Hardware

Hardware

1.5.1 Control Unit, Memory Unit, and Arithmetic Logic Unit

The first thing to be said in this section, is what is not necessary. The three topics that are
listed in the heading would normally lead to the fetch- execute cycle, this does not come
into this module. Likewise, any complicated diagrams showing how the various parts of the
processor are connected up and communicate with each other do not appear in the
syllabus until the A2 section, next year. The requirements of this section are very simple,
they are restricted to a basic understanding of what these three parts of the processor are
meant to do.

Control Unit.
All computers follow instructions that are given to it in a program. These instructions are in
a particular order in the program, and following them, and carrying them out, will mean
that the computer has accomplished whatever task it was meant to do. Something, in the
computer, has to manage the instructions and make sure that all the other parts of the
processor do what they should be doing. This is the job of the control unit.
The control unit has three jobs
1. It has to decide which instruction to carry out next and then go and get it.
2. It has to decipher the instruction, in other words it has to work out what needs to be
done to carry the instruction out.
3. It has to tell other parts of the processor what they should do so that the instruction will
be carried out.

Arithmetic Logic Unit (ALU)
The ALU is where things are actually done in the processor.
1. The ALU contains circuitry that allows it to add numbers together (do arithmetic).
2. It allows for logic decisions to be made (If the value is negative then …, the part of the
processor that makes the decision is the ALU).
3. The third task of the ALU is to act as the gateway between the processor and the other
parts of the computer system. All input and output to and from the processor goes into the
ALU and waits there while the control unit decides what to do with it.

Memory Unit
The third part of the processor is where everything that the processor is going to use is
stored. This includes all the program instructions and all the data needed to carry out those
instructions. One of the jobs of the control unit is to be able to find the information stored
there when it is to be used.
The parts of the operating system, which the computer is using at the time also, need to be
stored in memory.
1.5.2 Types of Primary Memory

The first question that needs to be answered is “What is primary Memory?”
In section 1.5.1 the concept of the processor needing to store data of all types in the
memory was introduced. However, as those who have used a computer will know, there
are plenty of other places that a computer can store data or programs e.g. a disk drive or
a CDROM. These will be discussed in section 1.5.3. In the previous section it was stated
that any data or program instructions that the processor was to follow had to be in the
processor memory. Anything that is being held elsewhere, like on the surface of a disk
drive, cannot be used by the processor until it is moved into the processor’s memory.
Because it is so important it is called the primary memory. The primary memory of the
computer is the memory that is advertised as being “32 Mbytes of RAM”. This simply
describes the capacity of the memory.
There are a number of different types of memory in the processor.

1. ROM (Read Only Memory)
ROM is memory that cannot be altered. This means that even switching the computer off
will not effect the contents of the ROM. There is very little that needs to be stored in ROM
so it tends to be very small. In the past the whole operating system was stored on ROM,
but that means that if you want to use your computer in a different way or you want to
install the latest edition of an operating system to replace the one in use, you can’t
because the computer can’t delete the old one. When the computer is turned on it would be
there. For this reason the operating system is stored on the hard drive of a computer along
with all the other programs that may be used. A problem arises because when the
computer is switched on it needs the operating system to be able to do anything useful, so
a small program is stored on ROM whose job it is to go and get the operating system from
the hard drive so that the computer can work. This little program is called the bootstrap,
and the process of retrieving the operating system is known as booting.

