Click a paper to view its questions. The specification for the course is shown on the right. For each question, its specification references are listed and can be clicked to scroll the relevant part of the specification into view.
Shade in one lozenge to indicate which of the symbols represents the set of rational numbers.
- A:ℚ
- B:ℝ
- C:ℤ
- D:ℕ
ℚ;
R. more than one lozenge shaded
Shade in one lozenge to indicate which of the symbols represents the set of numbers that does not include all of the numbers -3, 4 and 9.
- A:ℚ
- B:ℝ
- C:ℤ
- D:ℕ
ℕ;
R. more than one lozenge shaded
Shade in one lozenge to indicate which of the symbols represents the set of numbers that is most suitable for measuring the circumference of a ball.
- A:ℚ
- B:ℝ
- C:ℤ
- D:ℕ
ℝ;
R. more than one lozenge shaded
Explain how unsigned binary integers can be converted to hexadecimal. You should illustrate in your explanation how the bit pattern in Figure 1a would be converted.
Mark as follows:
AO1 (understanding) – 1 mark:
The bit pattern is split into 4-bit sections (A. A byte is split in half). Each section is then converted to decimal, with any values above 9 being represented as a letter from A to F / each group of bits is converted to a hexadecimal character;
NE. 4-bits are converted to hexadecimal.
AO2 (apply) – 1 mark:
In the example, the sections are 0001 and 0111. 0001 is 1 in denary, and 0111 is 7 in denary, meaning we are left with the final answer of 17;
If Figure 1a and Figure 1b both represent unsigned binary integers, what is the binary result of adding the two numbers together?
00011101;
I. leading zeroes not given
If Figure 1a and Figure 1b both represent unsigned binary integers, what is the binary result of multiplying the two numbers?
You must show your working.
Figure 1a shifted left by 1: 000101110
Figure 1a shifted left by 2: 0001011100;
Answer: 10001010;
Mark as follows:
1 mark for both correct shifts
1 mark for correct answer
//
2 marks if correct answer and any relevant working shown.
I. leading zeros not given.
A. Alternative method of working.
Indicate clearly on Figure 2 where the binary point must be placed so that the value 19.375 is represented.
Figure 2
1 0 0 1 1 0 1 1
10011.011;
1 mark for fixed point clearly between 5th and 6th digits.
Figure 3 is a 7-bit ASCII character to be transmitted across a network. The system uses odd parity with the parity bit being transmitted in the MSB (Most Significant Bit).
Calculate the parity bit and write it in the empty cell in Figure 3.
Figure 3
? 0 1 0 1 0 1 1
1;
When transmitting data across a network some systems use majority voting rather than a parity bit.
State one advantage of using majority voting over a parity bit and explain how this advantage is achieved.
Majority voting can correct as well as identify errors;
due to the majority bits being taken as the correct value (and discounting/ignoring the minority bit);
//
Majority voting can detect multiple (bit) errors;
as each triplet/odd set of bits represents one bit of data and can identify an error on that bit (not just an error within a byte);
//
Majority voting is more efficient at detecting errors (through multiple bits being corrupted);
as parity bit system may miss errors if an even number of bits are corrupted;
A. points made in reverse, identifying weaknesses of parity bits.
NE. bits are sent multiple times as an explanation
R. implication that receiver knows that the bit is correct
R. data for bit/bits/byte
AO1 (knowledge) – 1 mark:
Identifying an advantage of majority voting over using parity bits.
AO1 (understanding) – 1 mark:
Explaining how the point is an advantage for majority voting.
Must award knowledge mark to award corresponding understanding mark.
The song lasts 3 minutes. The sample resolution is 16 bits and a sample rate of 44 kHz has been used.
A sample rate of 1 Hz means that one sample has been taken every second.
Calculate the minimum amount of storage space, in megabytes (MB), needed to store the song in an uncompressed format.
You must show your working.
Identification of length (180 s/ 3 * 60), sample resolution (16 bit) and sample rate (44,000 Hz) in working ; A. 44 (kHz) for sample rate but do not allow follow through.
Performing the correct calculation (3 * 60 * 16 * 44,000 // 180 * 16 * 44,000) or showing correct intermediary value (126,720,000 bits / 1,584,000 Bytes) ;
I. Conversion
Final answer 15.84(MB) ;
A. to fewer significant places as long as 15.84 can be seen in working.
The song is being recorded using a microphone plugged into the sound card of the computer. The sound card contains an analogue to digital converter (ADC).
Describe the steps the ADC goes through in this process.
The ADC takes samples of the (analogue/continuous electrical) signal (at regular intervals); R. voltage for signal, soundwave, analogue data, sound, waveform for signal.
Samples are quantised // the amplitude/height of each sample is approximated to an integer value // the amplitude/height of samples are measured;
A. voltage for amplitude
A. digital, number, value for integer value
A. explanation of how the signal is quantised
Each sample is assigned a binary value/encoded as a binary value;
R. Digital value for binary value
A. Stored, converted so long as sample is stated
The band have been advised to save their song using lossless compression.
Explain why it might be appropriate for the band to save the song using lossless compression rather than using lossy compression.
Mark as follows:
AO1 (knowledge) – 1 mark:
No/only redundant data is lost during the compression process (if using a lossless format);
Data is lost when storing using a lossy format;
Max 1 mark
AO1 (understanding) – 1 mark:
The song can be reproduced identically to the (recorded) original with no loss of quality (if using a lossless format);
If stored in a lossy format the quality may limit later editing possibilities;
Max 1 mark
A. Recording will be of higher quality / quality of recording will be maintained.
NE. music will be of higher quality.
Explain the differences between an interpreter and a compiler.
