Cambridge IGCSE™

* 5 0 1 5 4 0 7 3 5 7 *

COMPUTER SCIENCE 0478/12

Paper 1 Computer Systems February/March 2024

1 hour 45 minutes

You must answer on the question paper.

No additional materials are needed.

INSTRUCTIONS
● Answer all questions.
● Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs.
● Write your name, centre number and candidate number in the boxes at the top of the page.
● Write your answer to each question in the space provided.
● Do not use an erasable pen or correction fluid.
● Do not write on any bar codes.
● Calculators must not be used in this paper.

INFORMATION
● The total mark for this paper is 75.
● The number of marks for each question or part question is shown in brackets [ ].
● No marks will be awarded for using brand names of software packages or hardware.

This document has 16 pages. Any blank pages are indicated.

DC (DE) 327909/3
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1 Computers represent different types of data in binary.

(a) Tick (✓) one box to show the reason why computers use binary to represent data.

A Computers only allow 1s and 0s to be entered.

B Computers are made of switches and gates that can only be on or off.

C Binary does not need to be converted into other forms of data to be displayed.

D Both computers and humans can quickly process binary data.

[1]

(b) One form of data is characters.

The American standard code for information interchange (ASCII) denary number for the
character ‘N’ is 78.

(i) Tick (✓) one box to identify the ASCII denary number for the character ‘Q’.

A 81

B 80

C 79

D 77
[1]

(ii) Give the binary number for the ASCII denary number for ‘N’.

01001110
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Working space

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(iii) Explain how the word ‘RED’ is represented using a character set.
When each letter of the word is typed in, the CPU receives the signal of that letter in binary
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and looks up the equivalent value of that letter using the character set and displays it in
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text form
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(c) Sound can be represented as binary.

(i) Explain why recording sound with a higher sampling resolution creates a more accurate
recording.
There would be more approximations of the sound wave in binary value hence acheiving
...........................................................................................................................................
the closest possible sound wave to the one that was recorded
...........................................................................................................................................

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(ii) Give one other way that the accuracy of a sound recording can be improved.
Reduce background noise
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2 A computer has a central processing unit (CPU).

The CPU includes the registers:

• Program counter (PC)
• Memory address register (MAR)
• Memory data register (MDR)
• Accumulator (ACC)
• Current instruction register (CIR).

(a) The table contains five statements about the role of registers in the fetch–decode–execute
cycle of a CPU.

Letter Statement
A PC stores the address of the next instruction to be accessed
B MAR stores the instructions of the program that is running
C MDR stores the data passed to it from the PC
D ACC stores the result of each calculation
E CIR stores the instruction currently being executed

Two of the statements are not correct.

Identify the letter of each incorrect statement.

Suggest a corrected statement for each.

B
Incorrect statement 1 .........................................
MAR stores the address of the next instruction which is to be fetched
Corrected statement .................................................................................................................

...................................................................................................................................................

...................................................................................................................................................
C
Incorrect statement 2 .........................................
MDR stores the data passed to it from the main memory (RAM)
Corrected statement .................................................................................................................

...................................................................................................................................................

...................................................................................................................................................
[4]

(b) The computer has a single core 3.5 GHz processor and an 8 kB cache.

(i) State what is meant by a 3.5 GHz processor.

It performs the fetch-decode-execute cycle 3.5 billion times a second
...........................................................................................................................................

..................................................................................................................................... [1]

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(ii) The CPU is changed to a dual-core 3.5 GHz processor.

Explain how the number of cores affects the performance of a CPU.

The number of instructions that can be processed would increase. However, the processing
...........................................................................................................................................
speed may not increase as it will take longer to get to each core in the CPU
...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [2]

(iii) The amount of cache is increased to 64 kB.

Explain how the amount of cache affects the performance of a computer.

It increases the performance of the computer as more instructions can be stored in cache
...........................................................................................................................................
hence making it faster for the cpu to fetch instructions without having to fetch it from the
...........................................................................................................................................
main memory therefore saving time.
...........................................................................................................................................

..................................................................................................................................... [2]

(c) The computer has both primary and secondary storage.

(i) Random access memory (RAM) is one example of primary storage.

Describe what is meant by RAM.

It is a type of non-volatile memory storage that can be directly accessed by the cpu and can
...........................................................................................................................................
be used to store the current instructions and applications that the user is working on
...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [2]

(ii) Read only memory (ROM) is another example of primary storage. ROM often stores the
start-up instructions for a computer.

Identify one other item of data that is commonly stored in ROM.

...........................................................................................................................................

..................................................................................................................................... [1]

(iii) Some computers make use of virtual memory.

State the purpose of virtual memory.

To make space for more programs to be used at a time when the RAM is full
...........................................................................................................................................

..................................................................................................................................... [1]

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3 A computer has an operating system (OS).

(a) Complete the table by writing each missing OS function name and description.

Function name Description

……………………………………………………………………………

……………………………………………………………………………
managing memory
……………………………………………………………………………

……………………………………………………………………………

……………………................…
allows application software to run on the computer
……………………................…

……………………………………………………………………………

……………………………………………………………………………
managing peripherals
……………………………………………………………………………

……………………………………………………………………………

[3]

(b) The OS handles interrupts.

(i) State the purpose of an interrupt.

To inform the cpu that something is wrong
...........................................................................................................................................

..................................................................................................................................... [1]

(ii) Identify one input device and one example of an interrupt that it can generate.
Mouse
Input device .......................................................................................................................
The USB is not properly connected
Interrupt .............................................................................................................................
[1]

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(iii) A processor is currently executing a program. The processor receives an interrupt.