2. RAM (Random Access Memory)
RAM stores the programs that are being used by the computer (including the operating
system) and the data that is being used with those programs. When the computer is
switched off all this data is lost. RAM is said to be volatile memory because it is so easily
changed, whereas ROM is non-volatile because it cannot change.
Notes:
1. There are many other types of primary memory that you may have heard of (PROM,
EPROM, EAROM, SRAM, DRAM,…). They are all a type of either RAM or ROM and you have
no need to learn about any of them, in fact it is probably better not to until the A2 part of
the course.
2. A typical question will ask for an example of what is stored in ROM and RAM. The safest
answers are the bootstrap being stored in ROM and user software and data being stored in
RAM. Problems arise if a student answers that the operating system is stored in ROM
because it can be, but in most micro systems it isn’t for the reasons given above. The
BIOS (if you don’t know what that is, don’t worry, it is not in the course) is another
problem. The BIOS itself includes user defined parameters and hence is not stored in ROM
entirely. In fact the BIOS tends to be stored in a special type of RAM which is refreshed
using battery power when the system is switched off. This is past the level of this course
and students are advised not to use this as an example of storage in ROM.
1.5.3 Secondary Storage Media

Primary memory is memory within the processor. It is here that the computer stores data
that are in current use because the control unit does not have direct access to data that is
stored anywhere outside the processor. However, the storage that is available in the
processor is limited in size and volatile. What is needed is something that is less temporary
in nature and that does not have the same restrictions as far as size is concerned. This will
be memory outside the processor. It is called secondary storage.
There are a number of different types of secondary storage that can be categorised
according to
Means by which the data is stored, optically or magnetically
The technique used for storage of the data, sequential storage or direct access storage
The capacity of the medium, how much can be stored on it
Portability of the medium, can it be moved around easily
Access times to the data stored.

1. Magnetic tape
Magnetic tape is still widely used, particularly in the form of tape streamers. The big
disadvantage of tape is that the access to the data stored is, by necessity, sequential which
makes it largely unsuitable for most data handling applications. However, large volumes of
data can be held and the medium is freely transportable. These qualities make it valuable
for producing back up copies of files stored on a computer system.
2.Magnetic floppy disk
Floppy disks hold a relatively small amount of information. Most software is too large to be
stored on a floppy disk, as are commercial files of data. However, a floppy disk is very
portable, allowing for easy communication of data from one stand-alone computer to
another. It is also readily available, almost all microcomputers having a floppy disk drive.
It is also convenient for storing those files that are particularly confidential because the
files cannot be broken into if they are being carried by the owner, or locked away in a
safe. Despite being direct, access times are slow because of the limited speed of rotation
possible and the relatively crude nature of the read heads.
3.Magnetic hard disk
Data is stored in the same way as on a floppy disk. The differences being that the hard
disk is made of a rigid material rather than a floppy plastic, and it is contained in a sealed
unit. These differences mean that the hard disk can rotate faster, the heads can get closer
to the surface meaning that the storage density can be greater, consequently that the
amount that can be stored is greater and that the access times are much faster. The hard
drive is likely to be the main secondary storage for a computer system, having very large
storage capacities. Although they can be portable, it is more likely that they will be fixed to
the chassis of the machine because of the tolerances that they have to work to.
4.CDROM
A CDROM is different from the storage devices so far mentioned because it is not
magnetic. A CDROM is an optical storage device, using the reflection of a laser off a pitted
surface to store information. Large quantities of data can be stored on the surface and it is
completely portable from one machine to another. In addition, most computer systems can
now be relied on to have a CD drive, and a CD is not alterable by the user. For these
reasons, manufacturers have tended to use CDs to produce software and large data files
like encyclopaedias. It is now possible to write to CDs by using a special peripheral device
called a CD writer and a special CD, but the above points are still true.
5.Others
There are many other types of secondary storage, two of which are worth a mention. Zip
drives are a more robust version of a floppy disk, having a faster access speed and a
greater capacity. They have become fairly popular for backing up work on
microcomputers. DVD is a relatively new technology that will probably replace CDROM as it
can store much larger quantities of data and allow access at high speed. For the purposes
of the syllabus, the original 4 types of secondary storage are quite enough at this level.