A compiler produces object code/machine code/executable file;
An interpreter does not produce any object code;
A compiler translates the whole source code (at once);
An interpreter analyses the code line by line; A. Deals with, translates, processes, R. Runs through, reads, convert
A compiler will not produce an executable file if an error is encountered;
An interpreter will run the program up until the first error;
Interpreted code will execute slower than executing the object code produced by a compiler; A. opposite
You do not need the compiler to execute a compiled program;
When running interpreted code, the interpreter always needs to be present
Once compiled source code is no longer required to run the program;
An interpreter always needs source code at runtime;
Compiled code can only be executed on a machine with the same processor type / instruction set;
Interpreted code is more portable;
Max 3 if all points made about either interpreter or compiler.
A company is using a newly-developed processor in its latest microwave oven. A software developer is writing the program to control the oven.
The developer chose to use assembly language rather than a high-level language to write the program.
Explain why the developer may have made this decision.
| Point | Expansion |
|---|---|
| There may not/probably is not an interpreter/compiler for the chip | as it is bespoke / new |
| As the chip is probably slow (A. low powered) / low in memory | memory space needs to be used efficiently // code needs to be (time) efficient |
| For an interpreted solution the chip would have to incorporate an interpreter | which would increase the memory requirements // restrict the programmer to a specific language |
| Platform dependence is not relevant since | code will only run on one type of device |
| (Translated) assembly language (solution) would (probably) be faster / more efficient | |
| (Translated) assembly language (solution) would (probably) require less memory than high level code | |
| Assembly language (solution) provides for direct control of hardware A. by example | R. registers |
Mark as follows:
1 mark for each point or expansion MAX 3 marks
Point needed for expansion mark to be awarded.
What is the name of the logic gate represented by the truth table and symbol shown in Figure 4?
| A | B | Q |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
NAND;
A. NOT AND
Complete the truth table below to prove that A + B' is equivalent to (A'.B)'.
| A | B |
|---|---|
| 0 | 0 |
| 0 | 1 |
| 1 | 0 |
| 1 | 1 |
| A | B | B̄ | A + B̄ | Ā | Ā · B | (Ā · B)' |
|---|---|---|---|---|---|---|
| 0 | 0 | 1 | 1 | 1 | 0 | 1 |
| 0 | 1 | 0 | 0 | 1 | 1 | 0 |
| 1 | 0 | 1 | 1 | 0 | 0 | 1 |
| 1 | 1 | 0 | 1 | 0 | 0 | 1 |
Mark as follows:
1 mark for column 1 and 3 correct
1 mark for column 4 correct
1 mark for columns 2 and 5 correct and identical
I. order of columns
Using the laws of Boolean algebra, simplify the following Boolean expression:
(X + Y).(X+Y')
You must show your working.
Marking guidance for examiners
- Award marks for working out until an incorrect step has been made.
- If, in any one step, a candidate is simplifying different parts of an expression simultaneously award all relevant marks for this multiple stage but don't award any further marks for working in any parts simplified incorrectly. Example, if the expression P.P.(P+Q) + P.P.1 was changed to P.(P+Q)+P.0, the candidate would get one mark for simplifying the first part to P.(P+Q) and could get further marks for correctly simplifying this part of the expression further but should not be awarded marks for simplifying the incorrectly changed part P.0 (ie to 0)
Mark as follows
1 mark for final answer X
Max 3 marks for working:
- 1 mark for each application of an identity other than cancelling NOTs that produces a simpler expression.
- 1 mark for expanding brackets
- 1 mark for putting an expression into brackets that would lead to a simpler expression.
Note: a simpler expression is one that is logically equivalent to the original expression but uses fewer logical operators.
Max 3 if answer is correct but any incorrect working or significant steps of working is missing.
Example working (1)
X. X + X. Ȳ + Y. X + Y. Ȳ
X + X. Ȳ + Y. X + 0
X(1 + Ȳ + Y) or X + X(Ȳ + Y)
[expansion of brackets]
[use of X ∙ X = X and Y. Ȳ = 0]
[taking X outside of brackets]
Alternative example working (2)
X + (Y. Ȳ)
X + 0
X
[Use of distributive law]
[Y. Ȳ = 0]
[Recognising X+0 = X]
Describe one difference between the way the Harvard and von Neumann architectures operate.
Harvard uses separate memory/bus/address space // von Neumann uses combined memory/bus/address space; for instructions/program and data;
NE. Places, locations, registers, areas of memory
A. Main memory
NOTE: It must be clear that instructions/data are stored in separate memory, not separately in memory.
Shade one lozenge to indicate the type of computer architecture that is typically used for digital signal processing.
- A:Harvard
- B:von Neumann
Harvard;
R. more than one lozenge shaded
Describe, using full sentences, the steps involved in the Fetch-Execute cycle for the von Neumann architecture. Your description should cover the fetch, decode and execute stages and must clearly state which of the three sections each step falls in.
