Computer Science 9618/12 October/November 2024: question paper and mark scheme
Cambridge AS & A Level Computer Science (9618), Paper 1 Theory Fundamentals, October/November 2024. Read both free below, or download them. Done the paper? Get it marked by AI against this mark scheme.
(a) Complete the truth table for the logic expression:
X = (A XOR B) NAND (A AND (B XOR C))
Working space
A B C X
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1
[2]
(b) Draw the logic circuit for the logic expression:
W = P NAND ((Q OR NOT R) XOR (P XOR Q))
P
Q W
R
[2]
Mark scheme
1(a) 1 mark for each shaded part. 2
A B C X
0 0 0 1
0 0 1 1
0 1 0 1
0 1 1 1
1 0 0 1
1 0 1 0
1 1 0 1
1 1 1 1
1(b) 1 mark for (P XOR Q) and (Q OR NOT R) 2
1 mark for second XOR gate and final NAND gate with appropriate inputs
Embedded systems are used in many electronic devices.
(a) Describe the drawbacks of embedded systems.
…… [3]
(b) An embedded system has Dynamic RAM (DRAM).
Identify one benefit of using DRAM instead of Static RAM (SRAM) in an embedded system.
…… [1]
(c) Give two differences between Erasable Programmable ROM (EPROM) and Electrically
Erasable Programmable ROM (EEPROM).
Difference 1 ……
Difference 2 ……
[2]
Mark scheme
2(a) 1 mark for each bullet point (max 3) 3
e.g.
• It is difficult to change / update the firmware by the user
• Errors cannot be fixed easily // Troubleshooting / fault-finding / repairing is
a specialist task / expensive
• Functionality cannot be changed/extended easily // Cannot be easily
adapted for another task
• Faulty / outdated devices are often thrown away rather than repaired
• … leading to e-waste
2(b) 1 mark from: 1
• DRAM is less expensive to manufacture/purchase than SRAM in the
embedded system
• DRAM has a higher bit density per chip // more data can be stored
per chip
2(c) 1 mark for each bullet point (max 2) 2
• EPROM uses ultraviolet light to erase data whilst EEPROM uses an
electrical signal to do this
• EPROM has to be removed from the circuit board when changing the
data whilst EEPROM remains in the circuit when the data is changed
• EPROM erases all the data, EEPROM can erase parts of the data
A student has a computer.
(a) The computer is designed using the Von Neumann model for a computer system.
Complete the table by describing the purpose of each of the given registers.
Register Purpose
Program Counter
(PC) ……
Memory Address
Register (MAR) ……
Memory Data
Register (MDR) ……
Index Register (IX)
[4]
(b) The student needs to connect the computer to a monitor that has a screen resolution of
2560 × 1600 pixels. The monitor also has built-in speakers.
The computer has a Video Graphics Array (VGA) port and a High Definition Multimedia
Interface (HDMI) port.
Explain the benefits of connecting the monitor to the computer using the HDMI port instead of the VGA port.
…… [4]
(c) The computer has an Operating System (OS). One of the key management tasks of the OS is process management.
Describe the process management tasks performed by an OS.
…… [4]
Mark scheme
3(a) 1 mark for each correct purpose 4
Register Purpose
Program Counter Stores the address of the next instruction to be
(PC) fetched/executed
Memory Address Stores the address of the memory location
Register (MAR) where data will be read from/written to
Stores the data read from the address in the
Memory Data
MAR // stores the data to be written to the
Register (MDR)
address in the MAR
Stores a number that will be added to the
Index Register (IX)
operand, to form the address of the data
3(b) 1 mark for each bullet point (max 4) 4
e.g.
• HDMI has faster transfer rates than VGA
• … needed due to high resolution / large number of pixels of monitor //
HDMI supports the high resolution of the monitor
• HDMI supports video and audio transfer between computer and
monitor speakers
• … so no separate sound cable is needed unlike VGA
• HDMI is digital interface therefore no data is lost in transfer to analogue
and back
• HDMI is less prone to error/crosstalk/external interference
3(c) 1 mark for each bullet point (max 4) 4
e.g.
