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 values represented by the letters A–D in Table 1 is a natural number.
- A:√2
- B:(−9)2
- C:−4
- D:0.5
B;
R. More than one lozenge shaded
Shade in one lozenge to indicate which of the values represented by the letters A–D in Table 1 is an irrational number.
- A:√2
- B:(−9)2
- C:−4
- D:0.5
A;
R. More than one lozenge shaded
Shade in one lozenge to indicate which of the values represented by the letters A–D in Table 1 is an integer but not a natural number.
- A:√2
- B:(−9)2
- C:−4
- D:0.5
C;
R. More than one lozenge shaded
Figure 1 contains a bit pattern.
Figure 1
00111001
What is the hexadecimal equivalent of the bit pattern shown in Figure 1?
39;
A. #39
Why do programmers often use hexadecimal instead of binary to represent bit patterns?
More compact when displayed;
Easier (for people) to understand/remember; A. read
Lower likelihood of an error when typing in data;
Saves (the programmer) time writing/typing in data;
NE takes up less space
R. if answer states that hexadecimal uses less memory/storage
Max 1
What is the decimal equivalent of the bit pattern shown in Figure 1 if it represents an unsigned fixed-point binary value with four bits before the binary point and four bits after the binary point?
3 9/16
//
3.5625
Mark as follows:
1 mark for correct integer part (3)
1 mark for correct fractional part (9/16 or .5625)
Alternative answer
57/16;;
What is the decimal equivalent of the bit pattern shown in Figure 1 if it represents a two’s complement binary integer?
57;
The ASCII code for the numeric character "0" is 4810; other numeric characters follow on from this in sequence.
What character is represented by the bit pattern in Figure 1 if it is an ASCII code?
9;
I. Quotes around answer
I. subscript 10 after the answer 9
Parity bits are often used to detect errors during data transmission. If the most significant bit in the bit pattern in Figure 1 (the leftmost bit) is a parity bit, explain how the value of this was calculated by the sending device before the byte was transmitted. You should assume that the even parity system is being used.
The number of 1s (in the other 7 bits) has been counted // there are four 1s (in the 7 bits);
there are an even number of 1s so the parity bit has been set to 0 (to keep the number of 1s even);
Alternative answer
The 7 data bits have been XORed;
The result is a 0 so the parity bit has been set to 0 (so the result of XORing the 8 bits will be 0);
Majority voting is an alternative to using parity bits. Explain how the majority voting system works in the context of data transmission.
AO1 knowledge – 1 mark:
Each bit is sent multiple times; A. A specified (odd) number greater than 2, instead of multiple
Marking guidance – to get this mark sent/sender must be clear
AO1 understanding – 1 mark:
The receiver checks the bits it has received and if they are not all the same it assumes the one it received the most copies of is the correct value for the bit; R. receiver knows that the bit is correct A. receiver takes as correct (or similar)
Marking guidance – to get this mark received/receiver must be clear
A. alternative answer using majority voting with a whole byte instead of individual bits
AO1 knowledge – 1 mark:
The bit pattern (R. data) is sent multiple times; A. A specified number greater than 2, instead of multiple
Marking guidance – to get this mark sent/sender must be clear
AO1 understanding – 1 mark:
The receiver checks the bit patterns (R. data) it has received and if they are not all the same it assumes the one it received the most copies of is the bit pattern (R. data) that was sent; R. receiver knows that the bit pattern is correct A. receiver takes as correct (or similar)
Marking guidance – to get this mark received/receiver must be clear
Using the rules of Boolean algebra, simplify the following Boolean expression.
(A' + B).(A + (B + A)')'
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:
Max 3 for working; Max 3 if answer is correct but any incorrect working or significant steps of working is missing:
1 mark for a successful application of De Morgan's Law that would lead to a simpler expression. Max 2 for applications of De Morgan's Law.
1 mark for applying an identity other than cancelling nots that produces a simpler expression. Max 2 for applying identities.
1 mark for expanding brackets or putting an expression into brackets that would lead to a simpler expression. Max 2 for expanding brackets or putting an expression into brackets.