Level of response question
| Level | Description | Mark Range |
|---|---|---|
| 3 | At least five of the steps of the cycle have been correctly identified in order/the steps are all in correct order and covering all three of the stages (fetch, decode, execute). For the top mark in this level thorough understanding of how the cycle works is evident. | 5-6 |
| 2 | At least three steps of the cycle have been identified in order, covering at least two of the stages (fetch, decode, execute). Some understanding of how the cycle works is evident. | 3-4 |
| 1 | At least one step of the cycle have been identified, covering at least one stage (fetch, decode or execute). The order of the steps may not be correct. Little understanding of how the cycle works is evident. | 1-2 |
Points may include:
Fetch:
- Contents of Program Counter / PC transferred to Memory Address Register / MAR
- Address bus used to transfer this address to main memory
- Transfer of content uses the data bus
- Contents of addressed memory location loaded into the Memory Buffer Register / MBR
- Increment (contents of) Program Counter / PC A. at any part of fetch process after transferring PC to MAR
- Increment Program Counter / PC and fetch simultaneously
- Contents of MBR copied to CIR
Decode:
- Decode instruction held by the (Current) Instruction Register / (C)IR
- The control unit decodes the instruction
- Instruction split into opcode and operand
Execute:
- If necessary, data is fetched
- If necessary, data is stored in memory
- The opcode identifies the type of operation/instruction to be performed (by the processor)
- Result (may be) stored in register/accumulator
- The operation (identified by the opcode) is performed by the processor. A. ALU
- Status register updated
- If jump / branch required Program Counter/PC is updated
NE. Register notation
A. Memory Data Register/MDR for Memory Buffer Register/MBR
I. Incorrect headings
Figure 5 shows an incomplete assembly language program. The intended purpose of the code is to count from 1 to 10 inclusive, writing the values to memory location 17, which is used to control a motor.
Complete the code in Figure 5. You may not need to use all four lines for your solution and you should not write more than one instruction per line.
Figure 5
MOV R0, #1
startloop:
STR R0, 17
_______________________
_______________________
_______________________
_______________________
endloop:
HALT
Answer 1
- ADD R0, R0, #1 ;
- CMP R0, #11 ;
- BNE; startloop ;
Answer 2
- ADD R0, R0, #1 ;
- CMP R0, #11 ;
- BEQ endloop ;
- B startloop ;
Answer 3
- CMP R0, #10 ;
- BEQ endloop ;
- ADD R0, R0, #1 ;
- B startloop ;
Answer 4
- ADD R0, R0, #1 ;
- CMP R0, #11 ;
- BLT; startloop ;
Stop marking when the first incorrect command is encountered. Mark response against whichever alternative gives the highest mark.
I. Any extra commands which do not effect operation of program.
R1 contains the decimal value 7. What value will be contained in R1 after the instruction below is executed?
LSL R1, R1, #2
2810 // (000)111002;
TO. If two answers given and one is incorrect.
I. Lack of subscript.
Explain the difference between direct addressing and immediate addressing.
Direct addressing means that the operand is the (memory) address/register number (of the datum) whereas immediate addressing means the operand is the datum ;
Note: Must be clear that the operand is being used.
Describe two reasons why serial transmission might be preferred to parallel transmission.
- Parallel communication requires more wires (and hardware);
- Higher cost
- More difficult to manage when setting up the system
- More difficult to repeat/switch
- Parallel communication needs the data to be kept synchronised across wires / risk of data skew over long distances;
- More chance of errors
- Limiting factor on transmission speed (as problem worsens at higher speeds)
- Limiting factor on cable length
- Parallel communication carries the risk of crosstalk between wires;
- More chance of errors
- Limiting factor on transmission speed (as problem worsens at higher speeds)
2 marks for AO1 (knowledge) for making any two of points 1,2,3 above – 1 mark per point.
2 marks for AO1 (understanding) for making any of the bulleted points above and linking the points to an associated knowledge point – 1 mark per point. Note that only 1 mark can be awarded for a particular understanding point (e.g more chance of errors) even if it is made more than once and connected to different knowledge points.
A. points made in reverse, for example serial communication has less chance of errors because it uses fewer wires so cross talk does not occur.
In the context of networking, define the following terms.
Bit rate:
Latency:
1 mark for each term defined
[Bit rate] The number of bits that can be sent/received/transferred in one second/unit of time // the frequency at which bits can be transmitted/transferred;
R. Unexplained examples
[Latency] The delay between an action being instigated and its effect being noticed;
A. time delay between signal being transmitted and arriving
A. time taken for transmitted data to arrive at the receiver
A. lag for time delay
NE. delay in transmission, transmission time
Explain how disabling SSID (Service Set Identifier) broadcasting can increase the security of a wireless network.
The SSID/Service Set Identifier of the network will not be visible when trying to connect to a network; this means that only users who know the SSID of the network can try to connect;
A. name for SSID
Explain how the use of a MAC (Media Access Control) address white list can increase the security of a wireless network.
A MAC/Media Access Control address is unique to every NIC/Network Interface Card;
A white list only allows those MAC addresses that have been authorised to connect to the network // devices whose MAC addresses are not in the white list are not allowed to connect to the network;
A. Device for NIC
A. Address for MAC Address
R. first mark if not clear that MAC address is unique to NIC/device
R. IP address for MAC address
Google have a service called Street View which allows a user to view surroundings from street-level. Google have extended their Street View service to cover the inside of buildings such as museums and sports stadiums.
Discuss a range of ethical, legal and cultural issues that Google may have needed to deal with when extending the service.
Level of response question
| Level | Description | Mark Range |
|---|---|---|
| 3 | A line of reasoning has been followed to produce a coherent, relevant, substantiated and logically structured response. The response covers ethical, legal and cultural issues. In these areas, there is sufficient detail to show that the student has a thorough level of understanding of the issues involved. Although understanding would be indicated by two or three points being made in each of the areas, although potentially thorough coverage of two areas might exceptionally lead to a mark in this band. | 7-9 |
| 2 | A line of reasoning has been followed to produce a mostly coherent, relevant, substantiated and logically structured response that covers at least two of ethical, legal and cultural issues. In at least one of these areas, at least two valid points must have been made that demonstrates a good understanding, and typically students should have made at least two points in two areas. | 4-6 |
| 1 | A few relevant points have been made and there is limited evidence that a line of reasoning has been followed. | 1-3 |
Points may include:
Ethical:
- Consider if material in images could be of harm to children
- Identifying and requesting permission from any members of public caught on the images.
