Designing the User Interface
Note: Much of the content of this chapter has already been covered in module 1 sections
1.2.3, 1.5.5, 2.1.3 and 2.1.4 and this chapter should be read in conjunction with these
3.4.1 Importance of Good Interface Design
However complex the software, however expensive and powerful the hardware, the system
is unusable if there is no intuitively simple to use interface with the human being who is in
control of the system or for whom the system is producing results. The Human Computer
Interface (HCI) must be unambiguous, allow the user to input all the data that the user
thinks important, and produce the output in an easily understandable form.
The intended user of the interface must be taken into account. The interface design for a
pre school playgroup to learn about numbers is going to be very different from the design of
an interface for the manager of a chemical plant to keep a check on the reactions around
the plant. The interface that this manager would use to study a particular reaction (perhaps
tables of figures, or graphs showing the different parameters of the reaction) is very
different from the interface the same person would use if they were wanting to see the flow
of a chemical around the whole site. This would probably be in the form of a diagrammatic
representation of the site. The circumstances under which the interface is to operate are
also important. In the last chapter mention was made of the nurse looking after a group of
patients. In those circumstances an audible warning that a problem may be occurring is far
more sensible than a visual one which may be ignored if the nurse’s attention is drawn away
from the screen. Finally, the designer of the interface needs to take account of the purpose
for which the interface was designed, namely the transfer of data into the system and the
communication of information from the system to the user. If the user is using the computer
to play a game, then the paramount importance of the interface is that it adds to the
enjoyment of the user.
Consideration of the purpose of the interface,
who it is for
what information needs to be conveyed
the circumstances under which the interface must operate
the effectiveness of the communication
the enjoyment obtained from using it
are all important when the interface is being designed.
3.4.2 Peripheral Hardware for a Given Application
This section deals with the needs of the application rather than the peripheral devices
themselves. For details of the devices the reader’s attention is drawn to Chapter 1.5.
When peripheral devices are chosen, a number of factors need to be taken into account.
Who are the people that are going to use the application? Specifically, consideration must be
given to their age (can they read is an obvious question), their ability with computer
systems, their understanding of the software in use (do they need to be given instruction
how to use it or do they know what is expected of them?), any physical disabilities which
may make some hardware impossible to use.
Is the system automated in any way? If so the peripherals may include sensors and
Under what circumstances will the system be used? If the input and output devices are to be
used in the open air then the environment will dictate some restrictions which would not be
necessary if the system was being used in a computer room.
The software that is being used. The software will dictate the type of input required and the
type of output that will be produced, consequently it will also have an influence on the
peripherals that are suitable for that input and output.
When answering questions drawn from this section, compare the requirements of the
system with the characteristics of the available hardware devices, and be prepared to state
why a particular choice has been made.
3.4.3 HCI Design Issues
Short Term and Long Term Memory
The information produced by a system can be of such a large volume that it is not possible
for all the information to be stored for future use by the user. Some of the information is
presented via the user computer interface, perhaps in the form of a scrolling graph. Such
data is very transitory in nature because the screen display is being constantly updated.
Such data is part of the short term memory. The long term memory is that which stores the
data for future reference.
This includes all the information that is presented by the system in such a way that it can be
seen with the eyes. This means that the information will be presented on a screen or on a
hardcopy produced by a printer. The size of individual pieces of information will be
important as will the contrast used and the type of font in the case of text.
Colour is an important part of any HCI. The contrasting use of colours can highlight the
more important information, or can be used to distinguish one type of information from
another. The different levels of contrast between colours are necessary if the individual
items of information are to stand out. Black on white provides the highest possible contrast,
while dark blue on black is very difficult to decipher.
The layout of the data on the screen is important. The eye naturally reads from left to right
and from top to bottom. This means that more important information should be positioned
toward the top and left of the screen. The volume of information on the screen at any one
time is also important because there is a limit to the amount that the eye can follow, and the
brain distinguish, in one sweep of the screen content. If the information should be seen in
an order, then the correct screen order is from top left to bottom right corners, as the eye
The content of the information presented is important because a user will soon begin to
ignore items of information that are constantly being put on the screen despite not being
necessary. Similarly, if a method is used to show that a piece of information needs urgent
attention, while the operator does not perceive the urgency, then all such highlighted
information may be begun to be ignored in the same way.
3.4.4 Styles of Interface
This work has all been covered in section 1.2.3, 2.1.3 and 2.2.3. Students should refer back
to these sections for any clarification required.
3.4.5 Characteristics of a User Interface
This work has all been covered in previous sections. Particular sections referred to are 1.2.3
and 2.2.3 for type of software interface, 1.5.5 for hardware interface and 3.3.5 for the type
of report produced.