Explain how the processor manages the current program and the interrupt.

...........................................................................................................................................

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4 A student enters a uniform resource locator (URL) into their web browser.

Draw and annotate a diagram to show the process from the user entering the URL to the web
browser displaying the web page.

[5]

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5 Complete the description of digital currencies using the terms provided.

blockchains changed datachains decentralised

deleted encryption passport physical address

physically records time-stamp traced

transaction-chains virtually

Physically
A digital currency does not exist ........................................................... , it can only be accessed

electronically.
blockchains
Some digital currencies have digital ledgers called ........................................................... .

These are decentralised databases where each transaction is stored as a new set of data with
time-stamp
a ........................................................... and is linked to the previous set of data. This means that

transactions cannot be altered, only new transactions added, which allows the location of the data
traced
to be ........................................................... .
[4]

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6 A self-driving tractor sows seeds and harvests crops for a farmer. The self-driving tractor moves
automatically through the field, turning at each end and stopping when it has finished.

(a) One reason the self-driving tractor is a robot is because it has a mechanical structure that
includes wheels, an engine, and a framework.

Give one other reason why the self-driving tractor is an example of a robot.
It is automatically operated
...................................................................................................................................................

............................................................................................................................................. [1]

(b) If a person is detected within 3 metres whilst the tractor is moving, the self-driving tractor
must stop.

(i) Explain how an infra-red sensor, microprocessor and actuator can be used to stop the
self-driving tractor if a person is detected within 3 metres.
The infra-red sensor takes continuous readings of the overall temperature of the surroundings.
...........................................................................................................................................
.
The sensor takes readings in analogue form and must be converted via and ADC
...........................................................................................................................................
(Analogue to Digital Converter) in order to be understood by the microprocessor. The
...........................................................................................................................................
microprocessor then takes in the readings and compares them with a preset value stored.
...........................................................................................................................................
If the values are greater than the preset value, a signal is sent from the microprocessor to the
...........................................................................................................................................
actuator which then hence causes the tractor to stop. Otherwise, nothing happens and the
...........................................................................................................................................
process is continuous
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(ii) Identify one other sensor that the self-driving tractor might use and how it will use the
sensor.
Proximity sensor
Sensor ...............................................................................................................................
To detect any motion within a given preset range
Use ....................................................................................................................................

...........................................................................................................................................
[2]

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(c) Explain the drawbacks of a farmer using a self-driving tractor to sow seeds and harvest crops.

...................................................................................................................................................

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(d) The self-driving tractor has an in-built expert system that the farmer can use to solve any
errors with the tractor.

Identify three components of an expert system.

User interface
1 ................................................................................................................................................
Knowledge base
2 ................................................................................................................................................
Inference engine
3 ................................................................................................................................................
[3]

(e) At the end of each day the self-driving tractor transmits the data it has collected to the farmer’s
computer in their house.

The transmission uses an echo check.

(i) Describe the role of the self-driving tractor and the farmer’s computer in the echo check.
The self-driving tractor and the farmers computer both agree that a certain criteria must be
...........................................................................................................................................
met. The self-driving tractor transmits the data to the farmer's computer. If the criteria is met,
...........................................................................................................................................
then the data is error-free, otherwise the data is re-sent back to the self-driving tractor. And the
...........................................................................................................................................

...........................................................................................................................................
data is re-sent again to the farmer's computer.

...........................................................................................................................................

..................................................................................................................................... [3]

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(ii) Another method of error checking is a parity block check.

The table shows 7 bytes that are transmitted using odd parity. The parity bit has been
completed for each byte.

Complete the parity byte for the data.

parity
bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1
bit

byte 1 1 1 0 0 1 1 1 0

byte 2 1 0 0 0 0 1 1 0

byte 3 0 1 0 0 0 0 0 0

byte 4 0 1 0 0 1 1 1 1

byte 5 1 0 0 0 0 0 0 0

byte 6 0 1 1 1 1 1 1 1

byte 7 1 1 0 0 1 1 0 1

parity
byte
[3]

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7 Data is transmitted using the internet.

(a) The data is encrypted before transmission.

(i) State the purpose of encrypting data.

To secure the data from being understood by a hacker
...........................................................................................................................................

..................................................................................................................................... [1]

(ii) Describe the differences between symmetric and asymmetric encryption.

...........................................................................................................................................

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(b) The data is transmitted using packet switching.

(i) Identify two items of data contained in a packet header.

The IP address of the sender and receiver
1 ........................................................................................................................................

The sequence order

2 ........................................................................................................................................
[2]

(ii) Give the purpose of a router in the packet-switching process.

To re-route each data packet into its right node
...........................................................................................................................................

..................................................................................................................................... [1]

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8 (a) Hexadecimal can be used to represent binary numbers.

(i) Convert the denary number 236 into hexadecimal.

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Working space

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(ii) Give one benefit of using hexadecimal instead of binary to represent data.
It can be more easily understood
...........................................................................................................................................

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(b) Two’s complement can be used to represent positive and negative binary integers.

(i) Convert the two’s complement integer 10110111 into denary.

Show all your working.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

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(ii) Convert the denary number 45 into an 8-bit two’s complement integer.

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Working space

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(c) Logical shifts are performed on binary integers.

State the mathematical effect of a right shift of four places on a positive binary integer.

...................................................................................................................................................

...................................................................................................................................................

............................................................................................................................................. [2]

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