AS Level
Computing
COMP2 – Computer Components, The Stored Program Concept and the
Internet
Mark scheme
2510
June 2015
Version: Final Mark Scheme
Mark schemes are prepared by the Lead Assessment Writer and considered, together with the
relevant questions, by a panel of subject teachers. This mark scheme includes any amendments
made at the standardisation events which all associates participate in and is the scheme which was
used by them in this examination. The standardisation process ensures that the mark scheme covers
the students’ responses to questions and that every associate understands and applies it in the same
correct way. As preparation for standardisation each associate analyses a number of students’
scripts. Alternative answers not already covered by the mark scheme are discussed and legislated
for. If, after the standardisation process, associates encounter unusual answers which have not been
raised they are required to refer these to the Lead Assessment Writer.
It must be stressed that a mark scheme is a working document, in many cases further developed and
expanded on the basis of students’ reactions to a particular paper. Assumptions about future mark
schemes on the basis of one year’s document should be avoided; whilst the guiding principles of
assessment remain constant, details will change, depending on the content of a particular
examination paper.
Further copies of this mark scheme are available from aqa.org.uk
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MARK SCHEME – A Level Computing – COMP2 – June 2015
The following annotation is used in the mark scheme:
; - means a single mark
// - means alternative response
/ - means an alternative word or sub-phrase
A - means acceptable creditworthy answer
R - means reject answer as not creditworthy
NE - means not enough
I - means ignore
DPT - means "Don't penalise twice". In some questions a specific error made by a candidate, if
repeated, could result in the loss of more than one mark. The DPT label indicates that this
mistake should only result in a candidate losing one mark, on the first occasion that the
error is made. Provided that the answer remains understandable, subsequent marks
should be awarded as if the error was not being repeated'.
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MARK SCHEME – A Level Computing – COMP2 – June 2015
Qu Part Sub- Marking Guidance Marks Comments
part
1 a operand; 1
R operand code
1 b i PC 0010; 3
MAR 0001;
MBR 00100100;
1 b ii The instruction is held in the CIR // instruction in MAX
CIR is decoded; A IR 3
The control unit/instruction decoder decodes the
instruction;
NE the processor decodes the instruction
Instruction will be split into opcode and operand;
R if it is implied that a register will do this
splitting/decoding
Relevant part of processor/CPU executes
instruction // using ALU to perform calculations;
A instruction executed by the control unit / ALU
NE processor executes instruction
Further memory fetches/saves carried out if
required;
Result of computation stored in
accumulator/register/written to main memory;
Status register updated;
If jump/branch instruction PC is updated;
By example:
Will ADD contents memory location 0100 to
accumulator;
1 c The current value in the accumulator would be MAX
stored in (memory) address/location 0011/3; 1
Number 011/3 stored in (memory)
address/location 0011/3;
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MARK SCHEME – A Level Computing – COMP2 – June 2015
2 a A language that is close to the hardware; MAX
1
Language that interacts with basic
hardware/tasks of the computer;
Commands map directly/very closely to
processor instruction set;
One instruction maps to one processor
instruction;
A processor/architecture dependent language //
language that is not portable;
NE. machine code or assembly language
R. directly executable by the processor
2 b HLL allows several machine code statements to MAX
be replaced by one high level statement // HLL 2
program shorter that its low level equivalent;
HLL program expressed in language that is
human-oriented/uses English-like keywords;
A structured English
NE written in English / closer to English
Allow programmers to:
use meaningful identifier names;
use procedures/functions/subroutines/libraries;
use programming structures such as IF THEN
ELSE/ REPEAT UNTIL;
use data structures such as arrays/lists;
Easier to see logic/structure of program/ what is
to be executed;
A easier to spot/check errors // easier to debug;
Can maintain one codebase for use across
multiple architectures;
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MARK SCHEME – A Level Computing – COMP2 – June 2015
2 c MAX
6
The role of a translator is to take program
code/source code and to translate it into
a low-level/machine code
A compiler takes the whole source code
and translates it (into machine
code/object code)
Compiled code will execute more quickly
Produces an executable file // no need
for compiler to be distributed with
program // no need to distribute source
code to execute program
An interpreter works
through/translates/recognises program
source code line-by-line
Interpreters call routines built into the
interpreter to execute commands
Interpreting code is slower than running
compiled code
Can run (parts of) a program using an
interpreter even if it contains syntax
errors
Source code is required for the program
to be interpreted // when running
interpreted code the interpreter is always
required
Situations (MAX 1 each for compiler and
interpreter)
Compiler:
So that source code cannot be accessed
by users
When creating an executable file for
distribution
Where speed of execution is important
Where targeting a device with a small
amount of memory
Interpreter:
To allow execution on a wide range of
processors
When prototyping and testing/debugging
code
When no compiler yet exists for the
processor
A. (example of) building a web-application
How to award marks:
Mark Bands and Description
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MARK SCHEME – A Level Computing – COMP2 – June 2015
5- To achieve a mark in this band, candidates
6 must meet the subject criterion (SUB) and all
5 of the quality of written communication
criteria (QWCx).