• It manages the scheduling of processes // Decides which process is to be
run next
• Allows multi-tasking/multi-processing
• Ensures fair access
• Handles interrupts
• Manages / allocates which resources the processes require
• Facilitates the sharing and exchange of data between processes
• Prevents interference between processes // conflict resolution
A program is written in a high-level language by a team of three programmers using an Integrated
Development Environment (IDE).
(a) Describe how the programmers can use the debugging features of a typical IDE during the development of the program.
…… [4]
(b) The programmers created a new program library whilst developing the program.
Describe the benefits to the programmers of creating a program library.
…… [3]
(c) The file containing the final program code will be sent by email for beta testing.
Identify one security method that can be used to protect the program code from unauthorised access during email transfer.
Explain how your chosen method protects the program code.
Security method ……
Explanation ……
[3]
Mark scheme
4(a) 1 mark for each bullet point (max 4) 4
e.g.
• Single stepping
• Run the program one line at a time
• … and check the variable contents / program flow // show the effect of
each line of code
• Set breakpoints
• … run the code up to a set line
• ... and then check the status
• Variable/report watch window
• … view how the data changes as the program is running
4(b) 1 mark for each bullet point (max 3) 3
e.g.
• Subroutines can be shared / reused
• … between team members who are working independently
• … without having to rewrite/re-test them which saves the
programmers’ time
• A program library provides continuity between programs/programmers
• Individual programmers can contribute their specialisms to the library //
Individual programmers can use the specialisms of others
4(c) 1 mark for the security method. 2 marks for explanation 3
Security method:
Encryption
Explanation
• File contents are converted to cipher text
• If intercepted the data cannot be understood without the decryption key
A computer programmer is learning about the importance of acting ethically at work.
(a) Explain the reasons why the computer programmer needs to act ethically towards colleagues and the public.
Colleagues ……
The public ……
[4]
(b) The programmer writes a program to be used in a business. The source code of the program
can be modified by the business. The business pays the programmer for the maintenance and security updates.
(i) Identify one suitable type of software licence for the program and describe the reasons for your choice.
Type of software licence ……
Reasons for choice ……
[3]
(ii) Explain the reasons why the programmer should copyright their program.
…… [2]
Mark scheme
5(a) 1 mark for each bullet point max 2 for public max 2 for colleagues 4
e.g.
Colleagues:
The programmer should:
• Treat colleagues fairly and avoid acts of discrimination
• Be prepared to accept / offer critique
• … so that technical work can be improved
• Credit the contributions of colleagues
• … so that they feel valued / respected
• Help / train colleagues
etc.
e.g.
The public:
The programmer should:
• Maintain the health, safety and welfare of the public
• … so as not to endanger anyone
• Be honest / realistic in making claims about the software
• … so that public trust is maintained
• Maintain the security of the public's data
etc.
5(b)(i) Type of software licence 3
1 mark for
• Open Source Initiative // Free Software Foundation
Reason for choice:
1 mark for each bullet point (max 2)
• Allows program source code to be examined
• … so that the business can adapt/modify the program to meet their needs
• Allows the programmer to earn money for the software and updates
5(b)(ii) 1 mark for each bullet point (max 2) 2
• To identify themselves as the owner/author // To gain formal recognition
of ownership
• To allow for legal consequences if anyone steals/copies it
• To restrict competition
A company uses a relational database to store data about its customers, employees and the individual repair jobs that customers have booked.
(a) Explain the benefits of using a relational database instead of a file-based approach.
…… [3]
(b) The company decides which employees will work on each repair job. An employee can log into the database to access information about their repair jobs.
The database is normalised and includes these tables:
• CUSTOMER stores personal data about each customer
•
EMPLOYEE stores personal data about each employee
• LOGIN_DATA stores the username and password for each employee
• JOB stores the data about each repair job
• JOB_EMPLOYEE stores the employees that are working on each repair job.
(i) Identify each relationship between the database tables and explain how each relationship can be implemented in the normalised database.
…… [6]
(ii) The database also has the table INVOICE that stores data about each invoice that is sent to a customer.
Example data from the table INVOICE is given.
InvoiceID DateSent Amount Paid JobID
29262 12/12/2023 105.20 Y 221
26765 11/11/2023 200.00 Y 315
13290 02/01/2024 50.00 Y 315
34090 05/02/2024 25.95 N 569
Write a Structured Query Language (SQL) script to return the total amount of all the invoices sent in the year 2023 that have been paid.