- Members of the public may not be as happy being photographed in a building as they are on the streets.
- Recording of adverts could lead to unfair product placement
- Considering what harmful uses users of the system might use the captured images for.
- Considering how often Google should update the image data.
- Dealing with copyrighted information that might have been inadvertently captured.
- Considering that access via Street View might reduce the number of paying customers for museums.
- Are young people being dissuaded from leaving home to visit public buildings leading to poor health.
- Need to consider which areas of a building are appropriate to film (eg toilets, offices, research laboratories)
Legal:
- Does Google need permission to film in what might be a private building.
- It may not be legal to film people without permission (on private land).
- Aspects of data protection legislation might apply.
- Copyrighted information might be inadvertently captured and may lead to legislation breach.
- Consider if material in images is legally allowed to be viewed by children.
- Could be a risk of identifying items to steal leading to liability for crimes being carried out.
- Ability to identify locations and access could be used for crime or to carry out acts of terrorism.
- Street View is a worldwide service so would need to consider different legal systems.
- Consideration to the security of information storage needs to be made.
- Laws for certain buildings or areas of buildings may be more restrictive than others.
Cultural:
- Some images of people or exhibits may be offensive to certain cultures.
- Taking images inside religious buildings for some purposes may be considered inappropriate.
- Some cultural beliefs may not allow photography of people.
- Do people have the right to request the deletion of their images?
- Could the culture of visiting places such as museums (e.g. family/school day trips) be affected by access them online?
- Need for balance between cultural sensitivities and freedom of expression.
NE. Without suitable context: Faces need to be blurred out, must comply with laws, invasion of privacy.
R. Reference to private homes, implication that will be used for live monitoring.
A laser printer has a representation of an image stored in its memory.
Describe how it prints this image on to a piece of paper.
Level of response question
| Level | Description | Mark Range |
|---|---|---|
| 3 | At least five points have been made showing knowledge of five steps in the process. The description shows a thorough level of understanding and all of the steps have been correctly sequenced. | 5-6 |
| 2 | At least three points have been made showing knowledge of three steps in the process. Good, mostly correct understanding of the process is demonstrated between 3 or more steps. | 3-4 |
| 1 | At least one point has been made showing knowledge of one step in the process. Some understanding may be shown if two steps are covered and correctly sequenced. | 1-2 |
Points may include:
- Print drum coated in (positive static) charge
- Printer generates bitmap of page from the data
- Laser beams shone / directed at / draws on print drum
- Via rotating (octagonal) mirror
- Laser is modulated (turned on & off)
- Laser removes / neutralises / reverses electric charge on drum where image should be dark / black
- Toner is given (positive) charge
- Charged drum picks up toner
- For drum/laser mechanisms, one for each colour (cyan etc)
- Toner transferred (from drum) to paper / paper rolled over drum (to transfer toner)
- Toner is fused / bonded / melted / stuck to paper (by heated rollers / pressure) (must be clear that toner is already on paper when it is fused, not still on drum)
A. Reversal or lack of polarity of static charge.
Paper 2 covers sections 5-9 of the AQA AS Computer Science specification.
5 Fundamentals of data representation
5.1 Number systems
5.1.1 Natural numbers
| Reference | Content | Additional information |
|---|---|---|
| 5.1.1.1 View | Be familiar with the concept of a natural number and the set ℕ of natural numbers (including zero). | ℕ = {0, 1, 2, 3, …} |
5.1.2 Integer numbers
| Reference | Content | Additional information |
|---|---|---|
| 5.1.2.1 View | Be familiar with the concept of an integer and the set ℤ of integers. | ℤ = { …, -3, -2, -1, 0, 1, 2, 3, … } |
5.1.3 Rational numbers
| Reference | Content | Additional information |
|---|---|---|
| 5.1.3.1 View | Be familiar with the concept of a rational number and the set ℚ of rational numbers, and that this set includes the integers. | ℚ is the set of numbers that can be written as fractions (ratios of integers). Since a number such as 7 can be written as 7/1, all integers are rational numbers. |
5.1.4 Irrational numbers
| Reference | Content | Additional information |
|---|---|---|
| 5.1.4.1 View | Be familiar with the concept of an irrational number. | An irrational number is one that cannot be written as a fraction, for example √2. |
5.1.5 Real numbers
| Reference | Content | Additional information |
|---|---|---|
| 5.1.5.1 View | Be familiar with the concept of a real number and the set ℝ of real numbers, which includes the natural numbers, the rational numbers, and the irrational numbers. | ℝ is the set of all 'possible real world quantities'. |
5.1.6 Ordinal numbers
| Reference | Content | Additional information |
|---|---|---|
| 5.1.6.1 View | Be familiar with the concept of ordinal numbers and their use to describe the numerical positions of objects. | When objects are placed in order, ordinal numbers are used to tell their position. For example, if we have a well-ordered set S = {'a', 'b', 'c', 'd'}, then 'a' is the 1st object, 'b' the 2nd, and so on. |
5.1.7 Counting and measurement
