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.
Describe the set of real numbers.
All possible real-world quantities/values/numbers;
(Includes) the rational and irrational numbers (and the integers and natural numbers);
A value that represents any quantity along the number line;
A. All numbers excluding imaginary/complex numbers.
The number 5 can be written as 15/3
Shade two lozenges to indicate which of the following statements are true.
- A 15 and 3 are not integers
- B 15 and 3 are irrational numbers
- C 5 is an irrational number
- D 5 is a natural number
- E 5 is a rational number
- D (5 is a natural number);
- E (5 is a rational number);
- R. more than two lozenges shaded
Shade one lozenge to indicate which of the symbols below represents the set of rational numbers.
- A ℂ
- B ℕ
- C ℚ
- D ℝ
- E ℤ
C (ℚ);
R. more than one lozenge shaded
Convert the bit pattern 10001010 to hexadecimal.
8A;
Represent the decimal number 139 as an 8-bit unsigned binary integer.
1000 1011;
Show how the unsigned binary number 00100011 can be added to the unsigned binary number 00101011 without converting the numbers into decimal.
You must show all your working in binary.
Answer = 0100 1110;
Carry row = 0010 0011;
The 1 carry bits (or some similar notation) must be shown in the correct columns (or correct sequence) but 0 carry bits can be omitted.
Show how the 8-bit two’s complement binary integer 00011100 can be subtracted from the 8-bit two’s complement binary integer 00111011 without converting the numbers to decimal.
You must show all your working in binary.
1 mark for correct conversion from 00011100 (28) to 11100100 (-28)
1 mark for binary addition of 00111011 (59) to 11100100 (-28) to give 00011111
//
2 marks for a correct final answer provided relevant working is shown and the working uses two’s complement in an attempt to solve the problem
A. If no other marks awarded, award 1 mark for correct conversion of 00111011 (59) to 11000101 (-59)
R. Reject both marks if decimal subtraction has been used
The bit pattern in Figure 1 represents a 10-bit unsigned fixed point binary number with four bits before and six bits after the binary point.
Figure 1
0 1 1 1 0 1 0 1 1 0
Convert the bit pattern in Figure 1 to decimal.
7.34375 // 7 11/32 // 235/32;
1 mark for correct integer part (or a numerator that produces the correct integer part when an improper fraction shown)
1 mark for correct fractional part
State the name of the component on a sound card that transforms the continuous signal received from a microphone to a form that can be stored by a computer.
Analogue to Digital Converter // ADC;
A bitmap image is 52 pixels in height and 26 pixels in width. The bitmap representation of the image requires 845 bytes.
Calculate the maximum number of colours that could be used in the bitmap image.
You should show all your working.
25 // 32
1 mark awarded for working out the colour depth (5) used in the bitmap image if the correct answer is not shown
(845 × 8)
(52 × 26)
When a bitmap image is stored in a file, additional information is stored as well as the colours of the pixels. For example, the bitmap file might contain information on the date of creation, image width and height.
State the name given to this additional information when storing a bitmap image.
Metadata;
A sound is recorded with a sample rate of 96 000 Hz and a sample resolution of 24 bits. The file size of the recording is 12 096 kilobytes.
A sample rate of 1 Hz means that one sample has been taken every second.
Calculate the duration of the sound recording.
You should show all your working.
3 marks for the correct answer including the unit of time 42 seconds
or 2 marks for 42 with no time unit
If answer is incorrect then award 1 method mark for two or three steps from the list below or 2 method marks for all four steps.
- multiplying by 8000
- multiplying by 12 096
- dividing by 24 // multiplying by 24 on same side of = as the time value
- dividing by 96 000 // multiplying by 96 000 on same side of = as the time value
The following method points are equivalent to performing two of the method points in the list above:
- multiplying by (or showing a numerator of) 96 768 000
- dividing by (or showing a denominator of) 2 304 000 // multiplying by 2 304 000 on same side of the = as the time value
A sample resolution of 16 bits is commonly used in audio recordings.
Explain why increasing the sample resolution from 16 bits to 24 bits can improve the quality of an audio recording.
There is reduced quantisation error // each sample can be represented/stored more accurately;
NE. improved sound quality
NE. increases accuracy of measurement
R. references to more samples / sample rate
MIDI does not use sampling to represent music.