…… [3]
Mark scheme
6(a) 1 mark each to max 3 3
e.g.
• There is reduced data redundancy // less repeated data
• … because each item of data is only stored once
• Data consistency is maintained // Data integrity is improved
• … changes in one table will automatically update in another
• ... linked data cannot be entered differently in two tables
• Program-data independence is ensured
• … changes to the data do not require programs to be re-written // queries
are not dependent on the structure of the data
• Complex queries are easier to run
• Different views can be provided
• …. so users can only see specific aspects of the database
• Multiple concurrent access is possible
• ... through record locking
6(b)(i) 1 mark each to max 6 6
• CUSTOMER to JOB is 1 to many
• … implemented by Primary Key in CUSTOMER is Foreign Key in JOB
• EMPLOYEE to LOGIN_DATA is 1 to 1
• … implemented by Primary Key in EMPLOYEE is Foreign Key in
LOGIN_DATA
• JOB to JOB_EMPLOYEE is 1 to many
• … implemented by Primary Key in JOB is Foreign Key in
JOB_EMPLOYEE
• EMPLOYEE to JOB_EMPLOYEE is 1 to many
• … implemented by Primary Key in EMPLOYEE is Foreign Key in
JOB_EMPLOYEE
6(b)(ii) 1 mark each 3
• Select SUM of Amount
• From the correct table and one correct condition
• Remaining correct condition
Example:
SELECT SUM(Amount)
FROM INVOICE
WHERE Paid = "Y"
AND DateSent >= #01/01/2023# AND DateSent <=
#31/12/2023#
A student takes a photograph of a science experiment.
(a) The photograph is saved as a bitmapped image.
(i) Define the following bitmap terms.
Colour depth ……
File header ……
[2]
(ii) Explain why changing the image resolution will affect the image quality and file size.
Image quality ……
File size ……
[2]
(iii) Identify one lossless method of compressing an image.
…… [1]
(b) The student draws a picture on paper that is scanned into the computer and saved as a
vector graphic.
Define the vector graphic terms property and drawing list.
Property ……
Drawing list ……
[2]
Mark scheme
7(a)(i) 1 mark for each correct definition 2
Colour depth:
• the number of bits used to represent a colour // the number of colours that
can be represented in an image
File header:
• stores data about the image file / metadata
7(a)(ii) 1 mark for each correct explanation 2
Image quality:
• Decreasing resolution means details within the image are lost because
there are fewer pixels // Increasing resolution means the image is more
detailed because there are more pixels
File size:
• Decreasing the resolution will decrease the file size because there are
fewer pixels therefore less data // Increasing the resolution will increase
the file size because there are more pixels therefore more data
7(a)(iii) 1 mark for correct method 1
For example:
• Run-Length Encoding
7(b) 1 mark for each correct definition 2
Property:
• an attribute of a drawing object // data about a shape // defines one
aspect of the appearance of a drawing object
Drawing list:
• all the drawing objects/shapes in an image // stores the
commands/descriptions / mathematical equations required to draw
each object
The following table shows part of the instruction set for a processor. The processor has two registers, the Accumulator (ACC) and the Index Register (IX).
Instruction
Explanation
Opcode Operand
LDM #n Immediate addressing. Load the number n to ACC
LDD <address> Direct addressing. Load the contents of the location at the given address to ACC
LDI <address> Indirect addressing. The address to be used is at the given address.
Load the contents of this second address to ACC
LDX <address> Indexed addressing. Form the address from <address> + the contents of the index register. Copy the contents of this calculated address to ACC
LDR #n Immediate addressing. Load the number n to IX
ADD #n/Bn/&n Add the number n to the ACC
ADD <address> Add the contents of the given address to the ACC
SUB #n/Bn/&n Subtract the number n from the ACC
SUB <address> Subtract the contents of the given address from the ACC
INC <register> Add 1 to the contents of the register (ACC or IX)
DEC <register> Subtract 1 from the contents of the register (ACC or IX)
<address> can be an absolute or a symbolic address
# denotes a denary number, e.g. #123
B denotes a binary number, e.g. B01001010
& denotes a hexadecimal number, e.g. &4A
(a) The current contents of memory are shown:
Address Data
19 25
20 23
21 2
22 4
23 15
24 50
25 22
The current contents of the ACC and IX are shown:
ACC 50
IX 20
Complete the table by writing the content of the ACC and the IX after each set of instructions has run.