| Reference | Content | Additional information |
|---|---|---|
| 5.1.7.1 View | Be familiar with the use of natural numbers for counting. | |
| 5.1.7.2 View | Be familiar with the use of real numbers for measurement. |
5.2 Number bases
5.2.1 Number base
| Reference | Content | Additional information |
|---|---|---|
| 5.2.1.1 View | Be familiar with the concept of a number base, in particular:
| Students should be familiar with expressing a number's base using a subscript as follows:
|
| 5.2.1.2 View | Convert between decimal, binary and hexadecimal number bases. | |
| 5.2.1.3 View | Be familiar with, and able to use, hexadecimal as a shorthand for binary and to understand why it is used in this way. |
5.3 Units of information
5.3.1 Bits and bytes
| Reference | Content | Additional information |
|---|---|---|
| 5.3.1.1 View | Know that the bit is the fundamental unit of information. | A bit is either 0 or 1. |
| 5.3.1.2 View | Know that a byte is a group of 8 bits. | |
| 5.3.1.3 View | Know that 2n different values can be represented with n bits. | For example, 3 bits can be configured in 23 = 8 different ways: 000, 001, 010, 011, 100, 101, 110, 111. |
5.3.2 Units
| Reference | Content | Additional information |
|---|---|---|
| 5.3.2.1 View | Know the names, symbols and corresponding powers of 10 for the decimal prefixes:
| |
| 5.3.2.2 View | Know the names, symbols and corresponding powers of 2 for the binary prefixes:
| |
| 5.3.2.3 View | Know that quantities of bytes can be described using binary prefixes representing powers of 2 or using decimal prefixes representing powers of 10, eg one kibibyte is written as 1KiB = 210 B and one kilobyte is written as 1 kB = 103 B. | Historically the terms kilobyte, megabyte, etc have often been used when kibibyte, mebibyte, etc are meant. |
5.4 Binary number system
5.4.1 Unsigned binary
| Reference | Content | Additional information |
|---|---|---|
| 5.4.1.1 View | Know the difference between unsigned binary and signed binary. | Students are expected to be able to convert between unsigned binary and decimal and vice versa. |
| 5.4.1.2 View | Know that in unsigned binary the minimum and maximum values for a given number of bits, n, are 0 and 2n - 1 respectively. |
5.4.2 Unsigned binary arithmetic
| Reference | Content | Additional information |
|---|---|---|
| 5.4.2.1 View | Be able to add two unsigned binary integers. | |
| 5.4.2.2 View | Be able to multiply two unsigned binary integers. |
5.4.3 Signed binary using two's complement
| Reference | Content | Additional information |
|---|---|---|
| 5.4.3.1 View | Know that signed binary can be used to represent negative integers and that one possible coding scheme is two's complement. | This is the only representation of negative integers that will be examined. Students are expected to be able to convert between signed binary and decimal and vice versa. |
| 5.4.3.2 View | Know how to represent negative and positive integers in two's complement. | |
| 5.4.3.3 View | Know how to perform subtraction using two's complement. | |
| 5.4.3.4 View | Know how to calculate the range of a given number of bits, n. |
5.4.4 Numbers with a fractional part
| Reference | Content | Additional information |
|---|---|---|
| 5.4.4.1 View | Know how numbers with a fractional part can be represented in fixed point form in binary in a given number of bits. | |
| 5.4.4.2 View | Be able to convert decimal to fixed point binary of a given number of bits. | |
| 5.4.4.3 View | Be able to convert fixed point binary to decimal of a given number of bits. |
5.5 Information coding systems
5.5.1 Character form of a decimal digit
| Reference | Content | Additional information |
|---|---|---|
| 5.5.1.1 View | Differentiate between the character code representation of a decimal digit and its pure binary representation. |
5.5.2 ASCII and Unicode
| Reference | Content | Additional information |
|---|---|---|
| 5.5.2.1 View | Describe ASCII and Unicode coding systems for coding character data. | |
| 5.5.2.2 View | Explain why Unicode was introduced. |
5.5.3 Error checking and correction
| Reference | Content | Additional information |
|---|---|---|
| 5.5.3.1 View | Describe and explain the use of parity bits. | |
| 5.5.3.2 View | Describe and explain the use of majority voting. | |
| 5.5.3.3 View | Describe and explain the use of check digits. | |
| 5.5.3.4 View | Evaluate the use of parity bits, majority voting and check digits |
5.6 Representing images, sound and other data
5.6.1 Bit patterns, images, sound and other data
| Reference | Content | Additional information |
|---|---|---|
| 5.6.1.1 View | Describe how bit patterns may represent other forms of data, including graphics and sound. |
5.6.2 Analogue and digital
| Reference | Content | Additional information |
|---|---|---|
| 5.6.2.1 View | Understand the difference between analogue and digital:
|
5.6.3 Analogue/digital conversion
| Reference | Content | Additional information |
|---|---|---|
| 5.6.3.1 View | Describe the principles of operation of an analogue to digital converter (ADC). | |
| 5.6.3.2 View | Describe the principles of operation of a digital to analogue converter (DAC). |
5.6.4 Bitmapped graphics
| Reference | Content | Additional information |
|---|---|---|
| 5.6.4.1 View | Explain how bitmaps are represented. | |
| 5.6.4.2 View | Explain resolution. | Resolution is expressed as number of dots per inch where a dot is a pixel. |
| 5.6.4.3 View | Know that colour depth is the number of bits stored for each pixel. | |
| 5.6.4.4 View | Know that the size of an image in pixels is width of image in pixels × height of image in pixels. | The size of an image is also alternatively sometimes described as the resolution of an image. |