Describe how music is represented using MIDI.
Music represented as sequence of MIDI (event) messages // uses messages to represent different events in a piece of music;
A. Music represented as sequence of instructions
NE. Music represented as sequence of notes
Playback of music is the combination of event messages with a specified ordering;
One example of data that might be contained in a message:
- Channel
- Note on / note off
- Pitch / frequency / note number
- Volume / loudness
- Velocity
- Key pressure / aftertouch
- Duration / length
- Timbre
- Instrument
- Pedal effects
- Pitch bend
- Note envelope;
MIDI messages are usually two or three bytes long;
First byte of each MIDI message is a status byte (others are data bytes);
Bit rate is 31 250 bits per second;
MSB value of 1 indicates status byte, 0 indicates data bytes;
Status bytes are divided into a command and a channel number (4 bits for each);
Sixteen channels are supported;
Explain one advantage of using MIDI instead of sampled sound to represent music.
- File sizes are (typically) smaller // More compact representation;
- Easy to modify/edit (at note level);
- Ease of manipulation for entire recordings // easy to change recording values (eg changing an octave for an entire score);
- Easy to change instruments;
- Simple method to compose algorithmically;
- Musical score can be generated directly from a MIDI file;
- A MIDI file can be directly output to control a device;
- MIDI records the musician’s inputs rather than the sound produced;
- Ease of composing/combining/overlaying existing recordings;
- No data lost about musical notes // no data lost through sampling;
- A. “better quality” but only if it there is some explanation of this eg “no error introduced during sampling”, “no background noise recorded”
A message is encrypted using a Caesar cipher that operates with a shift value of four. For example, the letter A in plaintext would be represented by E in ciphertext.
The ciphertext for the message is WSSDI.
What is the plaintext for the message?
SOOZE;
Explain two reasons why Caesar ciphers are vulnerable to being cracked.
Each letter/character is always encrypted to the same letter/character;
The letters/characters in the ciphertext will have the same frequency as their corresponding letters/characters in the plaintext (allowing the correspondence to be worked out given enough ciphertext);
A. The ciphertext is susceptible to frequency analysis
There are a very small number of possible keys (25 A.26) (so it can be cracked by brute force);
If a single mapping is known then the remaining (25) can be easily calculated;
The ciphertext will retain structural properties of the plaintext message;
A. Examples of structural properties, eg some letters frequently occur next to each other, some letters rarely appear next to each other, position of spaces can identify word lengths, common short words can be identified
Shade one lozenge to indicate which of the following is an example of system software.
- A Computer game
- B Image editor
- C Programming language translator
- D Video conferencing software
- E Word processor
C (Programming language translator);
An operating system manages hardware resources, for example the I/O devices associated with a computer system.
State two other examples of hardware resources that an operating system is responsible for managing.
- Processor // microprocessor // central processing unit // CPU;
- Main memory // random access memory // RAM;
A. Memory controller - Secondary storage // backing store;
A. HDD // SSD - Cache;
A. Cache controller - Power supply unit // battery management // PSU;
- R. Software-implemented resources (eg scheduler, virtual memory, file management)
Figure 2 shows the symbol for a logic gate.
State the name of the logic gate shown in Figure 2.
XOR // EXOR // EX-OR // Exclusive-OR // EOR;
Figure 3 shows a logic circuit.
Complete the truth table for the logic circuit in Figure 3.
| A | B | C | L | M | Z |
|---|---|---|---|---|---|
| 0 | 0 | 0 | |||
| 0 | 0 | 1 | |||
| 0 | 1 | 0 | |||
| 0 | 1 | 1 | |||
| 1 | 0 | 0 | |||
| 1 | 0 | 1 | |||
| 1 | 1 | 0 | |||
| 1 | 1 | 1 |
1 mark for columns L and M correct
1 mark for column Z correct
A. follow through of incorrect values in columns L and M
| A | B | C | L | M | Z |
|---|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 1 | 0 | 0 | 0 |
| 0 | 1 | 0 | 0 | 0 | 0 |
| 0 | 1 | 1 | 0 | 0 | 0 |
| 1 | 0 | 0 | 0 | 0 | 0 |
| 1 | 0 | 1 | 0 | 1 | 1 |
| 1 | 1 | 0 | 1 | 0 | 1 |
| 1 | 1 | 1 | 1 | 1 | 1 |
R. Entire column if more than one value shown in any cell of that column.
Figure 4 shows a logic circuit.
