executed. –This translation programme is called the assembler. –Language translators are usually written and supplied by the hardware vendors.

LINKER AND LOADER PROGRAMMES –A linker is a system programme that links modules or programme segments together –The linker is responsible for producing an executable code by linking the object code with other library functions.

Loader –A loader is also a system programme that loads programmes stored in a programme library into memory for execution. –An example of a loader is the bootstrap loader that brings the operating system from the disk and loads it into the memory.

EDITOR PROGRAMMES –An editor is a system programme that is used to type in and edit text or programme statements. –All operating systems contain their own editors. –Word processing packages can also be used as editors.

APPLICATION PROGRAMMES –Whilean operating system makes the hardware run properly, application programmes make the hardware do useful work –Application programmes are specially prepared to do certain specific tasks.

APPLICATION PROGRAMMES – They can be classified into two categories. –1.Standard applications –2.Unique applications – Some applications are common for many organisations.

APPLICATION PROGRAMMES – Standard packages includes – Word Processing (WP) systems Electronic Spreadsheet – Database Management Systems (DBMS) – Graphic Packages (CAD/CAM) – Sales Ledger – Purchase Ledger – Statistical Analysis – Pay Roll

Unique programmes – There are situations where we may have to develop our own programmes to suit our unique requirements. Such programmes fall into the category of unique application packages.

PROGRAMMING LANGUAGES – The language used in the communication of computer instructions is known as the programming language. – The computer has its own language and any communication with the computer must be in its language or translated into this language.

Programming languages – Three levels of programming languages are available. –1.Machine languages (low level languages) –2.Assembly (or symbolic) languages. –3.Procedure-oriented languages (high level languages)