| 5.6.4.5 View | Calculate storage requirements for bitmapped images and be aware that bitmap image files may also contain metadata. | Ignoring metadata, storage requirements = size in pixels x colour depth where size in pixels is width in pixels x height in pixels. |
| 5.6.4.6 View | Be familiar with typical metadata. | eg width, height, colour depth. |
5.6.5 Digital representation of sound
| Reference | Content | Additional information |
|---|---|---|
| 5.6.5.1 View | Describe the digital representation of sound. | |
| 5.6.5.2 View | Understand sample resolution and its effect on the quality of audio recordings. | |
| 5.6.5.3 View | Understand sampling rate and its effect on the quality of audio recordings. | |
| 5.6.5.4 View | Know Nyquist's theorem. | |
| 5.6.5.5 View | Calculate sound sample sizes in bytes. |
5.6.6 Musical Instrument Digital Interface (MIDI)
| Reference | Content | Additional information |
|---|---|---|
| 5.6.6.1 View | Describe the purpose of MIDI and the use of event messages in MIDI. | |
| 5.6.6.2 View | Describe the advantages of using MIDI files for representing music. |
5.6.7 Data compression
| Reference | Content | Additional information |
|---|---|---|
| 5.6.7.1 View | Know why images and sound files are often compressed and that other files, such as text files, can also be compressed. | |
| 5.6.7.2 View | Understand the difference between lossless and lossy compression and explain the advantages and disadvantages of each. | |
| 5.6.7.3 View | Explain the principles behind run length encoding (RLE) for lossless compression. | |
| 5.6.7.4 View | Explain the principles behind dictionary-based methods for lossless compression. |
5.6.8 Encryption
| Reference | Content | Additional information |
|---|---|---|
| 5.6.8.1 View | Understand what is meant by encryption and be able to define it. | Caesar and Vernam ciphers are at opposite extremes. One offers perfect security, the other doesn't. Between these two types are ciphers that are computationally secure – see below. Students will be assessed on the two types. Ciphers other than Caesar may be used to assess students' understanding of the principles involved. These will be explained and be similar in terms of computational complexity. |
| 5.6.8.2 View | Be familiar with the term cipher. | |
| 5.6.8.3 View | Be familiar with the term plaintext. | |
| 5.6.8.4 View | Be familiar with the term ciphertext. | |
| 5.6.8.5 View | Be familiar with Caesar cipher and be able to apply it to encrypt a plaintext message and decrypt a ciphertext. | |
| 5.6.8.6 View | Be able to explain why Caesar cipher is easily cracked. | |
| 5.6.8.7 View | Be familiar with Vernam cipher or one-time pad and be able to apply it to encrypt a plaintext message and decrypt a ciphertext. | Since the key k is chosen uniformly at random, the ciphertext c is also distributed uniformly. The key k must be used once only. The key k is known as a one-time pad. |
| 5.6.8.8 View | Explain why Vernam cipher is considered as a cypher with perfect security. | |
| 5.6.8.9 View | Compare Vernam cipher with ciphers that depend on computational security. | Vernam cipher is the only one to have been mathematically proved to be completely secure. The worth of all other ciphers ever devised is based on computational security. In theory, every cryptographic algorithm except for Vernam cipher can be broken, given enough ciphertext and time. |
6 Fundamentals of computer systems
6.1 Hardware and software
6.1.1 Relationship between hardware and software
| Reference | Content | Additional information |
|---|---|---|
| 6.1.1.1 View | Define the term hardware. | |
| 6.1.1.2 View | Define the term software. | |
| 6.1.1.3 View | Understand the relationship between hardware and software. |
6.1.2 Classification of software
| Reference | Content | Additional information |
|---|---|---|
| 6.1.2.1 View | Explain what is meant by system software. | |
| 6.1.2.2 View | Explain what is meant by application software. | |
| 6.1.2.3 View | Understand the need for, and attributes of, different types of software. |
6.1.3 System software
| Reference | Content | Additional information |
|---|---|---|
| 6.1.3.1 View | Know that system software includes operating systems (OSs), utility programs, libraries and translators (compiler, assembler, interpreter). | |
| 6.1.3.2 View | Understand the need for, and functions of operating systems (OSs). | |
| 6.1.3.3 View | Understand the need for, and functions of utility programs. | |
| 6.1.3.4 View | Understand the need for, and functions of libraries. | |
| 6.1.3.5 View | Understand the need for, and functions of translators (compiler, assembler, interpreter). |
6.1.4 Role of an operating system (OS)
| Reference | Content | Additional information |
|---|---|---|
| 6.1.4.1 View | Understand that a role of the operating system is to hide the complexities of the hardware. | |
| 6.1.4.2 View | Know that the OS handles resource management, managing hardware to allocate processors, memories and I/O devices among competing processes. |
6.2 Classification of programming languages
6.2.1 Classification of programming languages
| Reference | Content | Additional information |
|---|---|---|
| 6.2.1.1 View | Show awareness of the development of types of programming languages and their classification into low- and high-level languages. | |
| 6.2.1.2 View | Know that low-level languages are considered to be:
| |
| 6.2.1.3 View | Know that high-level languages include imperative high-level language. | |
| 6.2.1.4 View | Describe machine-code language and assembly language. | |
| 6.2.1.5 View | Understand the advantages and disadvantages of machine-code and assembly language programming compared with high-level language programming. | |
| 6.2.1.6 View | Explain the term 'imperative high-level language' and its relationship to low-level languages. |