Write a Boolean expression for Q.
Award full marks for showing correct expression:
Q = (A'.B.(C + D))'
Max 2 marks for showing partially correct expression:
- 1 mark for showing A. B
- 1 mark for showing of C + D
- 1 mark for using AND and NOT gates to combine and invert subexpressions
Full marks should be awarded for equivalent expressions.
Using the rules of Boolean algebra, simplify the following expression.
W ⋅ X ⋅ Z + W ⋅ Z + X ⋅ Y ⋅ Z + W ⋅ X ⋅ Y ⋅ 1
You must show your working.
Final answer
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).
Award up to 3 marks for working. 1 mark per application of a technique that produces a simplified expression. Of the 3 working marks award at most 1 mark for correctly applying the Distributive Law to expand or introduce brackets.
Note: A simpler expression is one that is logically equivalent to the original expression but uses fewer logical operators.
1 mark for final answer: X ⋅ Z + X ⋅ Y + W ⋅ Z or X ⋅ (Z + Y) + W ⋅ Z
Example working 1:
W ⋅ X ⋅ Z + W ⋅ Z + X ⋅ Y ⋅ Z + W ⋅ X ⋅ Y ⋅ 1
W ⋅ X ⋅ Z + W ⋅ Z + X ⋅ Y ⋅ Z + W ⋅ X ⋅ Y Identity A.1 = A
Z ⋅ (W ⋅ X + W) + X ⋅ Y ⋅ Z + W ⋅ X ⋅ Y Distributive, put into brackets
Z ⋅ (X + W) + X ⋅ Y ⋅ Z + W ⋅ X ⋅ Y A̅.B + A = B + A
X ⋅ Z + W ⋅ Z + X ⋅ Y ⋅ Z + W ⋅ X ⋅ Y Distributive, expand brackets
X ⋅ (Z + Y ⋅ Z) + W ⋅ Z + W ⋅ X ⋅ Y Distributive, put into brackets
X ⋅ (Z + Y) + W ⋅ Z + W ⋅ X ⋅ Y A̅.B + A = B + A
X ⋅ Z + X ⋅ Y + W ⋅ Z + W ⋅ X ⋅ Y Distributive, expand brackets
X ⋅ Z + X ⋅ Y ⋅ (1 + W) + W ⋅ Z Distributive
X ⋅ Z + X ⋅ Y + W ⋅ Z Identity 1 + A = A
X ⋅ (Z + Y) + W ⋅ Z (optional step)
Example working 2:
W̅.X.Z+W.Z+X.Y.Z̅+W̅.X.Y
W̅.X.Z+W.Z+X.Y.Z̅+W̅.X.Y Identity A.1 = A
Z.(W̅.X+W) + X.Y.Z̅+W̅.X.Y Distributive, put into brackets
Z.( X+W) + X.Y.Z̅+W̅.X.Y Identity A̅.B + A = B + A
Z.X + Z.W + X.Y.Z̅+W̅.X.Y Distribution, expand brackets
Z.W + Z.X + X.Y.Z̅+W̅.X.Y Re-arrange terms
Z.W+ X(Z+Z̅.Y) + W̅.X.Y Distribution, put into brackets
Z.W+ X(Y + Z) + W̅.X.Y Identity A̅.B + A = B + A
Z.W + X.Y + X.Z + W̅.X.Y Distribution, expand brackets
X.Z + Z.W + X.Y + W̅.X.Y Re-arrange terms
X.Z + Z.W + X.Y Identity A + A.B = A
Figure 5 shows some of the processor registers and buses that are used during the fetch stage of the fetch-execute cycle, together with the main memory.
State the name of the components that are labelled in Figure 5 with the numbers 1 to 4. In the case of register names, the full names must be stated.
- 1 mark for two or three components correctly identified
- 2 marks for four components correctly identified
- Memory Address Register
- Address Bus
- Memory Buffer Register A. Memory Data Register
- Data Bus
Describe the stored program concept.