Module 2 tests the design and implementation of interfaces. The topics are included in this
part of the syllabus so that candidates can be tested on the theory of interface design and
the appropriateness of interfaces in practical situations.
3.4.6 Speed Mismatch
A typical computer system will consist of the processor to do the necessary calculations or
other processing, the peripheral devices to allow input, output and storage of
data/information, and the human being that is using the computer.
The processor can carry out its side of the task at great speed while the human being is
very slow both at providing input and making sense of the output. This difference in speed is
known as the speed mismatch between the operator and the processor. Peripheral devices
work at far greater speeds than the human being, but are considerably slower than the
processor, consequently there are also speed mismatches on both communications
concerning peripherals. If there are enough computer systems, this speed mismatch does
not matter so much, but if there is a shortage of processing time, then a method needs to
be found to keep the slowest parts of the systems isolated from the processor. One way of
doing this is to use batch processing (see Chapter 1).
The speed mismatch causes more problems if the decisions of the computer need to be
acted upon immediately. If a computer is being used to control the insertion of the graphite
rods into a nuclear reactor, it may become important to ignore the human being once the
decision has been made and simply to report that an action has been taken after the event.
In this way the speed mismatch has been overcome by cutting out the slowest part of the
A company has a workforce of around 2000. Some work in the office using the computer
system for administrative tasks, while others use the computer system on the production
line for giving details of orders that need to be manufactured.
1. Describe the factors that would have been important in the design of the software
interfaces to be used by the office workers and the shop floor workers. (6)
A. -Ability of workers with computer systems..
-have they received training/are they used to computer use…
-The environment in which the system would be used…
-lighting conditions on the shop floor may be different to those in the office..
-colours will have to be different on the screen in order to maintain contrast.
-What output will be expected from the computer?..
-The office will probably use text while the..
-shop floor will probably need diagrammatic responses.
-The hardware that is going to be used to communicate in the HCI..
-will determine style of interface, e.g. touch screen input or keyboard.
Notes: Although the hardware has been mentioned briefly in passing, the answer must be
limited to software because of the question. These are standard answers taken from the
text. Each answer needs to be expanded a bit because of the word ‘describe’ in the
2. Select appropriate peripheral hardware for these two application areas, giving reasons
for your choices. (12)
-Keyboard/mouse for input because…
-input is likely to be character based owing to typical office tasks.
-Monitor/laser printer for output because..
-output needs to be checked and then high quality printout for documents to be sent
-Hard drive for storage because..
-of need to store and retrieve documents out of sequence.
-Touch screen for input because..
-dirty environment could damage other forms of input device.
-Plotter for output in order to..
-produce design quality drawings for use in manufacturing process.
-Hard drive for storage in order to..
-store number of high quality drawings.
-Necessary for communication, either between machines or to some central resource/LAN..
-requiring cabling/network cards.
Notes: The standard form of the hardware question requiring answers for
input/output/storage/ and communication where appropriate. In reality this is too big a
question to be asked in an examination, the normal question will be out of 3,4,6 or 8
dependent upon whether the question says state or describe and whether communications
play a sensible part in the application.
3. The office workers often have to key in the details of new members of the workforce. The
details of the worker are on a standard form which the new employee fills in. Explain how a
form based software interface would be useful to the worker who has to key in the data. (4)
A. -The interface will have specific areas to hold the answers to questions..
-these should match the positions of the answers on the paper form...
-making it difficult to put the details in the wrong place..
-or to miss any out.
-Validation routines will be set up on each data area..
-to check the data entry and reject anything not sensible.
-Some areas will not allow a non reply.
Notes: Again, standard answers which will gain full marks even if many of the points are
missing. There is an element of testing the candidate’s ability to analyse a situation here,
but the important point is to test whether the student understands the concept of a form
4. Explain the types of output that would be expected from the computer on the factory
production line, if it is used to control the speed of the production line as well as being used
as a tool for the workers. (4)
A. -Menu type of interface on the screen so that…
-a touch sensitive screen can be used for input.
-Hardcopy printout of the plans for products..
-produced by a plotter..
-so that they can be taken from the terminal and used at the point of manufacture.
-Sound so that..
-an alarm can be sounded if the line is travelling at the wrong speed.
5. Explain why speed mismatch would mean that the computer should be in control of the
speed of the production line. (3)
A. -Speed mismatch is the name given to the difference in reaction time of the operator
and the computer.
-The computer is able to take decisions very quickly, while the operator works very slowly..
-The decision to change the speed of the line must be taken very quickly or product will not
go through all the manufacturing processes, so the computer controls it.
Notes: There is virtually no other question that can be asked about the speed mismatch. It
is simply the difference in reaction time and if the candidate can relate that to the
application, they must get the marks.