Speed of access to data.
Notice that there are no figures quoted for access times. There is little point in doing this
because access times vary according to the manufacturer and the point of development so
far reached. If the author were to quote a number, not only would it be wrong as far as
this work is concerned because there is such a wide range, but it would certainly be out of
date by the time you read it. In general terms the tape streamer is the slowest access
because of the way that the data is stored sequentially, then comes the floppy disk which
suffers because of the nature of the medium. Access times from CDROM and hard drives
are faster than the other two, but because there is such a range of both types of drive
available, it is impossible to say that one is faster than the other.
Capacity.
Again, much depends on the type of drive or size of medium being used. Tape streamers
come in different sizes, but tend to be comparable in capacity with smaller hard drives. Of
the different types of disk, a reasonable analogy is that a floppy would store the text from
a book, a CDROM would store a multi volume encyclopaedia, while a hard drive could store
a library.

Uses.
Obviously, no list of uses will be complete. However, there are some obvious uses for each
storage type which take into account the advantages and disadvantages of each.
A Tape Streamer is used for making backups of files held on computer systems. This
makes use of the fact that it can store a large amount of data, but the disadvantage of the
access being slow does not matter because it is rare that a backup file would be used
anyway.
A floppy disk has the advantage that it can be written onto and taken away from the
computer. Because of this it can be used for storing confidential files. Add to this the fact
that all computers can be relied on to have a floppy disk drive and it becomes a sensible
way of transferring information from one machine to another.
A hard drive has the advantages of being fast to access and also stores massive amounts
of data. These advantages mean that it is going to be used for storing software and user
files. The disadvantage of being attached to one machine is not important if the same users
always use the same machines, some other method of sharing will have to be devised if
this is not true.
A CDROM cannot be altered (unless it is a special re-writable). This disadvantage can be
turned into an advantage if the owner does not want the contents of the storage to be
altered. Examples of files stored on CDROM are software for import to a system and large
reference files like encyclopaedias.
1.5.4 Transfer of Data, including Buffers and Interrupts

There are two places where data can be stored in a computer system, the primary
memory and secondary storage. Sometimes it is necessary to transfer data from the
primary memory to secondary storage, perhaps because the computer is going to be
switched off in which case the data in primary memory would be lost. Sometimes it is
necessary to transfer from secondary storage to primary memory, perhaps because the
processor wants to use some data held in the secondary storage and, consequently, needs
to move the data into the primary memory first. Whichever direction the data is to be
transferred the method of transfer must be planned.
Normally the data would be transferred through a wire connecting the two storage areas
together. The type of wire and the different rules for data transfer are explained in section
1.6.4, sufficient for the moment is to have a picture of data travelling freely in both
directions.

Unfortunately, we know that things can’t be that simple. We know that primary memory is
part of the processor, and that anything that goes in or out of the processor must go
through the ALU, so the diagram should look like this

This causes a problem. The primary memory operates at great speed because it is part of
the processor, while the secondary storage is probably some sort of disk or tape which
(while it seems incredibly quick to us) is very slow at reading or writing the data, in
comparison. This means that the processor should be able to get on with something else
because the secondary storage is so slow. Unfortunately, it can’t because it needs the ALU
that is being used for the transfer of the data. This problem is overcome by the use of a
buffer.

Buffers.
The problem is caused because the secondary storage device is so slow compared to the
processor, the solution is to put a small amount of fast memory in to the system between
the ALU and the secondary storage device.
This means that the processor can send data very quickly (or receive it), and then get on
with something else while the storage device takes its time in reading (or sending) the
data. This small amount of memory between the two parts of the system is called a buffer.
Stage One: Filling the buffer from the processor

Stage Two: Emptying the buffer to storage

Interrupts.
This system is fine if the buffer can hold all the data that needs to be sent to the storage
device. However, if there is more data than will fit in the buffer, the storage device has to
be able to tell the processor (actually the control unit) that it has used up all the data in the
buffer and that it is ready for the next lot. This forces the processor to stop what it is doing
and fill the buffer up with more data. Because this message from the secondary device
makes the processor stop what it is doing it is called an interrupt. When the processor
receives the interrupt, the whole procedure is repeated.

