Higher Grade Computing Homework Answers – Units 1 & 2
UNIT 1: COMPUTER SYSTEMS
Data Representation – Answers and Marking Scheme
Q1
Give two reasons why computers use the binary number system
•
Binary arithmetic is simple to represent using only 2 symbols 0 and 1.
•
Only two voltage levels so less chance of signal degradation.
•
Binary simplifies the number of arithmetic rules.
Any 2 – 1 mark each
2
Q2
Convert each of the following decimal numbers to their binary equivalent.
a) 23 - 10111
b) 45 - 101101
c) 100 - 1100100
d) 255 - 11111111
½ mark each – only full marks allowed (e.g. 0, 1 or 2)
Convert each of the following binary numbers into their decimal equivalent.
a) 1010 - 10
b) 100000 - 32
c) 101011 - 43
d) 11111111 - 255
½ mark each – only full marks allowed (e.g. 0, 1 or 2)
Give two reasons why using a sign bit to represent numbers is impractical
•
There are two values for 0
•
Carrying out addition and subtraction requires consideration of the signs of the
numbers and their relative magnitude.
1 mark each
2
Q5
Convert the following decimal numbers to 2’s complement form using an 8 bit string of digits.
a) –3 3 is 00000011 – 11111100+ 1 = 11111101
b) – 35 35 is 00100011 – 11011100 + 1 = 11011101
1 mark each
2
Q6
Floating point numbers are stored using a mantissa and an exponent.
a) What effect will increasing the size of the mantissa have?
Increasing the accuracy of the number
b) What effect will increasing the size of the exponent have?
Increasing the magnitude of the number
1 mark each
2
Q7
a) The 7 bit ASCII code can represent how many different characters?
128
b) Explain what method is used to encode Unicode.
Using 16 bits giving 65,536 possible symbols
1 mark each (look for more than just 16 bits in b)
2
Q8
a) Explain what is meant by the resolution of a graphic
The total number of pixels in an image.
b) Explain what is meant by the term bit-depth.
The number of bits used to represent each pixel.
1 mark for each
2
Q9
Give one advantage and one disadvantage of using bit mapped graphics
Advantages - Edit at pixel level, produce wider range of shapes and patterns.
Disadvantages – Large amount of storage space, image loses resolution (becomes jagged)
when scaled, does not take resolutions that are higher than the resolution of the image.
1 mark for each advan and 1 for each disadvan.
2
Q10
Describe two advantages of using vector graphic representation.
Do not lose image quality on scaling.
Less storage space than for bit mapped
Editable at object level
Can be grouped together.
Have resolution independence.
Any 2 for 1 mark each
2
Q3
Q4
1
2
2
Higher Grade Computing Homework Answers – Units 1 & 2
Total Marks
20
Computer Structure
Q1
Q2
Q3
Q4
Q5
Q6
Q7
Q8
Q9
What are the main components of a computer?
Central Processing Unit, Main Memory, Backing Store and peripheral (I/O) devices.
All 4 for 2 marks – ½ mark each, whole marks only.
What is the purpose of the data bus and what type of information is it likely to transmit?
It allows communication between the component parts of the computer (1 mark)
Data transmitted from main memory to CPU, input data from an external device, information
from external memory transmitted to main memory.
Any 1 well described for 1 mark
Explain the system of events in the fetch execute cycle.
The contents of the PC are copied into the MAR
The contents of memory at the location designated by the MAR are copied into the MDR.
PC is incremented
Contents of MDR are copied into the IR
Decode the instruction in the IR
Execute the instruction in the IR
All 6 steps in order – 2 marks. Any mistake 1 mark off
The computer has two types of memory, RAM and ROM. What are the differences between
the two and what is the main purpose of each type?
RAM is volatile, can be written to, and is used to hold programs and data currently being
used by the processor.
ROM is non-volatile, can only be read from and is used to hold programs and data that do
not change such as operating systems programs.
2 marks well explained, 1 mark weak explanation
Name the three parts of the CPU.