SUB Candidate has made at least five
mark-worthy points and covers both
interpreter and compiler with a valid
situation for at least one.
QWC1 Text is legible.
QWC2 There are few, if any, errors of
spelling, punctuation and grammar.
Meaning is clear.
QWC3 The candidate has selected and used
a form and style of writing appropriate
to the purpose and has expressed
ideas clearly and fluently.
QWC4 Sentences (and paragraphs) follow
on from one another clearly and
coherently.
QWC5 Appropriate specialist vocabulary has
been used.
3- To achieve a mark in this band, candidates
4 must meet the subject criterion (SUB) and 4 of
the 5 quality of written communication criteria
(QWCx).
SUB Candidate has made at least three
mark-worthy points and covers both
compiler and interpreter.
QWC1 Text is legible.
QWC2 There may be occasional errors of
spelling, punctuation and grammar.
Meaning is clear.
QWC3 The candidate has, in the main, used
a form and style of writing appropriate
to the purpose, with occasional
lapses. The candidate has expressed
ideas clearly and reasonably fluently.
QWC4 The candidate has used well-linked
sentences (and paragraphs).
QWC5 Appropriate specialist vocabulary has
been used.
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MARK SCHEME – A Level Computing – COMP2 – June 2015
1- To achieve a mark in this band, candidates
2 must meet the subject criterion (SUB) and 3 of
the 5 quality of written communication criteria
(QWCx).
SUB Candidate has made a small number
of relevant points.
QWC1 Most of the text is legible.
QWC2 There may be some errors of spelling,
punctuation and grammar but it
should still be possible to understand
most of the response.
QWC3 The candidate has used a form and
style of writing which has many
deficiencies. Ideas are not always
clearly expressed.
QWC4 Sentences (and paragraphs) may not
always be well-connected.
QWC5 Specialist vocabulary has been used
inappropriately or not at all.
0 Candidate has made no relevant points.
Note: Even if English is perfect, candidates can
only get marks for the points made at the top of
the mark scheme for this question.
If a candidate meets the subject criterion in a
band but does not meet the quality of written
communication criteria then drop mark by one
band, providing that at least 4 of the quality of
language criteria are met in the lower band. If 4
criteria are not met then drop by two bands.
