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A Level Computer Science 9618 Paper 33, May/June 2024

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9618/33 · May/June 2024

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1

Real numbers are stored in a computer system using floating-point representation with: • 10 bits for the mantissa • 6 bits for the exponent • two’s complement form for both the mantissa and the exponent.

a

Calculate the denary value of the given normalised floating-point number. Show your working. Mantissa 0 1 0 0 1 1 1 1 0 0 Exponent 0 0 1 0 0 1 Working ..................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... Answer ......................................................................................................................................

[3]
b

Calculate the normalised floating-point representation of –102.75 in this system. Show your working. Mantissa Exponent Working ..................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ...................................................................................................................................................

[3]
2

The TCP/IP protocol suite has four layers: Transport, Application, Link, Internet

a

Complete the diagram to show the correct order for these layers.

[2]
b

Describe the function of the Transport layer.

[2]
c

Outline one protocol that is associated with the Application layer.

[2]
3
a

Explain what is meant by non-composite and composite data types.

[3]
b

Write pseudocode statements to declare the record data type FootballClub to hold data about football clubs in a league, to include: • name of team • date team joined the league • main telephone number • name of the manager • number of members • current position in the league.

[4]
4
a

Describe the sequential method of file access.

[2]
b

Explain how the sequential method of file access is applied to files with serial organisation and to files with sequential organisation.

[3]
5
Figure 1 of 1 for question 5
a

Write this Reverse Polish Notation (RPN) in infix form: 5 2 + 9 3 - / 3 *

[3]
b

Write this infix expression in RPN: ((7 + 3) - (2 * 8)) / 6

[2]
c

Evaluate this RPN expression: a b - c d + * e / when a = 17, b = 5, c = 7, d = 3 and e = 10 Show the changing contents of the stack as the RPN expression is evaluated.

[4]
6

The diagram shows a logic circuit.

Figure 1 of 2 for question 6
Figure 2 of 2 for question 6
a

Complete the truth table for the given logic circuit. Show your working.

[3]
b

Write the Boolean expression that corresponds to the logic circuit as a sum-of-products. Z = ............................................................................................................................................

[2]
c(i)

Complete the Karnaugh map (K-map) for the Boolean expression: A‾.B‾.C‾+A‾.B‾.C+A.B‾.C‾+A.B‾.C+A.B.C‾+A.B.C

[2]
c(ii)

Draw loop(s) around appropriate group(s) in the K-map to produce an optimal sum-of-products.

[2]
c(iii)

Write the Boolean expression from your answer to part (c)(ii) as a simplified sum-of-products.

[1]
7
a

Describe what is meant by a digital certificate.

[3]
b

Explain the role of a digital certificate in creating a digital signature.

[2]
8

A declarative programming language is used to represent the features that are available and the features that are unavailable on different body styles of a car. 01 feature(sunroof). 02 feature(automatic_tailgate). 03 feature(heated_seats). 04 feature(extra_seats). 05 feature(reversing_camera). 06 feature(dashboard_camera). 07 feature(air_conditioning). 08 feature(heated_windscreen). 09 feature(satnav). 10 bodystyle(saloon). 11 bodystyle(hatchback). 12 bodystyle(estate). 13 bodystyle(minivan). 14 bodystyle(convertible). 15 available(sunroof, hatchback). 16 available(sunroof, minivan). 17 available(reversing_camera, hatchback). 18 available(extra_seats, minivan). 19 available(reversing_camera, saloon). 20 unavailable(sunroof, convertible). 21 unavailable(automatic_tailgate, saloon). 22 unavailable(extra_seats, hatchback). These clauses have the meanings: Clause Meaning 01 Sunroof is a feature. 10 Saloon is a body style. 15 Sunroof is available on a hatchback. 20 Sunroof is unavailable on a convertible.

a

Sliding doors is a feature that is available on a minivan but unavailable on a hatchback. Write additional clauses to represent this information. 23 ............................................................................................................................................. 24 ............................................................................................................................................. 25 .............................................................................................................................................

[3]
b

Using the variable Options, the goal: available(Options, saloon) returns Options = reversing_camera Write the result returned by the goal: available(Options, hatchback) Options = ........................................................................................................................

[1]
c

F may be available for B if F is a feature and B is a body style and F is not unavailable for that body style. Write this as a rule: may_choose_option(F, B) IF ............................................................................................................................................. ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................

[4]
9

Explain what is meant by Deep Learning in relation to Artificial Intelligence (AI).