Notes:
A buffer is a small amount of fast memory outside the processor that allows the processor
to get on with other work instead of being held up by the secondary device.
An interrupt is the message which the secondary device can send to the processor which
tells the processor that all the data in the buffer has been used up and that it wants some
more.
The example used here was communication between primary and secondary storage, but
the same is true for any communication between the processor and a peripheral device,
e.g. a printer or a keyboard.
The system is not really quite as simple as suggested here, but further complications can
wait until the second year of the course.
1.5.5 Common Peripheral Devices

Any hardware device that is part of the computer system but is not part of the processor
itself, is called a peripheral advice.
Peripheral devices can be categorised under four headings.

1. Communication devices.
These devices allow for communication between machines and will be covered in detail in
section 1.6.2.

2. Storage devices.
These devices, which provide for secondary storage in a computer system, have been
described in section 1.5.3.

3. Input devices.
There are too many different input devices to expect familiarity with all of them. However,
by inclusion in the syllabus there are some that must be understood. While this list is not
exhaustive, specific questions will not be asked about other input devices with the following
exceptions. There are some devices that are so common that any candidate taking an
exam in computing can be expected to have experience of using them, e.g. mouse,
keyboard. Additionally, candidates should be encouraged to learn about a variety of
contemporary devices so that they can use them when answering questions that ask for a
hardware configuration for a specific application.

a) Keyboard. A standard keyboard uses keys that stand for the different characters that
the computer recognises in its character set. Most keyboards contain the letters of the
alphabet, but not all do, for instance most calculator keyboards are very different, as are
the keyboards for use at cash machines. The characters needed for specialist use
machines are determined by the use to which the machine is to be put. Keyboards are the
most common form of input device to a system because they are universally available and
understood.
The common keyboard is known as the QWERTY keyboard because those are the first six
characters on the top line. The design is not very good for two reasons. First, the
arrangement of characters comes from the original typewriter whose keyboard was
arranged to be the most difficult to use in order to slow typists down so that they did not
jam the mechanism of the old machines. The second is that the keyboard itself is difficult
to use comfortably because of the way that the keys are arranged in rigid rows, making it
awkward to keep your arms comfortable while using it. The first problem is very difficult to
solve because of all the experienced operators that can use the present keyboard so well.
Retraining them to use a different arrangement of keys would not be feasible. Various
attempts have been made to address the second problem by arranging the keys in curves
that fit the palm of the hand rather than in straight lines. These are called natural or
ergonomic keyboards.
One problem with normal keyboards is that they are particularly prone to damage from dirt
or liquids because of the gaps between the keys. A different type of keyboard, where the
keys are simply part of a continuous surface which has areas on it, which are sensitive to
pressure, can overcome this problem. Called touch-sensitive keyboards, or concept
keyboards, they are ideal for use outside because rain will not damage them like a normal
keyboard.
A type of keyboard not yet mentioned is a musical keyboard. Normally arranged like a
piano keyboard these need a special piece of hardware to allow them to work properly,
known as a MIDI (musical instrument digital interface) this connects the musical keyboard
to the processor and allows data to be passed between the instrument and the processor.

b) Mouse. A mouse is a device designed to be used with a pointer on the screen. It is
particularly useful because it mimics the natural human reaction of being able to point at
something. A mouse is really two input devices in one. One is the movement around the
screen created by actually moving the mouse in a physical way, and the other is the ability
to select which is done by using a switch (the mouse buttons). Variations have been
developed which use the same basic principles but are designed for particular applications.
An example is the tracker ball used in many laptop computers. This is like an upside down
mouse where the user moves the ball directly rather than moving an object around a flat
surface. This is necessary because when using a laptop there may not be a flat surface
available.

