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SoftwareSoftware

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What is softwareWhat is software►SoftwareSoftware is the term that we use is the term that we use

for all the programs and data on for all the programs and data on a computer system.a computer system.

►Two types of softwareTwo types of software►ProgramProgram - the instructions that - the instructions that

the computer follows (e.g. a word the computer follows (e.g. a word processor or a game).processor or a game).

►DataData - what the programs - what the programs process (e.g. a word processing process (e.g. a word processing document or a saved game)document or a saved game)

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More on softwareMore on software

►Systems Software - Systems Software - programs used programs used to organise the computer, handle to organise the computer, handle its devices, manage memory etc its devices, manage memory etc i.e. The Operating System i.e. The Operating System

►Applications software Applications software programs programs designed to carry out a manual designed to carry out a manual task (Word Processors, Databases, task (Word Processors, Databases, Graphics etc.)Graphics etc.)

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The Operating SystemThe Operating System► The operating system (O/S) is the most The operating system (O/S) is the most

important important programprogram used by the used by the computer.computer. Usually the O/S is stored on hard disc Usually the O/S is stored on hard disc

and is loaded into RAM when the and is loaded into RAM when the computer starts up.computer starts up.

Some computers store their O/S in Some computers store their O/S in ROM so that it cannot be erased by ROM so that it cannot be erased by accident. ROM operating systems load accident. ROM operating systems load very quickly.very quickly.

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The Operating SystemThe Operating System

The operating system controls and The operating system controls and monitors the operation of the computer monitors the operation of the computer system.system.

Examples of operating systems which are:Examples of operating systems which are:

►Windows XP and Vista for the PCWindows XP and Vista for the PC►OS X for Apple OS X for Apple ►Unix for large fileservers and Unix for large fileservers and

networks.networks.

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Standard Functions of the Standard Functions of the OS.OS.

►User interfaceUser interface The means of communicating with the The means of communicating with the

computer system (Icons are provided computer system (Icons are provided by the operating system).by the operating system).

►Manages memoryManages memory The way that memory is allocated to The way that memory is allocated to

programs is controlled by the OS.programs is controlled by the OS.

►Controls input/outputControls input/output The access to all devices attached to The access to all devices attached to

the computer is controlled by the OS. the computer is controlled by the OS.

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More OS - Standard More OS - Standard FunctionsFunctions

► The filing system manages backing storageThe filing system manages backing storage The filing system will prevent two programs The filing system will prevent two programs

trying to access the same files at the same time.trying to access the same files at the same time.

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Resource allocationResource allocation

► Various techniques are used to prevent two programs Various techniques are used to prevent two programs demanding the same resource at the same time (e.g. two demanding the same resource at the same time (e.g. two programs can't both send files to the printer at the same programs can't both send files to the printer at the same time). time).

The resource allocation system also ensures that all programs running on the system receive as much processing time as possible.

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OS - Special FunctionsOS - Special Functions

►Multi-programmingMulti-programming Operating Systems allow more than one Operating Systems allow more than one

program to run on the system at the same program to run on the system at the same time. time.

Multi-accessMulti-access Some operating systems Some operating systems allow many users to use the same allow many users to use the same computer system at the same time. Any computer system at the same time. Any computer system used in this way will computer system used in this way will have a multi-access operating system. have a multi-access operating system.

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OS - Different modes of processingOS - Different modes of processing

►InteractiveInteractiveInteractive computer systems are programs Interactive computer systems are programs that allow users to enter data or commands. that allow users to enter data or commands. Most popular programs, such as word Most popular programs, such as word processors and spreadsheet applications, processors and spreadsheet applications, are interactive. In interactive processing, the are interactive. In interactive processing, the application responds to commands as application responds to commands as quickly as it can once they have been quickly as it can once they have been entered.entered.

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OS - Different modes of processingOS - Different modes of processing

►Real TimeReal TimeReal-time operating systems are systems Real-time operating systems are systems that respond to input that respond to input immediatelyimmediately. Automatic . Automatic teller machines for banks are an example of teller machines for banks are an example of real time processing.real time processing.

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OS - Different modes of processing OS - Different modes of processing

►Background job capabilityBackground job capability► Some operating systems allow a background Some operating systems allow a background

process to occur at the same time as a foreground process to occur at the same time as a foreground interactive process.interactive process.

► The foreground process is the one that accepts The foreground process is the one that accepts input from the keyboard, mouse, or other input input from the keyboard, mouse, or other input device. Background processes cannot accept device. Background processes cannot accept interactive input from a user, but they can access interactive input from a user, but they can access data stored on a disk. data stored on a disk.