Arithmetic and Logic unit, Control Unit, Registers
All 3 for 2 marks, 2 for 1, 0 for 1
The control bus is not really a bus at all but a collection of lines which send signals to other
parts of the computer. Describe the function of three such lines.
Read/Write – Initiates a memory read or write.
Clock – generates a pulse to sychronises the components
Interrupt – tells the processor that an external event has occurred.
NMI – Non maskable interrupt cannot be ignored by the computer
Any 3 for 2 marks, 2 for 1, 0 for 1
a) Explain why the address bus is uni-directional. – The address to be accessed is
placed on the bus from the processor using the MAR (1)
a) Explain the function of the data bus. – To carry data placed either from the MDR in
the processor to a memory location whose address is specified by the value on the
address bus or vice versa from a memory location to the processor. (1)
2
Explain the concept of addressability with reference to the address bus.
The address bus carries the address of the data to be accessed on a memory read or write.
The number of addressable locations is given by the number of wires in the address bus and
2 to the power of the number of lines.
Well explained 2 marks, poor explanation 1 mark
A computer has a 32-bit address bus and a 64-bit data bus.
b) What is the word length of this computer? 64 bits
c) What is the maximum amount of memory which can be addressed by this
computer? 32GB
d) Without reference to cost, why might this computer not have the maximum amount
of memory? The memory modules available may not be large enough to give the
maximum.
e) What effect on the computer’s performance would there be if the width of the data
bus were increased? More data could be carried each cycle and therefore the
performance would increase.
2
Total Marks
2
2
2
2
2
2
2
1
1
1
1
20
Higher Grade Computing Homework Answers – Units 1 & 2
Measuring Performance
Q1
Q2
Q3
Q4
Q5
Q6
Q7
Q8
Q9
Q10
What factors can influence the MIP rate of measuring performance?
The clock speed of the processor, the speed of the buses, the speed of memory access and
the speed of execution of instructions.
2 for all 4, 1 for 2 or 3
Explain what is meant by the cycle time with reference to the clock speed.
All processor activities start on a pulse of the clock. The time between pulses of the clock is
called the cycle time. (2 marks well explained, 1 poor )
Explain why two computers rated at the same clock speed may not have an equivalent
performance.
One computer may process more instructions in each cycle than the other.
May process instructions in fewer cycles. 2 marks well explained, else 1
Explain what is meant by a benchmark test in measuring a computer’s performance and give
an example of one such benchmark.
A benchmark is a well defined standardised routine used to test the performance of computer
systems. Measure systems in terms of FLOPS. Whetstone (frequently used instructions) or
Drystone (Arithmetic instructions) Well explained with example 2 marks, poor 1
Explain the effect of the width of the data bus on a computer’s performance.
If the width of the data bus is the same as the word size then the computer will be more
efficient. If a 32 bit data bus carries 4bytes to the processor in one fetch this is far more
efficient that a 16 bit which would need two fetches to carry the same amount of data. 2
marks well explained, else 1
Why is an interface needed to connect peripherals to the system bus?
Peripherals work at different speeds, have their own language and deal with different data.
An interface compensates for these differences to ensure compatibility. 2 marks well
explained, else 1
Describe the standard functions of an interface.
Converts data e.g. ADC or DAC, holds data in a buffer, transmit control signals to the CPU,
and maintain status information. 2 marks well explained, else 1
Explain the difference between serial and parallel transmission.
Serial transmission sends 1 bit of every byte at a time down a single wire. Parallel send 1 8bit byte at a time down parallel wires. 1 mark for each well explained.
2
Explain why the increase in the width of the data bus can improve system performance.
A wider data bus can allow more data to pass to and from the processor in each cycle. It
generally means that each memory location will hold the width of the data bus so a 32 bit
data bus will transfer 4 bytes at a time and memory is likely to hold 4 byte per location. 2
marks well explained, else 1
Explain why the increase in the width of the address bus can improve system performance.
