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
Air conditioning controllers
Central heating controllers
Production line control
Hardware and Software
The parts of the computer system that can be touched e.g. printer
Input devices are used to get data into the computer so
that the CPU can process it to get the desired output.
Main (internal) memory
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
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
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.
Central Processing Unit
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/ backing Store
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
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.
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.
Controlling the OS
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
Graphical User Interfaces
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.
Command Line Interfaces
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.
Functions of an operating system
• 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.