6.3 Types of program translator
6.3.1 Types of program translator
| Reference | Content | Additional information |
|---|---|---|
| 6.3.1.1 View | Understand the role of assemblers. | |
| 6.3.1.2 View | Understand the role of compilers. | |
| 6.3.1.3 View | Understand the role of interpreters. | |
| 6.3.1.4 View | Explain the differences between compilation and interpretation. Describe situations in which each would be appropriate. | |
| 6.3.1.5 View | Explain why an intermediate language such as bytecode is produced as the final output by some compilers and how it is subsequently used. | |
| 6.3.1.6 View | Understand the difference between source and object (executable) code. |
6.4 Logic gates
6.4.1 Logic gates
| Reference | Content | Additional information |
|---|---|---|
| 6.4.1.1 View | Construct truth tables for the NOT logic gate. | Students should know and be able to use ANSI/IEEE standard 91-1984 Distinctive shape logic gate symbols for these logic gates. |
| 6.4.1.2 View | Construct truth tables for the AND logic gate. | |
| 6.4.1.3 View | Construct truth tables for the OR logic gate. | |
| 6.4.1.4 View | Construct truth tables for the XOR logic gate. | |
| 6.4.1.5 View | Construct truth tables for the NAND logic gate. | |
| 6.4.1.6 View | Construct truth tables for the NOR logic gate. | |
| 6.4.1.7 View | Be familiar with drawing and interpreting logic gate circuit diagrams involving one or more of the above gates. | |
| 6.4.1.8 View | Complete a truth table for a given logic gate circuit. | |
| 6.4.1.9 View | Write a Boolean expression for a given logic gate circuit. | |
| 6.4.1.10 View | Draw an equivalent logic gate circuit for a given Boolean expression. |
6.5 Boolean algebra
6.5.1 Using Boolean algebra
| Reference | Content | Additional information |
|---|---|---|
| 6.5.1.1 View | Be familiar with the use of Boolean identities and De Morgan's laws to manipulate and simplify Boolean expressions. |
7 Fundamentals of computer organisation and architecture
7.1 Internal hardware components of a computer
7.1.1 Internal hardware components of a computer
| Reference | Content | Additional information |
|---|---|---|
| 7.1.1.1 View | Have an understanding and knowledge of the basic internal components of a computer system. | Although exam questions about specific machines will not be asked, it might be useful to base this section on the machines used at the centre. |
| 7.1.1.2 View | Understand the role of the processor. | |
| 7.1.1.3 View | Understand the role of main memory. | |
| 7.1.1.4 View | Understand the role of the address bus. | |
| 7.1.1.5 View | Understand the role of the data bus. | |
| 7.1.1.6 View | Understand the role of the control bus. | |
| 7.1.1.7 View | Understand the role of I/O controllers. | |
| 7.1.1.8 View | Be able to explain the difference between von Neumann and Harvard architectures and describe where each is typically used. | Embedded systems such as digital signal processing (DSP) systems use Harvard architecture processors extensively. Von Neumann architecture is used extensively in general purpose computing systems. |
| 7.1.1.9 View | Understand the concept of addressable memory. |
7.2 The stored program concept
7.2.1 The meaning of the stored program concept
| Reference | Content | Additional information |
|---|---|---|
| 7.2.1.1 View | Be able to describe the stored program concept: machine code instructions stored in main memory are fetched and executed serially by a processor that performs arithmetic and logical operations. |
7.3 Structure and role of the processor and its components
7.3.1 The processor and its components
| Reference | Content | Additional information |
|---|---|---|
| 7.3.1.1 View | Explain the role and operation of the arithmetic logic unit. | |
| 7.3.1.2 View | Explain the role and operation of the control unit. | |
| 7.3.1.3 View | Explain the role and operation of the clock. | |
| 7.3.1.4 View | Explain the role and operation of general-purpose registers. | |
| 7.3.1.5 View | Explain the role and operation of the program counter. | |
| 7.3.1.6 View | Explain the role and operation of the current instruction register. | |
| 7.3.1.7 View | Explain the role and operation of the memory address register. | |
| 7.3.1.8 View | Explain the role and operation of the memory buffer register. | |
| 7.3.1.9 View | Explain the role and operation of the status register. |
7.3.2 The Fetch-Execute cycle and the role of registers within it
| Reference | Content | Additional information |
|---|---|---|
| 7.3.2.1 View | Explain how the Fetch-Execute cycle is used to execute machine code programs, including the stages in the cycle (fetch, decode, execute) and details of registers used. |
7.3.3 The processor instruction set
| Reference | Content | Additional information | |||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 7.3.3.1 View | Understand the term 'processor instruction set' and know that an instruction set is processor specific. | ||||||||||||||||||
| 7.3.3.2 View | Know that instructions consist of an opcode and one or more operands (value, memory address or register). | A simple model will be used in which the addressing mode will be incorporated into the bits allocated to the opcode so the latter defines both the basic machine operation and the addressing mode. Students will not be expected to define opcode, only interpret opcodes in the given context of a question. For example, 4 bits have been allocated to the opcode (3 bits for basic machine operation, eg ADD, and 1 bit for the addressing mode). 4 bits have been allocated to the operand, making the instruction, opcode + operand, 8 bits in length. In this example, 16 different opcodes are possible (24 = 16).