The wider an address bus is the more memory locations can be addressed. The number of
width of address bus
locations is given as 2
. 2 marks well explained, else 1
2
Total Marks
2
2
2
2
2
2
2
2
20
Peripherals
Q1
Q2
Q3
Q4
A peripheral device captures colour images and saves them to memory.
a) Describe how the color is represented using 24 bits
8 bits represent 256 different colours of each of red, blue and green. This generates a 24 bit
numeric code representing the colour. 1 mark
b) The image is saved with a resolution of 600dpi. How many pixels are required to save
an image of 6” x 4”. Give your answer in MB and show your working.
6 x 600 x 4 x 600 = 8,640,000pixels x 3 bytes = 25,920,000 bytes = 25312.5K = 24.72MB 1
mark off for each error
Explain how a buffer is used with a peripheral.
A buffer is an area of memory that is allocated to transferring data between the computer and
a peripheral. The buffer stores data until it can be dealt with. 1 for each point well
explained, 1 for 1 point or poor explanation
Explain the concept of spooling illustrating your answer with an example.
Spooling is when a large file is sent to a device like a printer which cannot cope with it all at
one and the file is written to an area of disk and dealt with from there. 1 mark for written to
disk, 1 mark for printing or networking spooler
State the hardware required in terms of peripherals to set up a computer system to produce a
catalogue for a garden centre. The finished catalogue will be taken on electronic media to a
printers.
Scanner, Digital camera, photo quality colour printer, CD Writer or similar
3
1
2
2
2
2
Higher Grade Computing Homework Answers – Units 1 & 2
Q5
Q6
Q7
Q8
½ mark for each, full marks only, colour & CD writer necessary
Justify the choice of two of these devices in terms of resolution, capacity, speed, cost and
compatibility. For each device look for technical apec of each category using all appropriate
categories. 1 mark off for each missing or wrong answer
Describe the features, uses and advantages of a solid state device such as a USB flash
drive.
Made up entirely from electronic components, no moving parts, Flash card in a camera, USB
memory stick, Adv – small and portable, USB means can be used on any computer with a
USB drive very easily. 2 for all 3, 1 for 2
c) What is the purpose of an interface? Making the appropriate connection so 2 devices
can work together. 1 mark
d) State the factors that have to be resolved by an interface.
Data format, parallel/serial interfacing, DAC/ADC, voltage, protocols, status signals, speed.
Describe the difference between parallel and serial interfaces
Serial works on sending individual bits using time divisions, whereas parallel uses space or
multiple paths to send bits in parallel
1 mark for each well explained.
Total marks
4
2
1
2
2
20
Networks
Q1
Q2
Q3
Q4
Q5
Q6
Q7
Q8
Q9
Explain the difference between LAN’s and WAN’s with reference to transmission media,
bandwidths and geographical spread.
LAN – twisted pair copper cables or co-axial, 100MB to desktop common, within a building,
campus etc. 1 mark all points covered
WAN – telephone lines, 56Kbits/s dial-up 512Kbits/s broadband, connecting a city, a large
company, the whole world e.g. Internet. 1 mark all points covered
Explain the difference between a mainframe computer with terminals and a network of
computers.
Single mainframe with lots of memory, terminals have no processor or disk.
Network has central file-server and computers as terminal each with processor, memory
and disk. 2 marks well explained each covered.
Explain the differences between client server and peer-to-peer networks.
Central server or servers and clients are computers on the network all logging into server.
Data all held on central server backup easier. P2P has no server, small network of
computers networked together, files spread all over so backup difficult. 2 marks both
networks addressed and 2 point made for each
On a LAN describe the functions of file, print and web servers.
File server deals with log-ins and hold all user files.
Print server handles print queues and directs output towards correct printer.
Web server deals with all Internet requests and handles router.
All 3 for 2 marks, 2 for 1
Describe a bus topology in terms of nodes and channels. Describe the consequences of
failure of a node and a channel.
There is a central channel from which can be attached spurs leading to stations called
nodes. If a channel fails the whole section of the network is down, but if a node fails only
the node is down. 1 for topology, 1 for failures of node and channel – need to show
knowledge of difference.
Describe the functions of a hub, switch and router on a network with particular reference to
the differences between a hub and a switch.