Note: a simpler expression is one that is logically equivalent to the original expression but uses fewer logical operators.
Example working (1)
( )
)
) [application of De Morgan's law]
( )
) [expansion of brackets]
( )
) [use of identities = 0 and X+0 = X]
[expansion of brackets]
BABA ..
[use of identity
XXX .
twice]
[use of identity
XXX
]
Alternative example working (2)
))(()( ABABA
[application of De Morgan's Law]
).(. ABABA
[application of De Morgan's Law twice]
)..(. AABABA
[expansion of brackets]
BABA ..
[use of identities
0. AA
and
XX 0
]
BABA .
[application of De Morgan's Law]
).).(( BABA
[application of De Morgan's Law]
BABBAA ....
[expansion of brackets]
BABA ..
[use of identity
XXX .
twice]
[use of identity
XXX
]
Alternative example working (3)
[application of De Morgan's Law]
[De Morgan's Law twice]
[Expansion]
[Identity
0. AA
and
AA 0
]
[application of De Morgan's Law]
[application of De Morgan's Law]
BABBAA ....
[Expansion]
[Identity and
BBB .
]
[Final answer via identity
AAA
]
))(()( ABABA
).(. ABABA
)..(. AABABA
BABA ..
BABA .
).).(( BABA
BABA .. AAA .
BA.
BA.
Assembly language is considered to be a low-level language. Which other type of language is also considered to be a low-level language?
Machine code;
A. bytecode
A. object code
I. reference to binary
A. machine (language) as BOD
All even numbers are represented by bit patterns ending with a 0; all odd numbers are represented by bit patterns ending with a 1.
Complete the assembly language instruction below to help identify if register R1 contains an odd number, storing the result of this operation in register R3.
AND R3, R1, _____
#1;
R. 1
I. zeroes between # and 1
Refer answers that start with #1 and then have any other writing to senior examiner
Figure 4 shows a block of code, written in a high-level language, that is used to find out if the number stored in the variable A is even. If the value is even then the number 69 is stored in the variable B, otherwise the number 79 is stored in the variable B.
Figure 4
IF IsEven(A)
THEN B ← 69
ELSE B ← 79
ENDIF
Write a sequence of assembly language instructions that would perform the same operations as the high-level language code in Figure 4.
Assume that register R1 currently stores the value associated with A, that register R2 stores the value currently associated with B and that register R3 is available for general use, if necessary.
Your answer to question 04.2 can be reused as part of your answer to this question.
AO3 (design) – 2 marks:
1 mark: Identifying that a comparison and branch are required to have the same effect as the IF statement, even if the syntax or comparison made are incorrect
1 mark: Identifying that one or more labels are needed for branching to work
AO3 (programming) – 4 marks:
For the AO3 (programming) marks, the syntax used must be correct for the language as described on the question paper.
1 mark: Comparing R3 against 1 or 0 and having a branch with the correct logical condition
1 mark: For moving 69 to R2 in the equivalent of the THEN part A. moving 69 to R2 in equivalent of ELSE part if this is appropriate for compare and branch statements used
1 mark: For having an unconditional branch that results in skipping over 2nd move instruction or HALT in appropriate place
1 mark: For moving 79 to R2 in the equivalent of the ELSE part A. moving 79 to R2 in equivalent of THEN part if this is appropriate for compare and branch statements used
Max 3 marks for programming if any syntax incorrect or program does not work correctly under all circumstances
I. Missing AND instruction at start of answer.
I. Incorrect AND instruction at start of answer.
I. Load instruction to setup R1 from A.
I. Store instruction to store R2 into B.
A. Labels given in any sensible format
A. Answers that use hexadecimal or binary values
A. Line numbers as equivalent to labels if they are used as the target of branches. Note: in future this will not be accepted as line numbers are not part of the AQA assembly language.