| |||||||||||||||||
7.3.4 Addressing modes
| Reference | Content | Additional information |
|---|---|---|
| 7.3.4.1 View | Understand and apply immediate addressing. | Immediate addressing: the operand is the datum. |
| 7.3.4.2 View | Understand and apply direct addressing. | Direct addressing: the operand is the address of the datum. Address to be interpreted as meaning either main memory or register. |
7.3.5 Machine-code/assembly language operations
| Reference | Content | Additional information |
|---|---|---|
| 7.3.5.1 View | Understand and apply the basic machine-code operations of:
Use the basic machine-code operations above when machine-code instructions are expressed in mnemonic form—assembly language, using immediate and direct addressing. |
7.3.6 Factors affecting processor performance
| Reference | Content | Additional information |
|---|---|---|
| 7.3.6.1 View | Explain the effect on processor performance of multiple cores. | |
| 7.3.6.2 View | Explain the effect on processor performance of cache memory. | |
| 7.3.6.3 View | Explain the effect on processor performance of clock speed. | |
| 7.3.6.4 View | Explain the effect on processor performance of word length. | |
| 7.3.6.5 View | Explain the effect on processor performance of address bus width. | |
| 7.3.6.6 View | Explain the effect on processor performance of data bus width. |
7.4 External hardware devices
7.4.1 Input and output devices
| Reference | Content | Additional information |
|---|---|---|
| 7.4.1.1 View | Know the main characteristics, purpose and suitability of barcode readers and understand their principles of operation. | |
| 7.4.1.2 View | Know the main characteristics, purpose and suitability of digital cameras and understand their principles of operation. | |
| 7.4.1.3 View | Know the main characteristics, purpose and suitability of laser printers and understand their principles of operation. | |
| 7.4.1.4 View | Know the main characteristics, purpose and suitability of RFID and understand their principles of operation. |
7.4.2 Secondary storage devices
| Reference | Content | Additional information |
|---|---|---|
| 7.4.2.1 View | Explain the need for secondary storage within a computer system. | |
| 7.4.2.2 View | Know the main characteristics, purposes, suitability and understand the principles of operation of the hard disk. | |
| 7.4.2.3 View | Know the main characteristics, purposes, suitability and understand the principles of operation of the optical disk. | |
| 7.4.2.4 View | Know the main characteristics, purposes, suitability and understand the principles of operation of the solid-state disk (SSD). | SSD = NAND flash memory + a controller that manages pages, and blocks and complexities of writing. Based on floating gate transistors that trap and store charge. A block, made up of many pages, cannot overwrite pages; a page has to be erased before it can be written to but technology requires the whole block to be erased. Lower latency and faster transfer speeds than a magnetic disk drive. |
| 7.4.2.5 View | Compare the capacity and speed of access of various media and make a judgement about their suitability for different applications. |
8 Consequences of uses of computing
8.1 Individual (moral), social (ethical), legal and cultural issues and opportunities
| Reference | Content | Additional information |
|---|---|---|
| 8.1.1 View | Show awareness of current individual (moral), social (ethical), legal and cultural opportunities and risks of computing. Understand that:
Be able to discuss the challenges facing legislators in the digital age. | Teachers may wish to employ two very powerful techniques, hypotheticals and case studies, to engage students in the issues. Hypotheticals allow students to isolate quickly important ethical principles in an artificially simplified context. For example, a teacher might ask students to explain and defend how, as a Google project manager, they would evaluate a proposal to bring Google's Street View technology to a remote African village. What questions should be asked? Who should be consulted? What benefits, risks and safeguards considered? What are the trade-offs? Case studies allow students to confront the tricky interplay between the sometimes competing ethical values and principles relevant in real world settings. For example, the Google Street View case might be used to tease out the ethical conflicts between individual and cultural expectations, the principle of informed consent, Street View's value as a service, its potential impact on human perceptions and behaviours, and its commercial value to Google and its shareholders. There are many resources available on the Internet to support teaching of this topic. |
9 Fundamentals of communication and networking
9.1 Communication
9.1.1 Communication methods
| Reference | Content | Additional information |
|---|---|---|
| 9.1.1.1 View | Define serial transmission methods. | |
| 9.1.1.2 View | Define parallel transmission methods. | |
| 9.1.1.3 View | Discuss the advantages of serial over parallel transmission. | |
| 9.1.1.4 View | Define and compare synchronous and asynchronous data transmission. | |
| 9.1.1.5 View | Describe the purpose of start and stop bits in asynchronous data transmission. |
9.1.2 Communication basics
| Reference | Content | Additional information |
|---|---|---|
| 9.1.2.1 View | Define baud rate. | |
| 9.1.2.2 View | Define bit rate. | |
| 9.1.2.3 View | Define bandwidth. | |
| 9.1.2.4 View | Define latency. | |
| 9.1.2.5 View | Define protocol. | |
| 9.1.2.6 View | Differentiate between baud rate and bit rate. | Bit rate can be higher than baud rate if more than one bit is encoded in each signal change. |
| 9.1.2.7 View | Understand the relationship between bit rate and bandwidth. | Bit rate is directly proportionate to bandwidth. |
9.2 Networking
9.2.1 Network topology
| Reference | Content | Additional information |
|---|---|---|
| 9.2.1.1 View | Understand and explain the operation of a physical star topology. | |
| 9.2.1.2 View | Understand and explain the operation of a logical bus network topology. | A network physically wired in star topology can behave logically as a bus network by using a bus protocol and appropriate physical switching. |
| 9.2.1.3 View | Differentiate between the physical star topology and the logical bus network topology. |
9.2.2 Types of networking between hosts
| Reference | Content | Additional information |
|---|---|---|
| 9.2.2.1 View | Explain peer-to-peer networking and describe situations where it might be used. | In a peer-to-peer network, each computer has equal status. |
| 9.2.2.2 View | Explain client-server networking and describe situations where it might be used. | In a client-server network, most computers are nominated as clients and one or more as servers. The clients request services from the servers, which provide these services, for example file server, email server. |
9.2.3 Wireless networking
| Reference | Content | Additional information |
|---|---|---|
| 9.2.3.1 View | Explain the purpose of WiFi. | A wireless local area network that is based on international standards. Used to enable devices to connect to a network wirelessly. |
| 9.2.3.2 View | Be familiar with the components required for wireless networking. |
|
| 9.2.3.3 View | Be familiar with the purpose of Service Set Identifier (SSID). | |
| 9.2.3.4 View | Be familiar with how wireless networks are secured using WPA (Wifi Protected Access)/WPA2. | |
| 9.2.3.5 View | Be familiar with how wireless networks are secured by disabling SSID (Service Set Identifier) broadcasting. | |
| 9.2.3.6 View | Be familiar with how wireless networks are secured using a MAC (Media Access Control) address allow list. | |
| 9.2.3.7 View | Explain the wireless protocol Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) with and without Request to Send/Clear to Send (RTS/CTS). |