A hub is a multiport repeater on a network. A switch divides the network up into collision
domains and can be programmed (a switch is a programmable hub). A router is used to
link a network to the Internet.
1 for each – total 3
2
Explain why a network computer needs a network interface card (NIC).
A NIC provides a dedicated full-time connection the network and the network must pass
through the NIC. Good Explanation 1 mark
Explain briefly why networks are becoming increasingly widespread.
The cost of technology is dropping and the desire to communicate is strong. Any
organization with more than one computer is likely to network them, at least P2P. Good
explanation 2 marks, poor 1
Explain how a virus may be spread to a computer and how it then may take effect.
Via an attachment downloaded from e-mail, an infected floppy disk or CD-ROM, a malicious
Internet site. Lie dormant until an event triggers them, may be activated immediately. 1 for
1
4
2
2
2
2
3
2
2
Higher Grade Computing Homework Answers – Units 1 & 2
Q10
each point, max 2
The access a user has on the network depends on their permissions. Explain what is
meant by permissions giving as an example the permissions you may have on your own
folder and a shared folder on the network.
Permissions are the ability to write files into folders, read files, amend and create files and
folders on different parts of the network. Own folder full control, shared folder read only. 1
for each part, max 2
Total Marks
2
20
Software
Q1
Q2
Q3
Q4
Q5
Q6
Q7
Q8
Q9
Describe the function of a bootstrap loader program.
A bootstrap loader carries out a series of hardware checks and then loads in the next part of
the operating system. 1 mark well explained
Briefly describe the main purpose of each function of a single-user operating system
User Interface - checks command for errors and either performs command or reports error
and asks for correct input.
File Management – organizes files on backing storage (disks)
Memory management – organizes programs and data in RAM.
Input/Output managements – manages the peripherals inc disk drives.
Kernel – manages processes.
All 5 with short description for 3, 3 or 4 for 2, 2 for 1, naming only 0
1
Describe the purpose of each of: a) Virus checker – To check for viruses by monitoring the size of files, suspicious
activities and a signature.
b) Disk defragmenter – moves file around to fill up gaps and create contiguous file
structures.
1 for each well explained
Explain why there is a need for standard file formats.
In order for files to be portable across different applications. 1 mark
Describe the differences between a JPEG and GIF graphic.
A JPEG file is created by using a compression algorithm and is a lossy format.
A GIF file is based on an algorithm that creates a dictionary or codebook. GIFs preserve all
the precise shapes in an image (losless compression)
1 mark for each well explained.
Describe the types of software that are required to produce a school web site and explain
why you chose these types.
You will need software to create and edit graphics and real pictures, and software to create
the web pages and incorporate the media elements onto the pages including hyperlinks, and
turn the pages into HTML. 1 mark for graphics (also video or sound) and 1 for web
authoring described.
When selecting an Application package to perform a certain task the software compatibility
needs to be addressed. Describe the checks that need to be made for each of memory
requirements, storage requirements and operating systems.
a) Check that there will be enough free RAM to run the application after the operating
system is loaded.
b) Check that there is enough disk space to install the software and that there will be
enough space for large data files.
c) Check that the application will run on your version of the operating system.
1 for each point well explained.
Computer viruses are classed by three main types, file virus, boot sector virus and macro
virus. For each type describe how the virus is delivered and how it operates.
Usually delivered by e-mail or via a rogue disk or Internet site. File viruses attach themselves
to program files and when the program is loaded it is also loaded and activated.
Usually delivered via e-mail or from an Internet site. Boot sector virus infects executable code
found in system areas of the disk. The virus is read when the system is running and then
activated the next time the O/S is loaded.
Usually delivered by e-mail file transfer. Macro virus infects applications and causes a
sequence of actions in the application.
1 each for delivery method and effect
2
Describe the anti-virus technique of heuristic detection.
Heuristic detection approaches the problem through past knowledge. Finds new viruses by
finding signatures that resemble signatures used in the past.