DPT Missing hash for immediate addressing
DPT incorrect use of commas, colons, semi-colons, etc…
Refer alternative answers to team leaders
Example solutions:
AND R3, R1, #1
CMP R3, #1
BEQ odd
MOV R2, #69
B end
odd:
MOV R2, #79
end:
//
AND R3, R1, #1
CMP R3, #1
BEQ odd
MOV R2, #69
HALT
odd:
MOV R2, #79
//
AND R3, R1, #1
CMP R3, #1
BNE even A. BLT instead of BNE
MOV R2, #79
B end
even:
MOV R2, #69
end:
//
AND R3, R1, #1
CMP R3, #0
BNE odd A. BGT instead of BNE
MOV R2, #69
B end
odd:
MOV R2, #79
end:
//
AND R3, R1, #1
CMP R3, #0
BEQ even
MOV R2, #79
B end
even:
MOV R2, #69
end:
Shade in one lozenge to indicate which addressing mode is being used with the second operand in the assembly language instruction MOV R2, #0.
- A:Direct
- B:Immediate
Immediate;
R. More than one lozenge shaded
Explain what a register is.
A memory/storage location inside the processor; A. CPU instead of processor
NE memory/storage location
What is the name of the logic gate represented by the truth table and symbol shown in Figure 5?
Figure 5
| X | Y | Z |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
XOR // EOR // Exclusive OR;
The value at M (indicated by the arrow in Figure 6) is represented by the following Boolean expression:
1 . C'
Simplify this Boolean expression.
C';
The output T (in Figure 6) is represented by the following Boolean expression:
1 ⊕ C'
Simplify this Boolean expression.
C;
Complete the missing cells in Table 3.
Table 3 – Four rows of the truth table for the circuit in Figure 6
| Inputs | Outputs | |||||
|---|---|---|---|---|---|---|
| C | B | A | T | S | R | |
| 0 | 0 | 0 | 0 | 0 | 0 | |
| 0 | 0 | 1 | ||||
| 0 | 1 | 0 | ||||
| 0 | 1 | 1 | 0 | 1 | 0 | |
| C | B | A | T | S | R |
|---|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 1 | 0 | 0 | 1 |
| 0 | 1 | 0 | 0 | 1 | 1 |
| 0 | 1 | 1 | 0 | 1 | 0 |
Mark as follows:
1 mark: column T correct;
1 mark: column S correct;
1 mark: column R correct;
The logic circuit shown in Figure 6 obtains the two’s complement of a 3-bit binary number. Explain how this circuit could be used by a processor when subtracting one 3-bit binary number from another.
Use this circuit on the binary number to be subtracted and add the result to the other binary number;
A. Any equivalent answers
R. Number to be added IS negative
The circuit in Figure 6 can be simplified so that it uses fewer logic gates but still has the same functionality. Changing the design of the circuits used in a processor can improve processor performance. Increasing the number of cores can also improve processor performance.
State three other factors that can improve processor performance. For each factor, explain how it will improve processor performance.
1 mark for AO1 (knowledge): (increase the) data bus width;
1 mark for AO1 (understanding): enables more bits (A. data) to be transferred between main memory and the processor at one time (so fewer read/write operations needed);
1 mark for AO1 (knowledge): (increase the) clock speed;
1 mark for AO1 (understanding): enables more instructions to be executed per unit of time/second (A. calculations/operations/commands instead of instructions) // each individual instruction could be executed sooner / more quickly (A. calculation/operation/command instead of instruction);
1 mark for AO1 (knowledge): (increase the) amount of cache memory;
1 mark for AO1 (understanding): cache memory is faster than main memory so the more that can be stored in cache memory the less frequently the main memory needs to be accessed;
1 mark for AO1 (knowledge): (increase the) word length;
1 mark for AO1 (understanding): larger word size means that the processor can process more bits in one go;
1 mark for AO1 (knowledge): (change the) type of cache memory;
1 mark for AO1 (understanding): some types of cache memory can be accessed faster;
A. using memory with a faster access speed
1 mark for AO1 (knowledge): (increase the) number of general purpose registers;
1 mark for AO1 (understanding): more intermediate results/variables can be kept in processor registers rather than in main memory;
1 mark for AO1 (knowledge): (increase the) address bus width;
1 mark for AO1 (understanding): enables the processor to access a larger number of main memory locations (meaning it will not need to make as much use of virtual memory this will mean that system performance is improved); A. allows more main memory to be installed
R. How improves mark if it is not relevant for the factor stated.
NE How improves of "program will execute faster"
Note: marks for the factor can be awarded in either the "factor" or "how improves" part of an answer
What is the minimum file size in bytes of the image shown in Figure 7 when it is represented using a bitmap?
