OCR A-Level Computer Science Computer systems (01), June 2025: Question 4

Question Answer Mark Guidance

4 (a) 1 correct answer = 1 mark 3

2 correct answers = 2 marks

5 correct answers = 3 marks

Description Command

Load the value stored in LDA / LOAD

the memory address into

the accumulator.

Branch without checking BRA / BR

the value in the

accumulator.

Store the value from the STA / STO

accumulator into the

memory address.

Branch if zero is in the BRZ / BZ

accumulator.

Branch if zero or a BRP / BP

positive number is in the

accumulator.

4 (b) 1 mark for each to max 4: 18 4 Accept alternative mnemonics from the spec: STO,

● Correctly inputting two values and storing at LOAD, BR, BZ, BP, IN, INPUT, COB, END.

least one value

● Correctly subtracting one number from the other If labels used must be a corresponding DAT location for

● Correct use of branch MP1.

● Correct output for each path

POSSIBLE SOLUTION:

INP

STA FIRST

INP

STA SECOND

SUB FIRST

BRP OUTPUTSECOND

LDA FIRST

OUT

HLT

OUTPUTSECOND LDA SECOND

OUT

HLT

FIRST DAT 0

SECOND DAT 0

4 (c) Mark Band 3 – High level (9-12 marks) 19

12 Answers may include, but are not limited to, some of

the points below:

The candidate demonstrates a thorough knowledge and

understanding of high/low level languages. The material AO1 Knowledge

is generally accurate and detailed. High Level Languages:

● Uses English-like syntax/words.

The candidate is able to apply their knowledge and ● Easier for humans to read, create and debug

understanding directly and consistently to the context ● Is problem orientated

provided. Evidence/examples will be explicitly relevant ● Not locked to any particular architecture (but needs

to the explanation. a translator for the given architecture)

● Programmer is not in control of what machine code

The candidate provides a thorough discussion which is instructions are generated by the translator.

well balanced. Evaluative comments are consistently

relevant and well-considered. Low level languages:

● Written in binary / 1s and 0s.

There is a well-developed line of reasoning which is ● Processor specific.

clear and logically structured. The information ● Programs are based around the instructions

presented is relevant and substantiated. available.

● Programmer has direct control over what

Mark Band 2 – Mid level (5-8 marks) instructions are being run and what memory is

being used.

The candidate demonstrates reasonable knowledge

● Provides an interface between programmer and

and understanding of high/low level languages. The

hardware.

material is generally accurate but at times

underdeveloped.

AO2 Application

The candidate is able to apply their knowledge and 1) This program could be written in a high level

understanding directly to the context provided although language. This is because it will most likely

one or two opportunities are missed. contain a user interface that makes various

Evidence/examples are for the most part implicitly network requests to fetch the news and then

present this to the user.

relevant to the explanation.

2) This program could be written in a low level

The candidate provides a sound discussion, the language as it is for an embedded system it

may have a novel architecture and have no

majority of which is focused. Evaluative comments are

translator. It would also need direct access to

the hardware and memory management.

for the most part appropriate, although one or two 3) This program could be written in a high level

opportunities for development are missed. language. This is because it will contain a user

interface that will most likely require a lot of

There is a line of reasoning presented with some functionality which can be simplified in a high

structure. The information presented is in the most part level language.

relevant and supported by some evidence. 4) This program could be written in either. Low

level would give direct access to the memory

Mark Band 1 – Low Level (1-4 marks) management to better handle large amounts of

data being processed. Higher level may have

The candidate demonstrates a basic knowledge of libraries for the data manipulation required.

some aspects of high/low level languages. The material 5) This program could be written in a low level

is basic and contains some inaccuracies. language. This is because it will need to have

direct access to the computer hardware to deal

The candidate makes a limited attempt to apply with memory allocation/deallocation, buffers,

acquired knowledge and understanding to the context data structures, registers, interrupts etc.

provided.

AO3 Evaluation

The candidate provides a limited discussion which is ● Low level languages allow you to direct access the

narrow in focus. Judgments if made are weak and devices resources such as the memory to allow you

unsubstantiated. The information is basic and to optimise the devices performance.

communicated in an unstructured way. ● Low level languages are commonly used in

embedded systems as they have limited resources

The information is supported by limited evidence and available.

the relationship to the evidence may not be clear. ● Low level languages are commonly used in real-

time systems when speed is a crucial factor

0 marks o Direct control of instructions means the

No attempt to answer the question or response is not ability to control the speed

worthy of credit. o Direct control over the memory addresses

used allows control of the memory footprint

● High level languages allow for faster development.

They contain built-in functions to write code quicker.

● High level languages are work across different

platforms so they can be run on different operating

systems.