1 for good explanation
1
5
3
1
2
2
3
3
Higher Grade Computing Homework Answers – Units 1 & 2
Software Development
Introduction
Q1
The software development process consists of seven stages. Name the seven
stages in order.
Analysis, design, implementation, testing, documentation, evaluation, maintenance.
1 mark for all 7 and 1 for order
2
Q2
The software development process is an iterative process. Explain the term iterative
as used in this case.
If an error is discovered in any stage of the analysis or design the stage is revisited
until the error has been fixed. 2 for well explained and 1 for poor explanation.
2
Q3
Name the documentation normally produced during the software development
process.
User Guide, Technical Guide, Installation Guide, Structured Listing.
2 marks all 4, 2 or 3 for 1
2
Q4
The software should have an appropriate user interface. Describe the factors that
should be taken into account when an appropriate user interface is designed.
Appropriate means that you need to take in the background and capabilities of
intended system users.
2 for well explained and 1 for poor explanation.
2
Q5
Describe what is meant by efficient computer software.
Efficient means that it will not make unreasonable demand on the hardware on
which it will run.
1
Q6
Describe what is meant by maintainable computer software.
Maintainable software must be written and documented in a way which makes
change simple and straightforward.
1
Total Marks
10
Analysis and Design Stages
Q1
Why may software developers not get the software correct at the first attempt?
Software systems can be very complex, unforeseen errors always creep in that take
time to solve and there could be problems with the client changing his/her mind.
2
All 3 for 2 marks, 2 for 1 and 0 for 1
Q2
Explain why regular feedback to members of the development team is important.
1
To enable personnel to discuss progress
Q3
Which process describes breaking a complex system down into more manageable
components.
The Top-Down Approach
1
Q4
Which document in the software development process is a legally binding contract?
Requirements Specification
1
Q5
What is the outcome of the analysis stage used to ascertain?
The main costs of the project, time taken to complete the project and hardware
required to run the system
2
6
Higher Grade Computing Homework Answers – Units 1 & 2
All 3 for 2 marks, 2 for 1and 0 for 1
Q6
What characteristics define software as robust?
The completed software system should be able to cope with many errors while
running
Total Marks
1
10
Implementation, Documentation, Evaluation and Maintenance Stages
Q1
Explain the purpose of testing at the implementation stage.
Testing finds faults in the software.
1
Q2
Explain the purpose of debugging software.
Debugging corrects the errors found in testing.
1
Q3
Explain the difference between testing and debugging.
1
Testing finds faults and debugging removes them
Q3
Explain the purpose of test data.
Test data exists to check the software meets the specification.
1
Q4
What is meant when we say that software is fit for purpose?
1
The final program meets the original specification.
Q5
Why is internal documentation important at the implementation stage?
It makes programs more readable, documents what the code does and records
changes made to the program
1
Q6
Describe two reasons why maintenance may be needed by software.
Bugs which appear over time may need fixed and legislation may be introduced
which requires changes to be made.
1
Q7
What is the advantage to a programmer to use modules from a module library?
The programmer knows that the module has been tested and works.
1
Q8
An array holds lists of student names and their marks in a test. Which standard
algorithm would be used to find: a) David Black – Linear search
b) The number of students scoring over 70% - counting occurrences
c) The top mark – finding the maximum
d) The bottom mark – finding the minimum
2
All 4 for 2 marks, 2or 3 for 1
Total Marks
10
Why is the design of the human computer interface so important?
The design of the HCI is important because this is the link between the user and the
computer. Even if the program is well written it is of no use if the user cannot use it.
1
Summary Questions
Q1
7
Higher Grade Computing Homework Answers – Units 1 & 2
Q2
Describe three types of maintenance activity.
Corrective maintenance is fixing bugs.
Adaptive maintenance is alterations required as a result of external forces.
Perfective maintenance is adding new features as a result of a user request.
All three for 2 marks, two for 1
2
Q3
What must be considered when creating test data?
Values within the acceptable range.
Values at the boundaries
Values outwith the acceptable range and silly or ridiculous data
1
Q4
What is acceptance testing?