You may get some marks for your working even if your answer is incorrect.
16 * 16 * 2 / 8 = 64
Mark as follows:
1 mark: working out that there are 256 (16*16) pixels in the image
1 mark: multiplying by 2
1 mark: dividing by 8 so that number of bits needed is converted to number of bytes needed
Max 2 if final answer is not correct.
Award all 3 marks if final answer is correct.
Explain why the actual file size for the image will be larger than the minimum file size calculated for your answer for 06.1.
Because metadata will also be stored // other data about the image will be stored;
A. by example eg width in pixels / height in pixels / (colour) depth of image will also be stored
If the number of colours used in the image in Figure 7 were increased by two, what is the minimum number of extra bits that would be needed to represent each pixel?
1;
Image files are often compressed so that they take up less storage space. Describe how run length encoding (RLE) could be used to compress the image shown in Figure 7.
Store the colour of a pixel and a count; A. by example
the count indicates the number of pixels of that colour there are before a pixel of a different colour is used in the image // the count indicates the total number of pixels of that colour there are in a run // the count indicates the number of consecutive pixels of the same colour;
What hardware component is needed for each device that is going to be connected to the wireless network?
Mark as follows:
One of: wireless/network/wireless network
Followed by one of: adapter/dongle/card/interface card;
A. NIC
A student is trying to use his own mobile device on the school network. He has all the necessary hardware and software, all the hardware devices are working correctly and he knows the correct SSID and WPA2 key for the school network. However, he is still not able to connect to the wireless network.
Describe a security measure, other than logging in, that the school might have put in place that is preventing this student from connecting his own mobile device to the network.
MAC address white list/filtering; A. description of a whitelist
Wireless access points check MAC address of device trying to connect to network against list of allowed addresses;
Only devices with an allowed MAC address are able to connect // devices without an allowed MAC address are not able to connect;
DPT wrong type of address, eg IP address, or no type of address specified
Note for examiners: refer other plausible methods to team leader
Explain why preventing students from using their own mobile devices on the wireless network is likely to improve the performance of the school network.
A network has limited bandwidth;
(Preventing some devices from using the network will mean that) more bandwidth available for other devices/users // (preventing some devices from using the network) will decrease network traffic;
(Fewer devices on the network means) reduced likelihood of two devices transmitting simultaneously or transmissions interfering with each other/colliding;
Max 2
Explain the role of a Service Set Identifier (SSID) in wireless networking.
AO1 (knowledge):
1 mark: SSID is a (locally unique) identifier for a wireless network;
AO1 (understanding):
1 mark: A wireless client must use the same SSID as the one put in the access point to join // which prevents clients from accessing the wireless network unless they are using the same SSID as the access point;
WPA2 is an example of a protocol. Explain what is meant by the term protocol.
Set of rules; that allow two devices to communicate;
Three input devices that could be used at each checkpoint to capture data automatically as competitors pass by are:
- barcode reader
- digital camera
- RFID reader
The race organisers decide to use RFID readers. Evaluate the suitability of all three devices and explain why RFID is the most appropriate choice.
