Types and Components of Computer Systems - created from Mind Map

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What is a computer?

Hardware and Software

A computer is a machine that processes data.

For the IGCSE course we are mostly dealing with 'General Purpose Computers' which can be programmed to perform a variety of tasks, your computer at home is one of these. Embedded Computers are another type you will come across; these are often unseen and sit inside machines controlling their operation e.g. automatic washing machines. Most people don't think about washing machines etc. being controlled by a computer, but as an ICT student you should be aware that many systems are computer controlled e.g.

Automatic washing machines

Automatic cookers

Air conditioning controllers

Central heating controllers

Computer-controlled greenhouses

Burglar alarms

Production line control

Robots

Hardware

Software

The parts of the computer system that can be touched e.g. printer

Input Devices

Main (internal) memory

Random Access Memory

Read Only Memory

Output Devices

Central Processing Unit

Secondary/ backing Store

Input devices are used to get data into the computer so that the CPU can process it to get the desired output.

This is the place where data and programs can be stored so that the CPU can access them. The memory in a general purpose computer can be divided into two main types • RAM (Random Access Memory) • ROM (Read Only Memory)

Random Access Memory is volatile this means that the contents are lost when the power is switched off. The computer uses RAM to store the programs that are running and also the data needed by the programs.

Read Only Memory is non-volatile used to store instructions and data that must be kept even after the power is switched off.

Output devices are used to display processed data from the CPU.

The CPU is sometimes described as the 'brain' of the computer. Its job is to accept data from input devices and use (process) the data according to the instructions given by the software. Once the data has been processed it can be sent to an output device so that the operator can use it.

Secondary storage, also called 'backing store' does not lose its contents when the power is switched off. It is used to store data and programs so that they can be accessed when the computer is switched on next. The most common type of secondary storage on a PC is the hard drive.

The programs that control the hardware, you can't touch these.

Software means the part of a computer system that you cannot touch. This is easier to describe by example. • Operating System e.g. Microsoft Windows, Applications e.g. Word processors and computer games like Crysis, Utilities e.g. disk defragmenter. Are all examples of types of software. Don't get confused between the software and the DVD it is stored on. You can, of course, touch and hold the DVD, but the software is the data stored on it and you can't touch that.

Operating systems

Virtual Machine

Controlling the OS

Graphical User Interfaces

Command Line Interfaces

Functions of an operating system

Application Software

Utility Software

There are many different operating systems available, some you have to buy and others are free to anyone. The main idea you have to understand about operating systems is called the Virtual Machine. This needs a little bit of explaining!

When people use a PC they do not actually have to know about the complex internal workings of the computer before they can actually get it to do something For example saving a document often just requires a user to click 'Save' from a menu. The actual processes that occur to get the data from RAM onto a free area of the hard drive are handled by the OS. These complex processes are hidden from the user. The OS provides a virtual machine for the user to work with i.e. the user instructs the virtual machine what to do (e.g. save) and the OS tells the computer what to do so that it happens. The virtual machine hides the inner workings of the computer from the user.

Telling the operating system what to do requires a user interface that lets the user give instructions. There are two main types of user interface. • Graphical User Interface • Command Line User Interface

All operating systems do not look the same, MS Windows looks different from Mac OS X and they both look different from the GNOME desktop of some LINUX distributions. However these examples do have something in common. They are all Graphical User Interfaces or GUI's (pronounced gooey). These are designed to make operating the computer as easy as possible, they provide • Windows • Icons • Menus • Pointer Collectively these features are known as WIMP. The only one that might need explanations is ‘Icons’; these are pictures that represent something e.g. a text document icon on the desktop. This icon is not the document itself but it represents the document and when clicked will cause the document to be loaded.

Some operating systems have the option of a command line interface or a GUI; others only have a command line interface. A command line interface is not as easy to use as a GUI. Users have to type commands and there is no indication what commands are possible, so users have to know what they are doing! You can access the command prompt in MS Windows from the accessories folder in the programs menu.

• Input/ Output control • Handling Errors • Allocating resources to programs • Providing the user with an interface to control the computer • Handling files stored on a backing store

These are programs that perform tasks which would need to be done even if the computer did not exist. The following examples should help to describe application software. • Calculations - Spreadsheets software e.g. MS Excel • Accounts - Accountancy software e.g. Sage • Entertainment - Games e.g. EA Crysis • Letter writing - Word Processor e.g. MS Word

Programs that perform everyday tasks such as defragmenting a hard disc drive or performing a backup of data.