(Machine code) Instructions are stored in (main) memory;
Instructions are fetched, (decoded) and executed (serially) by the processor;
Programs can be moved in to (and out of) main memory;
In a particular processor instruction set, each instruction consists of an opcode and an operand. An operand could be an immediate value to be used by a program.
State two other types of value that can be stored in an operand.
- Register (number);
- Memory address / location;
- A. offset from a memory location
Computer A and Computer B both have a processor with a clock speed of 2.8 GHz but Computer A performs tasks much faster than Computer B. Computer A has a larger cache and greater word length than Computer B.
Explain why the larger cache and greater word length are possible factors for the performance difference between Computer A and Computer B.
Increases the probability/likelihood/chance that data/instructions will be found in cache (and cache memory is faster than main memory);
A. Increases probability/likelihood/chance of cache hit (without cache hit definition)
A. Fewer accesses to slower memory types, eg main memory
A. More instructions can be accessed from high speed memory
Allows for more bits to be simultaneously processed (in the execution of a single instruction) // Allows for more bits to be simultaneously transferred (within the processor);
Registers R1 and R3 each store a different positive number.
Write a program using the standard AQA assembly language that will:
- store the greater of these two numbers in R1
- store 1 in R2 if the value originally in R1 is greater than the value in R3, storing 3 in R2 otherwise.
- Comparing the values in R1 and R3
A. Indirect comparisons - Using a branch instruction to execute different blocks of code.
- Always terminating with the greater number stored in R1.
- Terminating with 1 stored in R2 when the greater number was in R1 and 3 stored in R2 otherwise.
Max 3 marks for programming if any syntax incorrect or program does not work correctly under all circumstances
Example 1
CMP R1, R3
BGT r1bigger
MOV R1, R3
MOV R2, #3
B Done
r1bigger: MOV R2, #1
done: HALT
Example 2
SUB R2, R1, R3
CMP R2, #0
BGT finish
MOV R2, #1
B done
finish: MOV R1, R3
MOV R2, #3
done: HALT
Example 3
MOV R2, #1
CMP R1, R3
BGT done
MOV R1, R3
MOV R2, #3
done: HALT
RFID tags can be read by an RFID reader.
Describe how data is read from an RFID tag.
The RFID reader emits radio waves;
(The antenna in the RFID tag allows) the radio waves to induce sufficient power in the tag to enable/power the tag // triggers an active tag;
Data is stored on the chip/memory of the tag;
In response the tag emits radio waves to transmit the data on the tag to the RFID reader;
A. Frequency or signal for radio waves
Note: Accept references to data, instead of radio waves, if it is made clear somewhere in the response that radio waves/signals/frequencies are being used.
An RFID tag can be active or passive. A passive tag must be moved within a few centimetres of an RFID reader to be read. An active tag will have its own power source, which allows it to be read from a greater distance.
It is decided that RFID tags will be used in passports to store personal information.
Explain why passive tags are likely to be a more appropriate choice than active tags for use in passports.
- Passive tags are smaller // are more convenient for users to carry;
- (As passive tags can only be read when close to the reader) it is less of a security risk // it is more difficult to intercept/steal the data from the passport;
- Using passive tags is likely to be cheaper than using active tags (especially at a national scale);
- In passive tags there is no need to replace/charge battery // in active tags battery may not last as long as the passport is valid;
Accept points made as disadvantages of active tags or as advantages of passive tags
A smartphone company has designed a device that can be put into items such as luggage to help locate these items if they are lost. The device works by sending an encrypted signal containing its current location to nearby smartphones. The smartphones relay the signal to the company’s servers via the Internet, allowing a user to see the device’s exact location using a mobile phone app.
The company expects to sell hundreds of millions of devices. The data collected from each device will be permanently kept in secondary storage on the company’s servers. The company is planning to use solid-state drives in the servers that will hold device location data but is unsure whether using solid-state drives is a good idea.
Discuss a range of moral, ethical, legal and cultural issues raised by the new device and explain the properties of solid-state drives that the company should consider when deciding on a secondary storage technology.
