Computer Science 9618/13 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) Describe the operation of a 2-input XOR gate.
…… [1]
(b) Write the logic expression for the following logic circuit.
A
X
B
C
X = ……
…… [2]
(c) Draw the logic circuit for the logic expression:
X = ((NOT A AND (B AND C)) OR (B NAND C)) AND NOT A
A
B X
C
[2]
Mark scheme
1(a) 1 mark for: 1
Output is only 1 if one input is 1 and the other is 0 // Output is only 1 if both
inputs are different // Output is only 0 if both inputs are the same
1(b) 1 mark each: 2
• ((A NOR B) AND (A OR B))
• NAND (B AND C)
X = ((A NOR B) AND (A OR B)) NAND (B AND C)
1(c) 1 mark for NOT gate, 2 correct AND gates and the NAND gate 2
1 mark for OR gate and the final AND gate
A memory buffer uses Dynamic RAM (DRAM).
(a) Identify two differences between DRAM and Static RAM (SRAM).
Difference 1 ……
Difference 2 ……
[2]
(b) Explain how a memory buffer is used when a computer is transferring data to its magnetic hard disk drive.
…… [4]
Mark scheme
2(a) 1 mark for each difference 2
e.g.
• DRAM requires constant refreshing, but SRAM does not need to be
constantly refreshed
• DRAM generally has greater capacities per chip, but SRAM generally has
lower capacities per chip
• DRAM has slower access times than SRAM
2(b) 1 mark for each bullet point (max 4) 4
• The computer and the hard disk drive transmit and receive at different
speeds // The computer transfers data faster than the HDD can receive
• The buffer is used for temporary storage
• … so that the computer can transfer data to the buffer at the higher speed
• ... and is not held up waiting for data to transfer
• … and so that data is transferred to hard disk drive from the buffer at the
slower rate
A car has an automatic braking system.
A sensor is used to measure the distance to objects that are in front of the car.
The car automatically brakes if an object is too close to the front of the car or the distance between the car and the object is decreasing too quickly. The closer the object is to the front of the car, the harder the car brakes so that the car slows down more quickly.
Explain the reasons why the automatic braking system of the car is a control system.
…… [3]
Mark scheme
3 1 mark for each bullet point (max 3) 3
• The system uses feedback
• The system acts independently
• Input data causes the car to brake
• … braking decreases the/changes the distance to the object
• … this new distance is used to determine whether/how hard the car
needs to brake
A company makes ice cream and sells it to shops.
The ice cream is made in batches: a large quantity of one type and flavour of ice cream that is then split into smaller quantities for sale.
The company’s owner has designed a relational database, ICECREAM, to store data about their ice cream and customers.
Some of the tables in the database are given. The database is not normalised.
BATCH(BatchID, Type, Flavour, Size, SellingPrice, EndDate)
CUSTOMER(CustomerID, CompanyName, EmailAddress, TelephoneNumber)
SALE(SaleID, BatchID, CustomerID, Quantity, Date)
(a) Identify two foreign keys in the table SALE and the table that each foreign key references.
Foreign key 1 ……
Table name 1 ……
Foreign key 2 ……
Table name 2 ……
[2]
(b) Write an SQL script to return the total quantity of ice cream sold to the customer with the ID of
0034E in the year 2023.
…… [3]
(c) The table definition for BATCH is repeated here:
BATCH(BatchID, Type, Flavour, Size, SellingPrice, EndDate)
Sample data for the table BATCH is given:
BatchID Type Flavour Size SellingPrice EndDate
KlV12 Plain Vanilla 1 2.20 12/12/2024
RlC14 Plain Chocolate 0.5 1.80 12/12/2024
TYL1 Non-dairy Lemon 0.5 2.10 01/02/2025
FYV2 Non-dairy Vanilla 0.25 1.50 02/02/2025
BIV13 Plain Vanilla 1 2.20 02/02/2024
(i) Write an SQL script to define the table BATCH.
Include constraints (restrictions) on the data that can be entered into each field where appropriate.
(ii) The table BATCH is not normalised.
Normalise the database table BATCH.
Write the table definitions for your new tables.
Identify any primary and foreign keys in your tables.
Do not change or include the tables CUSTOMER and SALE.
…… [4]
(d) Complete the following table by defining each database term.
Database term Definition
Entity
Attribute
[2]
(e) A Database Management System (DBMS) supports data integrity.
Explain how a DBMS supports data integrity.
…… [3]
Mark scheme
4(a) 1 mark each: 2
• Foreign key: BatchID, table BATCH
• Foreign key: CustomerID, table CUSTOMER
4(b) 1 mark each: 3
• SELECT SUM(Quantity)
• FROM SALE WHERE and one correct condition
• AND with remainder correct conditions
e.g.