[3]
10
a

State a condition that must be true for an array to be searchable for a binary search.

[1]
b

Complete the given pseudocode to find an item in a 1D array Names of type STRING using a binary search. DECLARE Names : ARRAY[1:100000] OF STRING DECLARE TopOfList : INTEGER DECLARE EndOfList : INTEGER DECLARE CurrentItem : INTEGER DECLARE ToFind : STRING DECLARE Found : BOOLEAN DECLARE NotInList : BOOLEAN TopOfList ← 1 EndOfList ← 100000 OUTPUT "Which name do you wish to find? " INPUT ToFind ................................................................................................................................................... NotInList ← FALSE WHILE ................................................ AND ................................................ CurrentItem ← (TopOfList + EndOfList) DIV 2 IF ........................................................................................................... THEN Found ← TRUE ELSE IF TopOfList >= EndOfList THEN ........................................................................................................... ELSE IF ToFind > Names[CurrentItem] THEN ........................................................................................................... ELSE EndOfList ← CurrentItem – 1 ENDIF ENDIF ENDIF ENDWHILE IF Found = TRUE THEN OUTPUT "Item found at position ", CurrentItem, " in array" ELSE OUTPUT "Item not in array" ENDIF

[5]
c

Describe the performance of a binary search in relation to the number of data items in the array being searched. Refer to Big O notation in your answer.

[2]
11

Reduced Instruction Set Computers (RISC) and Complex Instruction Set Computers (CISC) are two types of processor.

a

State two features of RISC processors.

[2]
b

Outline the process of interrupt handling as it could be applied to RISC or CISC processors.

[3]
c

Explain how pipelining affects interrupt handling for RISC processors.

[3]

Mark scheme

9618/33 · May/June 2024

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1a · 3 marks

  • 1 mark

    conversion of exponent 001001 to 9

  • 1 mark

    application of exponent to mantissa to go from 0.100111100 to 100111100 // 256 + 32 + 16 + 8 + 4 seen // 64/128 + 8/128 + 4/128 + 2/128 + 1/128 = 79/128 // 1/2 + 1/16 + 1/32 + 1/64 + 1/128 = 79/128

  • 1 mark

    correct answer = 316

1b · 3 marks

  • 1 mark

    number converted to binary 10011001.01 // number converted to positive 102.75, reversed bits and 1 added. (0)1100110.11  10011001.00  10011001.01 // -128 + 16 + 8 + 1 + 0.25 = –102.75

  • 1 mark

    exponent = 7 // Moving binary point the correct number of places

  • 1 mark

    correct answer (Mantissa: 1 0 0 1 1 0 0 1 0 1, Exponent: 0 0 0 1 1 1)

2a · 2 marks

  • 2 marks

    Application, Transport, Internet, Link in correct position

2b · 2 marks

  • 1 mark

    The transport layer is responsible for delivery of data from the source host to the destination host

  • 1 mark

    It is where data is broken up into packets and sent to the internet layer

2c · 2 marks

  • 1 mark

    Name of protocol

  • 1 mark

    Expansion of protocol

3a · 3 marks

  • 1 mark

    non-composite data types: Non-composite data types can both be user-defined or primitive / do not refer to other data types in their definition / contain one data type in their definition / can be primitive/enumerated/pointer

  • 1 mark

    composite data types: Composite data types can be user-defined or primitive / refer to other data types in their definition/contain more than one data type in their definition / can be record/set/class

  • 1 mark

    Additional valid point for non-composite or composite data types

3b · 4 marks

  • 1 mark

    TYPE FootballClub and ENDTYPE correct

  • 1 mark

    First two correct declarations

  • 1 mark

    Second two correct declarations

  • 1 mark

    Final two correct declarations

4a · 2 marks

  • 1 mark

    Sequential access method searches for records one after the other

  • 1 mark

    … from the physical start of the file until the record is found/the end of file.

4b · 3 marks

  • 1 mark

    For serial files, records are stored in chronological order

  • 1 mark

    … every record needs to be checked until the record is found, or all records have been checked.

  • 1 mark

    For sequential files, records are stored in order of a key field/index, and it is the key field/index that is compared.

