Components of a Computer System and Modes
1.1.1 Hardware and Software Definitions
A computer system consists of hardware and software.
The hardware is the physical part of the system. All computer systems require at least
four types of hardware.
An input device is any piece of hardware that allows data to be transmitted to the
computer processor. No computer, however powerful, is of value unless it is possible to
give it instructions and data to be used when those instructions are carried out.
An output device is any piece of hardware that allows the computer processor to convey
information or the results of its processing. There is no point in having a computer
system carrying out processing of any sort unless the results of that processing can be
either reported or used to effect future input to the system.
Storage is any piece of hardware which can store data outside the processor in a form
which is suitable for input back into the processor. This is necessary because data must
be saved for future use if the processor is switched off and for transfer from one machine
Descriptions of the basic hardware types will be given in Chapter 5.
The software of a computer system is the various sets of instructions which tell the
system how to do things. These sets of instructions are collected together in workable
groups known as programs. Without programs of instructions computers would not be
able to function because they would not know what to do.
1.1.2 Different Software Types
Sets of instructions to make a computer do something are grouped together as
programs. These programs make up the software of a computer system.
Depending on the sort of task that a program is expected to accomplish they are grouped
into different types of software.
Operating system software is a program, or set of programs, which control the operation
of the computer system. They are responsible for the way that the pieces of hardware
communicate with each other and for monitoring the way that the hardware of the
system is used.
User interface software is used to provide a method of communication between the
person using the system and the system itself. Put very simply it is what you see on the
screen when you are using the computer.
Translator software is necessary because the computer uses a language that is difficult
for human beings to understand and a computer is not capable of understanding human
language. The translator software provides the computer with the equivalent of a
French-English dictionary so that it can look up what things mean.
Utilities, or utility programs, are system programs designed to carry out common tasks;
for instance the programs that control output to the printer or the storage of data.
Programming languages are used to write sets of instructions that the processor can
understand because it has a translator for that language. There are many different
programming languages, each of which has been designed for a particular type of
Common applications software include word processors, graphics, spreadsheets, and
many others. These are the programs that you, the user, uses to produce something
worthwhile on the computer.
All of these different software types will be covered in more detail later on in the work.
For the moment, the important thing is that you understand that there are different types
of software designed to carry out different tasks, and that you can give a brief
description of each.
1.1.3 Systems Software and Applications Packages
Computers are machines that can carry out operations very quickly. This does not mean
that they are in any way intelligent. However fast the machine can work, it is useless if it
does not know what to do. Computers need specific instructions for even the most trivial
of tasks. If a computer user had to supply these instructions there would be very few
people able to use one. Consequently, the manufacturer of the machine will provide
programs that are accessible to the user by using very simple commands, these
programs are the system software.
The operating system is the set of programs that control how the computer responds to
user requests. Examples that you may have used include DOS and Windows.
Utility programs are additional routines that can be added to an operating system or that
are available to the user within an operating system. An example that you may have on
your computer system would be a piece of back-up software that can be used to make
sure that you do not lose all your work when the computer fails.
Some frequently used routines are stored in such a way that they are accessible to
users. These routines are stored together in a system library, and form part of the
system software. This is something of a grey area between system software and
application software because application software also gives access to library areas.
Program translators are needed in order to allow users to produce programs in a simple
format which can then be translated into something which the computer will understand.
A piece of applications software is a program, or set of instructions, designed to make
the computer carry out some task. It differs from system software in that it makes the
computer do something that is useful for the user. Word word-processing software, or
Paintbrush graphics software are both examples of applications software because they
both allow the user to produce something that is of general use.
If the software can be used in many different situations to accomplish different things
then it is said to be generic software. For example a word processor can be used to write
a letter, or to produce a report, or type an essay,… A word processor is a piece of
If the software contains programs that allow lots of different tasks to be carried out,
together with a book of instructions telling the user how the software should be used,
then it is called an Applications Package.
An integrated package consists of several parts, each of which is an application package.
Further, the integrated package is designed so that users can easily move data between
the different parts of the integrated package. For example, if two of the parts are a
word-processor and a drawing package, users can move a drawing, created using the
drawing package, into the word processing package.
1.1.4 Modes of Computer System Use
An operating system is a set of software that controls the working of a computer system.