c) Barcode readers. A barcode reader is a laser scanner that reads the reflected laser light
from a series of dark and light coloured lines of varying thickness. The different widths of
pairs of lines make up a code that can be converted into a number. This number can then
be used as the keyfield relating to a file of items that have been barcoded. The details of
the contents of the barcodes are not of importance to us in this section, except to say that
barcodes can easily be misread by the system, so one of the digits in the number is used
to check that the rest of the code has been read properly. This digit is called the check
digit, and will be discussed in more detail in section 3.3.4. Barcodes are particularly useful
because they do not rely on human beings to input the data, although, if the barcode is
damaged so that the laser scanner cannot read it properly, the digits represented by the
code are printed underneath so that they can be input by a user at a keyboard. Barcodes
are used where the data does not change, and so can be printed on original packaging.

d) MICR (magnetic ink character reader). This is a device that reads characters that are
printed on an original document at the time of it being created. The characters are printed
using magnetic ink. The value is that the characters are readable by humans and by
machines. The only common use for such characters is the data printed on the bottom of
cheques containing account identification.

e) OCR (optical character reader). This is a device that reads characters and can
distinguish between the different characters in a given character set. It works by
comparing the shape of a scanned character with a library of shapes that it is intended that
it should recognise. OCR tends to be an unreliable form of input and works more
effectively when it is restricted to having to recognise a standard character set produced
by printing rather than by using hand writing. OCR is used for reading post codes on
printed documents and also for reading documents for blind people, the contents of which
can be output using a voice synthesizer.

f) OMR (optical mark reader). This device can recognise the presence of a mark on a sheet
of paper. The position of the mark conveys information to the machine. For example a
school register may consist of a list of names of pupils in a class together with two columns
of small rectangles, one for present and one for absent. The same action (shading in a
rectangle) stands for both being present and being absent. The difference is the position
that the mark occupies on the paper. Printing in the sensitive areas of the sheet is done
using a special type of ink which the optical scanner does not see, that is why OMR
documents tend to be printed in a light blue or pink colour. The other standard use for OMR
documents is as multi choice examination answer sheets.

The big advantage of both OCR and OMR is that data can be input to a computer system
without having to be transcribed first, thereby cutting down the number of errors on data
input.

g) Scanners. A scanner is a device that converts a document into a series of pixels (picture
elements – these are small squares that, when put together, form a picture). The larger
the number of pixels, or conversely the smaller each individual pixel, the better the
definition of the final picture. There are different types of scanner, but all use the same
principle to create the image. A typical use for a scanner would be to input a picture of a
house so that it could be included with the details of a house that is for sale in an estate
agent’s publication.
A scanner is an input device, not to be confused with a plotter which is an output device.

h) Graphics Tablet. A graphics tablet is a flat surface on which a piece of paper is placed.
The user can then draw on the paper and the tablet will sense where the pencil is pointing
and transfer the line to the screen.

i) Microphones. Used to input sound to a computer system.

4. Output Devices
There are too many output devices to be able to write notes on all of them. Again, the
same thing is true about output as is true about input, that it is important to know about
those devices stated in the syllabus and also a range of devices that will allow for sensible
decisions about peripheral devices to be made for a given scenario in a question.

a) Screens. Monitor screens are categorised according to the obvious colour/monochrome,
also according to the number of pixels that there are on the screen. The more pixels there
are, the better the picture will be, this is known as the screen resolution. This is being
typed using a very low resolution, monochrome screen. If you consider the contents, there
is no reason for any further sophistication to be necessary. However, a computer system
running a modern game program will need colour and many more pixels in order to
produce a satisfactory picture. The more pixels that there are on the screen, the higher the
resolution is said to be.
A particular type of screen, called a touchscreen, acts as both an input device and an
output device. Information is output by the system onto the screen and the user is invited
to answer questions or make choices by pointing at a particular area of the screen. The
device can sense where the user is pointing and can report the position to the processor.
The processor can then deduce what the user’s reply was according to the position that
was pointed to. Touchscreens are particularly useful in areas where keyboards are not
appropriate, e.g. where the device may suffer from vandalism. They are also useful for
users who would find difficulty using other input devices, e.g. very young children who
want to be able to draw on a screen.