5a · 3 marks

  • 1 mark

    (5 + 2)

  • 1 mark

    / (9 – 3)

  • 1 mark

    * 3

5b · 2 marks

  • 1 mark

    7 3 +

  • 1 mark

    2 8 * - 6 /

5c · 4 marks

  • 1 mark

    First ring

  • 1 mark

    Second ring

  • 1 mark

    Third ring

  • 1 mark

    Fourth ring

6a · 3 marks

  • 1 mark

    working, all four columns P, Q, R and S

  • 1 mark

    first four rows of column Z

  • 1 mark

    second four rows of column Z

6b · 2 marks

  • 2 marks

    all five correct terms and no extras: (Z =) Ā.B̄.C̄ + Ā.B̄.C + A.B̄.C + A.B.C̄ + A.B.C

6c(i) · 2 marks

  • 2 marks

    All values in Karnaugh map correct

6c(ii) · 2 marks

  • 1 mark

    Correct loop for row A=1 (group of 4)

  • 1 mark

    Correct loop for cells ĀB̄C̄, ĀB̄C, AB̄C̄, AB̄C (group of 4)

6c(iii) · 1 mark

  • 1 mark

    A + B̄

7a · 3 marks

  • 1 mark

    A digital certificate is an electronic/online document.

  • 1 mark

    used to authenticate/prove the identity of a website/the online identity of an individual/organisation

  • 1 mark

    typically issued by a CA

7b · 2 marks

  • 1 mark

    The digital certificate provides the public key

  • 1 mark

    … that can be used to validate the private key associated with the organisation/website/digital signature

8a · 3 marks

  • 1 mark

    (23) feature(sliding_doors).

  • 1 mark

    (24) available(sliding_doors, minivan).

  • 1 mark

    (25) unavailable(sliding_doors, hatchback).

8b · 1 mark

  • 1 mark

    (Options =) sunroof, reversing_camera

8c · 4 marks

  • 1 mark

    feature(F)

  • 1 mark

    bodystyle(B)

  • 1 mark

    unavailable(F, B)

  • 1 mark

    all correct Boolean operators and punctuation (allow , for AND) and no additional lines of code

9 · 3 marks

  • 1 mark

    Deep learning learns by finding hidden patterns that are undetectable to humans.

  • 1 mark

    It structures algorithms in layers: input layer, hidden layers and output layer.

  • 1 mark

    … to create an artificial neural network to learn and make intelligent decisions on its own.

10a · 1 mark

  • 1 mark

    The elements are sorted according to the compare function / in ascending / descending order.

10b · 5 marks

  • 1 mark

    Correct initialization of variables (e.g. TopOfList  1, EndOfList  100000, Found  FALSE, NotInList  FALSE)

  • 1 mark

    Correct loop condition WHILE Found = FALSE AND NotInList = FALSE

  • 1 mark

    Correct calculation CurrentItem  (TopOfList + EndOfList) DIV 2

  • 1 mark

    Correct IF-ELSE conditions for found and list boundary checks

  • 1 mark

    Correct pointers adjustment TopOfList  CurrentItem + 1 / EndOfList  CurrentItem – 1

10c · 2 marks

  • 1 mark

    Big O for a binary search is O(Log₂ n) // Big O notation is used to indicate the time/space complexity of an algorithm.

  • 1 mark

    The time taken to complete the search increases logarithmically as the number of search items increases linearly // The time taken to complete the search increases linearly as the number of search items increases exponentially // As the search field is repeatedly getting smaller, the number of comparisons made before the item is found, or the number of items runs out, is relatively small.

11a · 2 marks

  • 1 mark

    Uses hard-wired code/control units / Uses relatively few instructions / simple instructions / Uses relatively few addressing modes

  • 1 mark

    Makes use of a single-cycle for each instruction / fixed length / fixed format instructions / general-purpose registers / Pipelining is straightforward to apply / The design emphasis is on the software / Processor chips require few transistors.

11b · 3 marks

  • 1 mark

    Once the processor detects an interrupt at the start/end of the fetch-execute cycle

  • 1 mark

    … the current program is temporarily stopped and the status of each register stored on the stack.

  • 1 mark

    After the interrupt has been serviced/the Interrupt Service Routine (ISR) has been executed … // … the registers can be restored to its original status before the interrupt was detected // … the data can be restored from the stack.

11c · 3 marks

  • 1 mark

    Pipelining adds an additional complexity // there could be a number of instructions still in the pipeline when the interrupt is received

  • 1 mark

    All the instructions currently in operation are usually discarded except for the last one/the one at write back

  • 1 mark

    … the interrupt handler routine is applied to the remaining instruction. // Once the interrupt has been serviced the processor can restart with the next instruction in the sequence.

Questions

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  3. 3
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  4. 4
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  5. 5
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  6. 6
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  8. 8
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  9. 9
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  10. 10
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  11. 11
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