In your answer you will be assessed on your ability to follow a line of reasoning to produce a coherent, relevant and structured response.
Level 3
A line of reasoning has been followed to produce a coherent, relevant, substantiated and logically structured response. Answers in this level will demonstrate a clear and detailed awareness of the properties of solid-state drives. The response covers a wide range of issues and is likely to cover the moral ethical, legal and cultural aspects of the question. Several of the points made will have been expanded upon using clear examples and references to real-world implications.
Level 2
A line of reasoning has been followed to produce a mostly coherent, relevant, substantiated and logically structured response. Answers in this level will identify a small number of properties of solid-state drives but may fail to develop points. The response is likely to cover at least two of moral, ethical, legal and cultural aspects of the question. Some of the points made may have been expanded on.
Level 1
There is little evidence that a line of reasoning has been followed. Answers in this level may identify some properties of solid-state drives. Answers may have attempted to identify some moral, ethical, legal and cultural issues. Points are not likely to be expanded upon but where they are, the examples may not be relevant or not relate to the points being made.
Indicative content
Area 1: Moral, ethical, legal and cultural issues
Moral (individual beliefs)
There is the potential for the technology to be misused by criminals (eg stalking, tracking partners/children/pets/strangers/property without permission).
Criminals could put them into the pockets/luggage of targets/victims/children to find out where they live.
Individuals might become over-reliant on the technology and not look after their property.
Individuals might not wish for their phones to be used to send signals on behalf of other users or in support of the company’s network, even with encryption.
Ethical (society)
Right to privacy eroded as your movements are tracked by the company.
“Big Brother” society where your every move is monitored and analysed.
Could it be used to track people in a good way, for example elderly or ill patients.
Individuals in some jurisdictions will have had to agree for their phones to relay signals in support of the company’s network but they may not want to or even know that they have agreed to such terms.
Legal
As the tag moves internationally through different countries different laws will exist about data collection and privacy.
Computer Misuse Act would be applied in the UK to prevent unauthorised access to the tag and the location data.
General Data Protection Regulation (GDPR) affords protections to data subjects and provides rights relating to access, accuracy, deletion, etc.
Cultural (subgroups)
Older people might be very distrustful or fearful of this technology.
This tag would only work in an area with a high number of phones / phone coverage, therefore it is not suitable for rural locations or places with few phone users for other reasons.
Different societies may have different views on the privacy issues related to location tracking.
Area 2: Suitability of storage device
Solid-state drive properties:
Higher read and write speeds than hard disks (because there are no moving parts means they’d be more likely to keep up with the requests).
Less prone to (terminal) failure from dropping/collisions/movement (because there are no moving parts or joints), which means there is less likelihood of costs being incurred from damaged drives.
Generally more energy efficient, which can lead to reduced costs (operational and/or cooling), provide a cooler / more comfortable operating environment, and be more environmentally friendly.
Generally small in physical size, which means that the amount of space required to house them / operational cost can be reduced.
More expensive (per bit) for the same amount of memory, (which means that the company would be investing more in the purchase of the drives initially).
The lifetime of a solid-state drive is relatively fixed, due to there being an approximate maximum number of writes before it becomes unreliable/unusable.
Describe the difference between baud rate and bit rate.
Bit rate is the number of bits transmitted per second;
Baud rate is the number of times that a signal can change per second (on a medium);
A photographer wants to create a large file sharing network to allow thousands of photographers to share their photos with each other for free.
State two reasons why the photographer may choose to use a peer-to-peer network rather than a client-server network.
- Each user has equal status // each user can use and provide file sharing services // users can individually control who can access their photographs // users manage their own security;
- Easier / less expensive to setup/maintain (than a centralised server);
- Provides scalability without the need for a high-performance server/hardware;
- No reliance on central server // (some of the) service remains available if one peer fails;
Explain the purpose of a Service Set Identifier (SSID).
(A locally unique) identifier (A. name) given to a wireless network // (SSID) allows a user/device to identify/connect to (A. join) network);
NE. To find the network without reference to identifier or connection.
Explain how disabling SSID 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;
Only users who know the SSID of the network can connect // users who do not know the SSID cannot connect // makes it harder for a (malicious) user to connect unless they know the SSID;
A. name for SSID
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). |