Just as it is possible to change a computer system by buying a new piece of hardware, it
is also possible to change it by altering the programs that are being used to control it.
We will be looking, in some detail, at the different effects that it is possible to get by
changing the operating system software at a later stage in this course. For now, we will
content ourselves with a brief look at four different groups of system software.
1. Batch processing.
The fundamental principle behind batch processing is that there are some jobs that need
to be done on a computer that take lots of time to do and stop the computer doing other
things. Big jobs that can be made to wait are put together in a “batch” which are all dealt
with when the computer is not needed for anything else. For instance, a bank’s computer
system is used a lot during the day-time by bank employees, but at night time it is used
very little. The bank statements that take a long time to print out are collected together
and sent through the system at night time when the computer is free.
2. Real-time processing.
A real-time processing system is one which makes decisions quickly enough to effect the
next input. For instance, if you are playing a computer game where you are driving a car
around a course, you would expect the computer to take account of the fact that you just
turned right before it decides the next position of your car. If the computer was not in
real time mode, your decisions would come too late to affect the game.
3. On-line processing.
On-line processing is when the user has direct contact with the processor. If you are
reading this on a stand alone computer then you are probably on-line because your
commands are being dealt with by the computer system as soon as you input them. This
is as opposed to…
4. Off-line processing.
Off-line processing is when the user (or input) does not have direct contact to the
A real-time system must be on-line because otherwise the input would not be able to
reach the processor fast enough to affect the output. A system where input at a keyboard
is stored on a disk before being input to the processor later, is an off-line system.
This section contains example questions based on the work in this first section of module
1. The work is of a very basic level because of its position in the syllabus, consequently
the number of questions is somewhat restricted.
Typical examiner’s comments follow each question.
1. Explain the difference between hardware and software. (2)
A. -Hardware comprises the physical parts of the computer system, while..
-software are the programs that make the machine produce useful results.
Notice that the answer suggested provides a link between the two terms. This was
expected because of the use of the words explain the difference in the question. There
are two marks available for the question so make sure that you have said two distinct
things. Make sure that the second point is not just the opposite of the first. In this
example there would be no mark for saying that software are the other parts that are not
2. Give two reasons why a computer system would need to have some type of external
storage device. (2)
A. -In order to store files when the power to the processor is switched off.
-In order to store files which are too large to be stored in the processor itself, until they
-To allow for the transfer of data from one machine to another.
Notice that the question asks for reasons why the system needs to have storage, NOT
for what is stored. Be careful to answer the question asked. Note that there are two
indicators in the question that you should give two answers, the word in bold and the
number of marks. This question does not ask for a comparison or an explanation, so
don’t give them. Notice that there are more than two acceptable answers. If you can
think of three then give them, the examiner will choose the two best, but never give
more than one extra answer because you then demonstrate that you are not sure and
the examiner will choose your first two answers, right or wrong.
3. Describe the difference between system software and application software. (2)
A. -System software controls how the computer system works while…
-application software allows the user to make the computer do something useful.
Again, this is a comparison type of question so the two parts of the answer should be
4. An integrated applications package contains a number of different pieces of generic
State what is meant by an integrated applications package and generic software. (3)
A. An integrated applications package contains
-a number of different pieces of software which…
-can communicate with each other in order to…
-allow the user to produce valuable work.
Generic software is
-software that can be used in many areas for different end products.
Notice the fact that there are three mark points for the first part of the answer, this does
not mean that all three marks can be gained by only answering one part. In this type of
question, some of the marks are always reserved for the last part of the question.
5. Give an example of a computer application which would use
(i) batch processing,
(ii) real-time processing
and give a reason why each of your suggestions is appropriate. (4)
A. (i) -Printing bank statements for all the bank’s customers…
-can be done at a time when other work is not being done.
(ii)-Playing a computer game because…
-you expect that any decision that you might make should be dealt with before the
computer makes its next move.
Notice that it is important to make a conscious decision about how the marks will
probably be awarded to stop you wasting time giving more thorough answers than
necessary. Also, there are certain standard answers that will always be right. Some
students decide to come up with something new in questions like this and, while initiative
is applauded, often don't explain their application well enough to get the mark. The
warning is always “Don’t throw marks away”.