3 a 1
Input A Input B Output
0 0 1
0 1 1
1 0 1
1 1 0
One mark for having correct values in Output
column;
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MARK SCHEME – A Level Computing – COMP2 – June 2015
3 b i 3
S A B ̅ ̅ B.S Q
0 0 0 1 0 0 0
0 0 1 1 0 0 0
0 1 0 1 1 0 1
0 1 1 1 1 0 1
1 0 0 0 0 0 0
1 0 1 0 0 1 1
1 1 0 0 0 0 0
1 1 1 0 0 1 1
Marking:
One mark for the ̅ column being correct;
One mark for the B.S column being correct;
The final Q column should follow through from
the previous two columns as an OR statement;
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MARK SCHEME – A Level Computing – COMP2 – June 2015
3 b ii 4
One mark for NOT gate with input from S;
A just a circle on AND gate input from S
One mark for AND gate with input from NOT S
and A; A if no NOT gate from S
One mark for AND gate with input from B and S;
One mark for output from AND gates going into
OR gate with output connect to Q;
3 b iii A multiplexor selects one of several input MAX
lines/wires and forwards/duplicates the Boolean 1
value on this one line onto a single line/wire;
If S is 1 then input B is output otherwise input A
is output // if S is 0 then input A is output
otherwise input B is output;
Note:
1 can be mapped to on/true/high
0 can be mapped to off/false/low
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MARK SCHEME – A Level Computing – COMP2 – June 2015
4 a 1. a mechanical/moveable structure; MAX
2. can sense its surroundings/environment; 2
3. can manipulate things// interact with things;
4. makes dextrous coordinated movements;
5. has some degree of intelligence or ability to
make choices based on environment;
6. is programmable // controlled by a computer
system;
7. a mechanism guided by automatic
controls//autonomous operation;
8. a machine that replaces a human being and
performs various tasks of a human being // can
operate in places/situations humans can not;
9. a device that automatically performs
complicated/repetitive tasks;
10. a mechanism which reacts to its
environment;
11. capable of consistent application/precise
movements;
12. Should obey Asimov's laws // A robot may
not injure a human being // allow a human being
to come to harm;
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MARK SCHEME – A Level Computing – COMP2 – June 2015
4 b MAX
3
The following is a collection of examples that
students could use to support their opinion.
YES:
Programs have been developed to mimic
‘intelligent’ behaviours such as playing chess;
Technology is moving on at a very fast pace;
AI research has shown that computers can
‘learn’;
Research into how the brain works is continuing
to reveal new insights;
Evolutionary algorithms // adaptive algorithms //
computer can modify their own programs;
Computers are getting closer to passing the
Turing test (which is a test for intelligence)
NO:
Computers cannot learn to the same extent as
humans and therefore cannot demonstrate
intelligence;
Computers lack emotion / feelings / instinct /
creativity;
Computers find it hard to cope with unexpected
situations/work well only in a structured
environment;
Hard to actually state/define what intelligence is;
No computer has passed the Turing test (even
though this has been around for a long time) //
due to the Chinese room/box argument;
Theological/existential reasons // intelligence can
only be bestowed by a God;
Note: marks can be awarded for other valid
statements - refer to team leader for discussion
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MARK SCHEME – A Level Computing – COMP2 – June 2015
4 c i a person who breaks through some security 1
systems to gain access to a computer system;
4 c ii Computer Misuse (Act); 1
I. year
4 c iii a global crime as criminals can easily be in MAX
another country; 2
use of botnets means that computers used are
separate from and do not belong to the criminal
// hacking might be routed through multiple
computers // use of public computers/wifi;
use of IP spoofing //changing/dynamic IP
address // use of proxy/vpn;
companies rarely wish to report that they have
been hacked // bad publicity;
often difficult to detect that a crime has been
committed // no physical/biological evidence;
Any other good reason - refer to team leader
if in doubt.