Involves both the developer and user of the system. The user is given full access to
the system and must report any bugs, errors or misbehavior of the software.
1
Q5
What is the purpose of a structured walkthrough?
To allow a programmer to check for errors by working throught the program by hand
with test data.
1
Q6
A program can be described as correct but not necessarily efficient. How can this
statement be true?
A program may be correct in that it meets the requirements specification, but
inefficient as it may not make the best use of system resources.
1 for each point made.
2
Q8
Why does the use of a module library speed up the software development process?
Fully tested and documented code can be incorporated into a solution quickly and
with limited fuss.
2 for good explanation, 1 for poor explanation.
2
Total marks
10
Summary Questions
Q1
Explain what structure diagram is.
A structure diagram is a design representation which uses boxes to represent the
stages and processes of a programming design.
1
Q2
What is the purpose of pseudocode?
Pseudocode is a top down design methodology which allows the problem to be
described using a simple language which can then be translated into a high level
language.
1
Q3
Why must suitable test data be chosen to test a program?
Test data must be chosen so that a program can be proved to be error free.
1
Q4
What factors must be considered when creating test data?
Test data should test normal conditions, the boundaries and conditions outwith the
scope of the program.
2
Q5
What is meant by using test data in a dry run?
Working through the program by hand with the chosen test data.
1
Q6
Explain why a program may be described as robust.
A robust program will hold up to errors or unexpected conditions.
1
Q7
Explain why a program may be described as reliable.
A reliable program is able to react to the unexpected without crashing.
1
8
Higher Grade Computing Homework Answers – Units 1 & 2
Q8
Explain why a program may be described as portable.
A portable program may be moved to computer with a different operating system to
the one on which it was developed.
Total Marks
1
10
Summary Questions
Q1
What is a systems analyst?
A systems analyst observes, clarifies and models an existing system to assess its
suitability for computerization.
1
Q2
Describe three techniques used at the analysis stage of a software development
process.
Interviewing – the analyst asks the client questions to elicit the nature of the problem.
Observation – the analyst looks at the existing system and makes notes.
Inspecting information sources – the analyst collects examples of information that the
existing system already uses.
All 3 for 2 marks, 2 for 1. 0 for just naming.
2
Q3
What is a requirements specification?
A document developed by the systems analyst to carefully document the clients
needs. This is a legal document which will form the basis for the systems
development.
1
Q4
Describe briefly the role of the project manager.
The project manager is responsible for the project, appointed by the consultants,
supervises the project and carries out the initial stages.
1
Q5
What is the purpose of systems analysis?
The purpose of a systems analysis is to observe, clarify and model a system with a
view to developing an improved system.
1
Q6
Describe each of: The requirements elicitation. – Is the process gathering information to allow the
requirements specification to be made up. 1 mark
The requirements specification. – Includes a full description of the problem, all inputs
processes and outputs and represents an agreement between the client and the
developers. 2 marks well explained.
3
Total Marks
10
Summary Questions
Q1
Describe two features of a declarative language.
The ability to learn by adding to a knowledge base and the use of recursion.
2
Q2
Define an event in an event driven programming language.
Events include mouse clicks on icons, key presses etc.
1
Q3
Describe a benefit of using a scripting language.
A scripting language allows the user to extend the functionality of an application
package by programming a sequence of actions.
1
Q4
Give a reason why there was a need for scripting languages to develop.
There was a need for users to have more control over and expand the functionality
of an application package particularly database, spreadsheet and now web based
packages.
1
9
Higher Grade Computing Homework Answers – Units 1 & 2
Q5
A program can be compiled or interpreted to translate it from a high level language
to machine code. Describe the difference between the two.
A program that is compiled has all the source code translated in one go to produce
object code. An interpreted program is translated into machine code line by line
every time it is run.
2
Q6
Give an example of an object-oriented language and describe briefly how an objectoriented language may work.
Java – Object oriented programs are where a language model is arranged around
objects rather than actions and data rather than logic. We care about the objects
we want to manipulate rather than the logic required to manipulate them.
1
Total Marks
10
10