PMT
Oxford Cambridge and RSA
Monday 10 June 2024 – Afternoon
A Level Computer Science
H446/01 Computer Systems
Time allowed: 2 hours 30 minutes
You can use:
* 9 9 0 3 6 5 1 5 3 6 *
• an HB pencil
Do not use:
• a calculator
* H 4 4 6 0 1 *
Please write clearly in black ink. Do not write in the barcodes.
Centre number Candidate number
First name(s)
Last name
INSTRUCTIONS
• Use black ink. You can use an HB pencil, but only for graphs and diagrams.
• Write your answer to each question in the space provided. If you need extra space use
the lined pages at the end of this booklet. The question numbers must be clearly shown.
• Answer all the questions.
INFORMATION
• The total mark for this paper is 140.
• The marks for each question are shown in brackets [ ].
• Quality of extended response will be assessed in questions marked with an asterisk (*).
• This document has 28 pages.
ADVICE
• Read each question carefully before you start your answer.
© OCR 2024 [601/4911/5] OCR is an exempt Charity
DC (PQ/JG) 326268/5 Turn over
, PMT
2
BLANK PAGE
PLEASE DO NOT WRITE ON THIS PAGE
© OCR 2024
, PMT
3
1 The stored program concept uses the Fetch-Decode-Execute cycle to get the next instruction
from memory and then execute it.
(a) Describe what happens during the fetch stage of the Fetch-Decode-Execute cycle.
You should state the different registers and buses that are used in your answer.
..........................................................................................................................................................
..........................................................................................................................................................
..........................................................................................................................................................
..........................................................................................................................................................
..........................................................................................................................................................
..........................................................................................................................................................
..........................................................................................................................................................
..................................................................................................................................................... [4]
(b) One of the instructions that may be fetched and executed as part of this cycle is a branch
instruction.
State the name of the register that would be altered in the execute phase during a branch
instruction.
..................................................................................................................................................... [1]
(c) Three ways of improving the performance of a CPU are increasing the clock speed, adding more
cores and using pipelining.
Explain how pipelining improves the performance of a CPU.
..........................................................................................................................................................
..........................................................................................................................................................
..........................................................................................................................................................
..........................................................................................................................................................
..........................................................................................................................................................
..................................................................................................................................................... [3]
© OCR 2024 Turn over
, PMT
4
(d) The Fibonacci sequence is a series of numbers. It starts with the number 0 and then 1. Each
number after that is a sum of the two numbers before it.
The first seven numbers in the series are:
0
1
1 (i.e. 1 + 0)
2 (i.e. 1 + 1)
3 (i.e. 1 + 2)
5 (i.e. 2 + 3)
8 (i.e. 3 + 5)
Orla has written some code to show the first five numbers in the Fibonacci sequence (0,1,1,2,3)
using the Little Man Computer (LMC) instruction set.
The LMC code that Orla has written contains an error.
START LDA MAX
BRZ END
LDA A
OUT
ADD B
STA B
LDA B
STA A
LDA MAX
SUB ONE
STA MAX
BRA START
END HLT
A DAT 0
B DAT 1
MAX DAT 5
ONE DAT 1
(i) State the five outputs that Orla’s code would give.
Output 1 ...........................................................................................................................................
Output 2 ...........................................................................................................................................
Output 3 ...........................................................................................................................................
Output 4 ...........................................................................................................................................
Output 5 ...........................................................................................................................................
[3]
© OCR 2024
Oxford Cambridge and RSA
Monday 10 June 2024 – Afternoon
A Level Computer Science
H446/01 Computer Systems
Time allowed: 2 hours 30 minutes
You can use:
* 9 9 0 3 6 5 1 5 3 6 *
• an HB pencil
Do not use:
• a calculator
* H 4 4 6 0 1 *
Please write clearly in black ink. Do not write in the barcodes.
Centre number Candidate number
First name(s)
Last name
INSTRUCTIONS
• Use black ink. You can use an HB pencil, but only for graphs and diagrams.
• Write your answer to each question in the space provided. If you need extra space use
the lined pages at the end of this booklet. The question numbers must be clearly shown.
• Answer all the questions.
INFORMATION
• The total mark for this paper is 140.
• The marks for each question are shown in brackets [ ].
• Quality of extended response will be assessed in questions marked with an asterisk (*).
• This document has 28 pages.
ADVICE
• Read each question carefully before you start your answer.
© OCR 2024 [601/4911/5] OCR is an exempt Charity
DC (PQ/JG) 326268/5 Turn over
, PMT
2
BLANK PAGE
PLEASE DO NOT WRITE ON THIS PAGE
© OCR 2024
, PMT
3
1 The stored program concept uses the Fetch-Decode-Execute cycle to get the next instruction
from memory and then execute it.
(a) Describe what happens during the fetch stage of the Fetch-Decode-Execute cycle.
You should state the different registers and buses that are used in your answer.
..........................................................................................................................................................
..........................................................................................................................................................
..........................................................................................................................................................
..........................................................................................................................................................
..........................................................................................................................................................
..........................................................................................................................................................
..........................................................................................................................................................
..................................................................................................................................................... [4]
(b) One of the instructions that may be fetched and executed as part of this cycle is a branch
instruction.
State the name of the register that would be altered in the execute phase during a branch
instruction.
..................................................................................................................................................... [1]
(c) Three ways of improving the performance of a CPU are increasing the clock speed, adding more
cores and using pipelining.
Explain how pipelining improves the performance of a CPU.
..........................................................................................................................................................
..........................................................................................................................................................
..........................................................................................................................................................
..........................................................................................................................................................
..........................................................................................................................................................
..................................................................................................................................................... [3]
© OCR 2024 Turn over
, PMT
4
(d) The Fibonacci sequence is a series of numbers. It starts with the number 0 and then 1. Each
number after that is a sum of the two numbers before it.
The first seven numbers in the series are:
0
1
1 (i.e. 1 + 0)
2 (i.e. 1 + 1)
3 (i.e. 1 + 2)
5 (i.e. 2 + 3)
8 (i.e. 3 + 5)
Orla has written some code to show the first five numbers in the Fibonacci sequence (0,1,1,2,3)
using the Little Man Computer (LMC) instruction set.
The LMC code that Orla has written contains an error.
START LDA MAX
BRZ END
LDA A
OUT
ADD B
STA B
LDA B
STA A
LDA MAX
SUB ONE
STA MAX
BRA START
END HLT
A DAT 0
B DAT 1
MAX DAT 5
ONE DAT 1
(i) State the five outputs that Orla’s code would give.
Output 1 ...........................................................................................................................................
Output 2 ...........................................................................................................................................
Output 3 ...........................................................................................................................................
Output 4 ...........................................................................................................................................
Output 5 ...........................................................................................................................................
[3]
© OCR 2024