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The The FilingFiling System System

Catalogue/DirectoryCatalogue/Directory► The contents of a hard discs are held in the directory (also The contents of a hard discs are held in the directory (also

called catalogue). The filing system reads this information called catalogue). The filing system reads this information so that it can find any file on the disc straight away.so that it can find any file on the disc straight away.

► Software can be stored on backing storage as files. There Software can be stored on backing storage as files. There are two types of files. are two types of files. ProgramProgram filesfiles (such as the operating system, (such as the operating system,

word processors etc). word processors etc). Data filesData files (such as graphics images, documents (such as graphics images, documents

etc).etc).

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Types of filing systemTypes of filing system

► A hierarchical filing A hierarchical filing system is one that uses system is one that uses directories to organise directories to organise files into a tree structure.files into a tree structure.

C:/ D:/

Computer

Drives

Folders

Files

► Hierarchical filing Hierarchical filing system system

► A filing system in which A filing system in which directories have files directories have files and subdirectories and subdirectories beneath them.beneath them.

A Hierarchical Filing Structure

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Types of accessTypes of access► Sequential AccessSequential Access

► To go from file A to file Z in a To go from file A to file Z in a sequential-access system, you sequential-access system, you must pass through all intervening must pass through all intervening files. files.

► Sequential access is sometimes Sequential access is sometimes called serial access.called serial access.

► Random AccessRandom Access► Refers to the ability to access data at Refers to the ability to access data at

random. In a random-access system, random. In a random-access system, you can jump directly to file Z. Disks you can jump directly to file Z. Disks are random access media, whereas are random access media, whereas tapes are sequential access media. tapes are sequential access media.

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Systems SoftwareSystems Software

► The operating system is just one example of systems The operating system is just one example of systems software.software.

► Other examples of systems software are:Other examples of systems software are: Anti-virus toolsAnti-virus tools Disk utilities Disk utilities Programming toolsProgramming tools Printer manager utilitiesPrinter manager utilities

► All these are examples of programs. Programs can be All these are examples of programs. Programs can be written in a number of different ways...written in a number of different ways...

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Low Level LanguagesLow Level Languages► Computers only understand binary!Computers only understand binary!► All programs have to end up in binary language in All programs have to end up in binary language in

order work.order work.► The binary language that the computer The binary language that the computer

understands is called understands is called MACHINE CODEMACHINE CODE► Machine code looks like this…Machine code looks like this…

00100111,01110100,1001000100100111,01110100,10010001► NOT very easy to understand. NOT very easy to understand. That’s why High That’s why High

Level Languages have been produced...Level Languages have been produced...

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High Level LanguagesHigh Level Languages► We use We use High Level LanguagesHigh Level Languages (HLLs) (HLLs)

because programming in low level because programming in low level languages like machine code is VERY languages like machine code is VERY difficult.difficult.

► High level languages make it easier for us to High level languages make it easier for us to write programs because we can use write programs because we can use commands that mean something (PRINT, commands that mean something (PRINT, END, IF, THEN).END, IF, THEN).

► High level language programs still have to High level language programs still have to be converted into machine code to work. be converted into machine code to work. This is done by a translator.This is done by a translator.

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Common features of High Common features of High Level LanguagesLevel Languages

► English like wordsEnglish like words and phrases as instructions eg. PRINT, and phrases as instructions eg. PRINT, IF, THEN, END, STOP, ELSE, OPEN etc.IF, THEN, END, STOP, ELSE, OPEN etc.

► Arithmetic operationsArithmetic operations such as multiply, divide, add subtract such as multiply, divide, add subtract etc.etc.

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Common features of High Common features of High Level LanguagesLevel Languages

►Must be translated into machine Must be translated into machine code. A special program (a type of code. A special program (a type of systems software) called a systems software) called a translatortranslator does this…. does this….

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Types of translatorTypes of translator

►1. Compiler1. Compiler►A program that translates A program that translates source codesource code

into into machine codemachine code. . ►Compilers create an Compilers create an executableexecutable

program. Programs produced by program. Programs produced by compilers run much faster than the compilers run much faster than the same programs executed by an same programs executed by an interpreter. interpreter.

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Types of translatorTypes of translator

►InterpreterInterpreter► An interpreter translates line by line. An interpreter translates line by line.

Each HLL statement is converted, in Each HLL statement is converted, in turn, into machine code and then turn, into machine code and then executed.executed.

► Interpreters are sometimes used during Interpreters are sometimes used during the development of a program, when a the development of a program, when a programmer wants to add small sections programmer wants to add small sections at a time and in education because they at a time and in education because they allow students to program interactively. allow students to program interactively.