b) Printers. A printer is a device which provides the user with an output from the system
which is permanent. This output is known as hard copy, so a printer is a device which
produces hard copy. There are many different types of printer and the student should be
aware of a number of them, their uses, advantages and disadvantages. However, there is
no need to understand how they work.
The first type is a dot matrix printer. These tend to be slow, and the output is particularly
poor quality. The big advantage is that the output is produced by using pins to strike at the
surface of the paper. Because of the physical nature of the way that the printout is
produced, it is possible to obtain multiple copies by using carbon paper or self carbonating
paper. A good example of this is the receipt that a shopper is presented with if buying
something using a credit card, there are two copies produced, back to back, one for the
shop to keep and one for the buyer to take away with them.
Ink jet printers, which produce output by spraying ink on to the paper could not produce
the two copies that the dot matrix can, but it can produce much better quality and in
colour, at low cost. This makes ink jet printers ideal for home use.
Laser printers can produce very high quality work at high speed. The cost is more than
with the other types but used where it is necessary to give a good impression, for instance
sending letters from a solicitor’s office to clients.
Plotters are a type of printer designed for drawing lines and geometric designs rather than
for producing characters. The image is created by pens being moved across a piece of
paper, under the command of the processor. Plotters tend to be used for drawing
blueprints, perhaps in an architect’s office to produce detailed drawings of buildings for
builders to follow.

c) Speakers. Used to output sound from a computer system.

There are many other peripheral devices and, as has been mentioned, a knowledge of
some others will not come amiss, however that is enough to be able to answer questions in
the exam. The questions will normally take the form of presenting a scenario and then
asking for a description of the hardware required. The important thing to remember is how
the marks will be awarded. There will not be a mark for every device mentioned, but the
candidate will be expected to give sensible suggestions for each of the four areas of
peripherals mentioned at the start of this section. In other words the mark will not be for a
keyboard or a mouse, but for suggesting sensible methods of input to the system.
Example Questions.

1. State three functions of the arithmetic logic unit. (3)
A. 1. Any arithmetic is carried out in the ALU. (This normally takes the form of addition,
and the result is stored in the ALU temporarily before being returned to the memory)
2. Logical decisions can be made by the processor. (The processor can use the ALU to
decide whether one value is greater than another, or if one is negative,…, and then make
decisions based on the answers)
3. Communication with peripheral devices is carried out via the ALU. (All data which is to
be used by the processor has to be stored in the memory. Any item of data which is bound
for the memory must be stored temporarily in the ALU while the processor decides where it
is going to be stored)
Notice that the question asked for three answers. The sensible response would seem to be
to number them. The expected answers are the three single line responses. The contents
of the brackets give extra information which would not be expected in this question.
However, if the question had said ‘Describe…’ or ‘Explain…’ instead of ‘State…’, then the
question would have been worth 6 marks, and some extra detail, for instance the contents
of the brackets, would have been necessary.

2. a) State two ways that RAM and ROM memory differ. (2)
b) Explain what types of data would be stored in each of RAM and ROM memory, giving
reasons for your answers. (4)
A. a) -RAM is volatile (will lose its contents when the power is switched off), while ROM is
not.
-The contents of RAM can be altered, whereas the data stored in ROM cannot be altered.
b) -RAM would contain user files and software that is in current use.
-RAM is used for these files because they have to be alterable, and the user will want to
use different software from time to time, implying that the original software will need to be
erased so that it can be replaced. Losing these files when the machine is switched off is not
a problem because they will have been saved on secondary storage.
-ROM is used to store the bootstrap program.
-ROM is used because when the computer is initially switched on there must be a program
present that can be used to load up the rest of the operating system from secondary
storage. This program must not be altered because without it the computer cannot start to
work.
Notice the way that the answers have been phrased in part (a). The question asked for a
comparison of ROM and RAM so both need to be mentioned when you are giving an
answer. To say that RAM is volatile is true, but does not answer the question until you say
that ROM is not.
Part (b) is asking for reasons to be given. Notice that the reasons given related to the
answers given in part (a). The part (b) answer is not, “user files because there is more
space in RAM”, although that could be right if phrased a little more carefully.