Instructions ACC content IX content
LDM #19
1
DEC ACC
LDD 23
2
ADD 19
LDI 25
3
INC ACC
LDR #21
4
LDX 2
[5]
(b) The instruction set also includes these bit manipulation instructions:
Instruction
Explanation
Opcode Operand
AND #n/Bn/&n Bitwise AND operation of the contents of ACC with the operand
Bitwise AND operation of the contents of ACC with the
AND <address> contents of <address>
XOR #n/Bn/&n Bitwise XOR operation of the contents of ACC with the operand
Bitwise XOR operation of the contents of ACC with the
XOR <address> contents of <address>
OR #n/Bn/&n Bitwise OR operation of the contents of ACC with the operand
Bitwise OR operation of the contents of ACC with the
OR <address> contents of <address>
Bits in ACC are shifted logically n places to the left. Zeros
LSL #n are introduced on the right-hand end
Bits in ACC are shifted logically n places to the right. Zeros
LSR #n are introduced on the left-hand end.
<address> can be an absolute or a symbolic address
# denotes a denary number, e.g. #123
B denotes a binary number, e.g. B01001010
& denotes a hexadecimal number, e.g. &4A
The current content of the ACC is shown:
ACC 1 0 0 1 1 0 1 0
(i) The table has three sets of instructions. The binary number 10011010 is reloaded into the ACC before each set of instructions is run.
Complete the table by writing the content of the ACC after each set of instructions has run.
Instructions ACC content
1 LSL #2
ADD #5
2
AND #30
OR B11110010
3
INC ACC
[3]
(ii) Explain how bit manipulation can be used to test whether the binary number stored in the ACC represents an odd denary number.
Write the bit manipulation instruction that will be used.
Explanation ……
Instruction ……
[3]
Mark scheme
8(a) 1 mark for each correct content of the ACC (4) 5
1 mark for correct IX column
Instructions ACC content IX content
LDM #19
1 18 20
DEC ACC
LDD 23
2 40 20
ADD 19
LDI 25
3 5 20
INC ACC
LDR #21
4 15 21
LDX 2
8(b)(i) 1 mark each correct content of ACC 3
Instructions ACC content
1 LSL #2 0110 1000
ADD #5
2 0001 1110
AND #30
OR B11110010
3 1111 1011
INC ACC
8(b)(ii) 1 mark each to max 2 for explanation 3
• An odd binary number will have a 1 in the Least Significant Bit (LSB)
• A bit manipulation operation is required to access/mask only the LSB and
clear all the others
• Compare the result of the masking with denary 1
• … the result of the comparison will be true if the number is odd
1 mark for correct instruction
• AND B00000001 // AND #1 // AND &01
A road bridge has a weight limit and a height limit for vehicles. For example, a vehicle must weigh less than 10 000 kg and must have a height of less than 3 m.
The bridge has a warning system. If a vehicle is approaching the bridge and it exceeds one or both limits, a sign displays a warning telling the driver of the vehicle to stop.
(a) The bridge warning system uses sensors to detect if a vehicle exceeds the limits.
Complete the table by identifying two different sensors that could be used by the system and describe how each sensor is used by the system.
Sensor Use in bridge warning system
[2]
(b) Explain whether the bridge warning system is an example of a monitoring system or of a control system.
…… [2]
Mark scheme
9(a) 1 mark for sensor and its use in this system 2
• Infra-red sensor
• Measure / check the height of the vehicle
• Pressure sensor
• Measure / check the weight of the vehicle
9(b) 1 mark for each bullet point (max 2) for a correct justification 2
No marks for the identification of the system
Monitoring system
• Because there is no use of feedback // the warning sign is only
an indicator
• ... the output of the turning on of the sign does not affect the input of data
from the sensors
• The system does not have any actuators
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On this page, free: the mark scheme for AS & A Level Computer Science 9618/12, October/November 2024 (9618_w24_ms_12), and the question paper (9618_w24_qp_12), to read or download, with each question's marking points written out underneath.
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Computer Science 9618/12 for October/November 2024 is out of 75 marks, with 1 hour 30 minutes to answer it.
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