Standard Grade Computing

System Software&

Operating Systems

What is Software

Software is the term that we use for all the programs and data that we use with a computer system.

Two types of software Programs - the instructions that the

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

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

Types of Program Software

Applications Software programs designed to carry out a

manual task (Word Processors, Databases, Graphics etc.)

Systems Software programs used to organise the

computer, handle its devices, manage memory etc.

Operating Systems

The operating system is the most important piece of system software.

The operating system that we are familiar with is Windowsxp

Operating Systems

DOS Old command-line operating system Requires users to memorise and enter all commands

UNIX Known for reliability Used by large companies and institutions Particularly multi-user environments

Windows Graphical User Interface Dominate the market

Linux Similar to UNIX but for PCs Source code is free! Worldwide community work to improve Linux

MacOS X The OS for Apple Macs

Operating Systems

Operating Systems

The operating system is a set of programs that give instructions to the computer

The operating system takes charge as soon as the computer is switched on

Everything that is going on in the computer is under the control of the operating system

Operating Systems

The OS is stored on hard disc and loaded into RAM when the computer starts up.

Some computers store their OS in ROM so that it cannot be erased by accident.

Functions of the operating system

Command language interpreter deals with the commands the user gives to the computer – the Human Computer Interface

Memory management which controls where programs and data are stored in memory

File management organises the data which is sent to backing storage and controls the loading of files into memory

Input/Output control deals with taking instructions from input devices and sending instructions to output devices

Job scheduler organises the way in which the different tasks are carried out

Types of operating system

An interactive operating system is one which runs continuously – taking instructions from the user and carrying them out. This is the type of operating system we are most familiar with.

A real-time operating system responds to input immediately. Automatic teller machines for banks are an example of real-time processing.

A batch operating system is used to run through a set of jobs which have been collected together. Processing of wages is an example of batch processing.

Background jobs

The operating system can have jobs working in the foreground and in the background

While you are word processing (the foreground job) the processor is idle for long periods. During this idle time the background job such as printing can take over the processor and carry out some printing tasks.C

To make it easy for the user to keep files tidy and easy to find they are grouped into named folders or directories.

Directories and Catalogues

This system of having folders within folders is called a hierarchical filing system.

More System Software

As well as the operating system there is other software called utility software.

Disk formatters, disk defragmenters and virus checkers are examples of utility software.

Low level languages

Computers use binary code (patterns of 1’s and 0’s) to represent all instructions and data

This is referred to as a low level language because it is at the level at which the computer works

Binary code is very difficult for computer programmers to understand and to correct errors1000100100100100110

High level languages

Because binary is so difficult to understand, programmers are more likely to write programs in a high level language such as Visual Basic

All high level languages use a lot of English words e.g. area = length * breadth

This makes programs easier to write, understand and to correct errors

Translating high level languages

Because high level languages are not in machine code (which the computer understands), they must be translated into machine code before they can be run

A portable computer program is one which can be run on different computers system types with little or no changes having to be made

Translator 1 – the Interpreter

The interpreter works by taking a line of high level code, translating it into machine code, then carrying out the instructions. It then goes to the next line of high level code and repeats the process.

High level instruction

Translation process

Instruction now in binary

Carry out instruction

Get next high level instructionC

The Interpreter

Good point It is easier to correct the errors in the program

Bad point The program can run very slowly because each

line of code is translated one at a time

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Translator 2 – the Compiler

The compiler works by taking the whole of the high level program (called the source code), and translating it into a machine code program (called the object code).

High level

program

Machine code

programCompile

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Source code

Object code

C

The Compiler

Good point The program will run much faster because it

will be in machine code

Bad point Because the program will end up in

machine code it will not be so easy to correct any errors that are in the program

C