| Level | Description | Mark Range |
|---|---|---|
| 3 | A detailed summary of the suitability / non-suitability has been given, indicating a comprehensive understanding of all three devices/technologies. The answer is well structured and a line of reasoning has been followed to produce a coherent, relevant, substantiated and logically structured response. A well-reasoned conclusion has been included featuring at least two reasons for RFID being most suitable for 5 marks and three reasons for RFID being most suitable for 6 marks. | 5-6 |
| 2 | Appropriate reasons, linked to the scenario in the question, have been given for the suitability / non-suitability of all three devices/technologies – though there may not be a reasoned conclusion and the reason(s) for RFID readers being suitable may be brief. The answer is satisfactorily structured. | 3-4 |
| 1 | A small number of reasons for the suitability / non-suitability of one or more of the devices have been given indicating some understanding of the input devices. However, there is no comparison and the understanding shown is not well-linked to the scenario described in the question. | 1-2 |
| 0 | No creditworthy material | 0 |
Indicative subject content
Digital camera
• Advantage: no tag/code that can be lost / damaged
• Disadvantage: difficulties with taking a clear picture eg caused by blocked line of sight due to other competitors
• Disadvantage: high data storage requirements for the number of photos that will be needed in a large event
• Disadvantage: face recognition may not work eg due to costumed runners
• Disadvantage: face recognition software not always reliable
• Disadvantage: with a lot of competitors a lot of operators/cameras might be needed
Barcode reader
• Advantage: barcodes are very cheap
• Advantage: often smaller and lighter than an RFID tag so less of a burden to competitors
• Disadvantage: barcode could be obscured (e.g. by clothing)
• Disadvantage: difficult to scan a code that is being moved around and is not on a flat surface
• Disadvantage: some codes might be missed if a large number of competitors pass a checkpoint at roughly the same time
• Disadvantage: with a lot of competitors a lot of operators/barcode readers might be needed
• Disadvantage: scanner needs to be quite close to code / runners may need to stop to have their barcode scanned
• Disadvantage: barcode more likely to be damaged than RFID tag – when it is damaged it is unreadable
RFID reader
• Advantage: RFID can be read faster than the other devices and competitors may be going past the checkpoint quickly
• Advantage: tags potentially reusable – saving money in future years of the event
• Advantage: no line-of-sight issues
• Advantage: no need for runner to stop at checkpoint
• Disadvantage: potential for RFID dead spots
Note: advantage/disadvantage for device must be an advantage/disadvantage compared to (at least) one of the other devices listed in the question for mark to be awarded.
State two reasons why the computer has a magnetic hard disk and a solid-state drive instead of using only solid-state storage.
Because hard disk drives are cheaper (per unit of storage) than solid state drives // because SSDs are more expensive (per unit of storage) than hard disks;
Because hard disk drives have a higher capacity than solid state drives // because SSDs have a lower capacity than hard disk drives;
State two hardware components of a solid-state drive.
NAND (flash) memory; A. NOR (flash) memory A. Floating gate transistor A. flash memory NE memory NE logic gates
Controller;
(SATA) interface;
Max 2
Some high-level languages are imperative. Explain the term imperative.
Instructions are executed in a programmer-defined order // Imperative high level language programs define sequences of commands for the computer to perform;
Imperative high level languages describe how to solve a problem (in terms of sequences of actions to be taken);
Explain the advantages and disadvantages of programming using imperative high-level languages compared with low-level languages.
Programs written in a high-level language are machine independent / portable;
People find it easier to debug high-level language programs;
People find it easier to read/write/understand high-level language program code;
High-level languages save time for programmers as they use fewer lines of program code;
Programs written in a high-level language may not make best use of specific features of a particular processor;
Programs written in a high-level language may not execute as quickly;
Some programs cannot be (easily) written using a high-level language – particularly some parts of a computer's operating system;
Programs written in a high-level language may use more memory;
Max 4
Max 3 if all advantages of one type of language or all disadvantages of one type of language
A program written in a high-level language needs to be translated using either a compiler or an interpreter before it can be executed. Describe two differences between a compiler and an interpreter.
A compiler produces object/machine code (A. executable file) whilst an interpreter does not // once code has been compiled it does not (normally) need to be recompiled whilst an interpreter has to translate code every time a program is run // if using an interpreter it needs the source code each time it executes the program whereas a compiler only needs to use the source code once;
A compiler translates the whole of the source code into object code (prior to execution) whilst an interpreter translates and executes line by line;
The object code produced by a compiler will execute faster once it is compiled than interpreting the source code (every time the program is run);
An interpreter can run (syntactically correct) parts of a program whilst there are syntax errors in other parts of it, which a compiler cannot;
Max 2
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). |