3. A student has a home computer system.
State what storage devices would be used on a home computer system and justify the
need for each one. (8)
A. -Hard disk…
-to store software and user files (e.g. word processor and essays)
-Floppy disk drive…
-to enable work to be transported between school and home so that it can be continued in
the evening
-CDROM…
-to allow the import of new games to the PC.
-Zip drive…
-to back up the files, so that important work is not lost if the hard disk crashes.
Notice that the question does not specify how many devices should be mentioned.
However, each device has to be named and justified (2 marks) and there are 8 marks for
the question, so four devices seems sensible. What happened to tape? After all that is the
first secondary storage that was mentioned in the text. Tape is not sensible in this
example, there is not a big enough volume of data to make a tapestreamer worthwhile,
and the old cassette tape is an antique by now. Consequently, a tape device does not fit
the application given. Notice, also, the way that the justification for each of the devices was
linked to the application, for a floppy drive, the answer did not just say that it could be
used to transport files, but it gave a good reason for wanting to do so in this case.

4. Describe how buffers and interrupts can assist in the transfer of data between primary
memory and a secondary storage device. (4)
A. For the purposes of this answer I will assume that data is being transferred from the
processor to the secondary storage.
-Buffer is an area of fast access storage..
-which can be filled by the processor and then emptied at slower speed by the secondary
storage device…
-allowing the processor to continue with other tasks.
-When the secondary device has used the contents of the buffer…
-it needs to tell the processor that it requires more data…
-this is done by sending a message to the processor, called an interrupt.
Notice that the answer describes transfer of data from the processor to the peripheral.
Transfer in the other direction is equally valid and gives rise to a similar answer. However,
if the two answers are mixed together then it produces a confused, and often, wrong,
answer. This is why the first statement is important as it has set the parameters by which
the question will be answered. You don’t have to say this in your answer, but it makes
clear what is being done.
Also, there are more mark points than there are marks available. Hopefully, you are
getting used to this because it is generally true in most questions. In this question there
are obviously two points for interrupts and two for buffers, but in order to get the marks
you must make sure that the definition appears somewhere. So, for the interrupt, you
need to earn the last mark point, otherwise you haven’t defined what an interrupt is.

5. A department store decides to place a computer system by the main entrance to the
store so that customers can find out whereabouts in the store items are available. The
different departments remain in the same places, but the articles available in each
department change on a regular basis. State a sensible hardware design for such a
computer system, giving reasons for your choices of hardware. (6)
A. Input:
-Touchscreen
-Some protection against vandalism/restricts user access to contents of menu system
displayed/simple to use because it uses human reaction of pointing so no training
necessary
Output:
-(Touchscreen)/printer
-Touchscreen outputs choices for user to select from/printer available for producing
hardcopy as a permanent record for the customer
Storage:
-Hard drive/CDROM
-Hard drive necessary to store details of the products on sale because of the large number
of changes that occur in this file. CDROM used to keep the store plan and the location of
the departments as these do not change.
Notice the large number of possible mark points. Also the way that the marks are split up.
In this type of question you can’t expect a lot of marks for simply writing down a long list
of peripheral devices, the marks are split up according to the four types of peripheral
mentioned in section 1.5.5. In reality, this question would probably have talked about such
systems being available throughout the store, but this would mean that they would be able
to communicate with one another. As communication comes in the next section it was left
out of this example question, but such a question would normally have 8 marks, 2 marks
for each of the types of peripheral.