5 a MAX 2 for reader: MAX
RFID reader transmits/sends signal// emits 3
electric / electro-magnetic field;
signal activates/energises/induces current in
RFID tag;
MAX 1 for tag:
RFID tag transmits data (by radio wave);
RFID tag is passive;
5 b Laser Printer - 3; 2
Inkjet Printer - 1;
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MARK SCHEME – A Level Computing – COMP2 – June 2015
5 c To award a mark a comparison between the MAX
two needs to be made. 3
Hard disk drive uses magnetic media, CD-ROM
is an optical media;
Hard disk drive uses magnetic fields, CD-ROM
uses pits (and lands);
Hard disk drive uses magnetic induction (to read
data), CD-ROM uses a laser (and sensor);
Hard disk is split into sectors/tracks, CD-ROM
follows a spiral track;
Hard disk has multiple platters and read/write
heads, CD-ROM single-layered;
Hard disk spins at a fast constant rotation speed,
CD-ROM keeps a constant linear
velocity/speeds rotation up and down;
Hard disk drive is a read/write medium, CD-ROM
is read only;
Hard disk drive and disk are integrated, whereas
drive and disk are separate for CD-ROM;
External hard disk connection via
cable/usb/firewire, CD-ROM requires a CD-ROM
drive;
Hard disk drive can be damaged by exposure to
magnetic field, CD-ROM cannot;
CD-ROM can be scratched, hard disk drive
cannot;
Hard disk drive can transfer/access data faster
than a CD-ROM;
R. portability / lightness / physical size
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MARK SCHEME – A Level Computing – COMP2 – June 2015
6 a </head> MAX
<body> 6
<h1 class="toright">Fairy Cakes</h1>
<hr />
<ol>
<li>Ingredients
<ul>
<li>flour,butter and sugar</li>
<li>2 eggs</li>
</ul>
</li>
<li>Mix together</li>
<li>Bake for 10 minutes</li>
</ol>
<p>Decorate with <span
class="bandw">hundreds and
thousands</span> </p>
</body>
</html>
1 mark – Fairy cakes in a heading tag, <h1>
Fairy Cakes </h1> for example (number can go
up to 7)
1 mark - using class=”toright” to move the Fairy
Cake text [either inside the heading tag or as a
separate div/span]
1 mark – use of <hr> or <hr /> tag for horizontal
rule;
A <p>______________</p>
A a <div> is defined with css to create a margin
or border
1 mark – for the ordered list and correct three
list items
1 mark – for an unordered list being inside the
ordered list and correct two items, unordered list
can be inserted before or after the </li> for
ingredients
DPT if missing end of list tags </ol> and </ul>
1 mark – for correct text ‘Decorate with
hundreds and thousands’ inside <p> and </p>
tags
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MARK SCHEME – A Level Computing – COMP2 – June 2015
1 mark – for the use of <span> and
class=”bandw” to alter text ‘hundreds and
thousands’
[See note below]
1 mark – for the </head><body> </body> and
</html>
No mark for </head> alone
A. either ' ', " " or no quotations around class
selectors
I. missing </li> tags
NOTE:
The student could use an inline tag such as <a>,
<b> or <i> and then apply the class – this should
be awarded the mark. However the <div> or <p>
tag should not be accepted.
6 b Analogous colour scheme: 2
using colours that are adjacent to each other in
the colour wheel;
Complementary colour scheme:
using colours that are opposite to each other in
the colour wheel;
A highly contrasting
7 a SMTP; 2
Telnet; A SSH;
Note
For SMTP accept Simple Mail Transfer Protocol
For SSH accept Secure Shell
7 b Uniform Resource Locator; 1
I case
7 c 129.12.3.236 // 10.0.1.1 // 81.111.110.1 // 1
213.105.114.89 // 62.253.174.77;
I brackets
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MARK SCHEME – A Level Computing – COMP2 – June 2015
7 d A link between routers might be down/busy MAX
and/or a different route is picked; 1
Routes are determined dynamically as the
packet moves from sender to receiver;
A to take the fastest route at that time
NE to travel faster
7 e Layer 2
1 Application (layer)
2 Transport (layer)
3 Network / internet (layer)
4 Link (layer)
1 mark for any two layers correct;
2 marks for all four layers correct;
7 f (Link layer) responsible for network drivers // MAX
network cabling // physical connection // 2
changing from one medium to another;
(Link layer) (removes MAC address and) adds
MAC address for the next hop;
A hardware address for MAC address
(Network layer) looks at destination IP address;
Router decides on next appropriate hop (after
seeing destination IP address);
(Network layer) can split/combine/resize packets
if required;
error checking / error detection;
encryption for wireless connections;
tunnelling through a firewall;
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