SELECT SUM(Quantity)
FROM SALE
WHERE CustomerID = "0034E"
AND Date >= #01/01/2023# AND Date <= #31/12/2023#;
4(c)(i) 1 mark for each bullet point 5
• Create table BATCH with opening and closing brackets, all statements
within brackets
• BatchID, Type and Flavour as varchar or equivalent
• …with suitable constraint(s)
• Size as decimal, SellingPrice as currency, EndDate as date (or
equivalent)
• Primary key identified as BatchID
e.g.
CREATE TABLE BATCH(
BatchID VARCHAR(6) NOT NULL,
Type VARCHAR (20) NOT NULL,
Flavour VARCHAR (20) NOT NULL,
Size FLOAT,
SellingPrice CURRENCY,
EndDate DATE,
PRIMARY KEY(BatchID)
);
4(c)(ii) 1 mark for each bullet point each (max 4) 4
e.g.
• Ice cream table with an appropriate name
• … containing type, flavour, size, selling price
• … with suitable primary key
• … foreign key identified in BATCH that links to the primary key in
ICECREAM
Example table definitions – not example answer:
BATCH(BatchID, IceCreamID, EndDate)
ICE_CREAM(IceCreamID, Type, Flavour, Size,
SellingPrice)
4(d) 1 mark for each definition 2
Entity:
• A real-life object that is represented as a table
Attribute:
• An item of data about an entity
4(e) 1 mark for each bullet point each (max 3) 3
• Referential integrity is enforced
• … such as cascade update/delete // if the data is changed in one place it
is updated in every other place
• ... and ensures each foreign key has a corresponding primary key
A computer programmer writes programs that are distributed with a software licence.
(a) Complete the table by writing the type of software licence each statement describes.
Statement Software licence
A fee is charged for the software. The source
code cannot be accessed. Users do not get a free trial.
Users can try the software before buying it.
Users may not be able to access all features during the trial.
Software is usually free of charge. Users can
access the source code and alter the program to their needs.
[3]
(b) Explain the reasons why it is important for the computer programmer to join a professional ethical body.
…… [3]
Mark scheme
5(a) 1 mark for each correct licence 3
Statement Software Licence
A fee is charged for the software. The source code
Commercial
cannot be accessed. Users do not get a free trial.
Users can try the software before buying it. Users
Shareware
may not be able to access all features during the trial.
Software is usually free of charge. Users can access Open Source //
the source code and alter the program to their needs. Free software
5(b) 1 mark for each bullet point (max 3) 3
e.g.
• The professional ethical body has ethical guidelines to follow
• … so clients/other staff know the standards being applied
• … so the computer programmer does not have to decide what is ethical
it's written down
• Clients/staff know the computer programmer is reputable
• … there may be a test/requirement for entry
• … giving recognition of the computer programmer's skills/knowledge
• The professional ethical body provides help and support
• … for example, if the computer programmer needs legal advice
• The professional ethical body runs training courses
• … to keep the computer programmer's skills up to date
A computer system stores text, images and sound.
(a) A character set is used to represent characters in a computer.
Identify and describe one character set.
Character set ……
Description ……
[2]
(b) The colour of each pixel in a bitmapped image is represented by 8 bits.
(i) State the largest number of different colours that can be represented by 8 bits.
…… [1]
(ii) State one drawback of increasing the number of bits that represents each pixel in the bitmap image.
…… [1]
(iii) A bitmap image can be compressed using lossy compression.
Explain the reasons why lossy compression is often suitable for a bitmap image.
…… [2]
(c) (i) Explain how an analogue sound wave is converted into digital data.
…… [2]
(ii) Describe one method of compressing a sound file using lossy compression.
…… [2]
Mark scheme
6(a) 1 mark for identification 1 mark for matching description 2
e.g.
• ASCII
• 7/8 bits per character // represents 128/256 characters // represents all
characters from Latin alphabet
• UNICODE
• 8/16/32 bits per character // represents 256/65536+ characters //
represents all characters in all languages
6(b)(i) 1 mark for: 1
256 // 28
6(b)(ii) 1 mark for: 1
Increased file size
6(b)(iii) 1 mark for each bullet point (max 2) 2
e.g.
• The change may not be noticeable // Data removed is usually not noticed
by the human eye
• … for example, changes in shade/detail
• It produces a larger decrease in file size compared to lossless // Lossy
decreases file size considerably
6(c)(i) 1 mark for each bullet point (max 2) 2
• Value/magnitude/size of the analogue sound wave is measured a set
number of times each second/time / at set intervals
• Each sample/reading/measurement is given the binary number and
stored in sequence
6(c)(ii) 1 mark for each correct point and 1 mark for matching expansion 2
e.g.
• Decrease sample rate
• … fewer samples/readings/measurements stored per second // fewer bits
per second stored
• Decrease sample resolution
• … fewer bits per sample/reading/measurement // each sample has
fewer bits
• Sound outside of set/human hearing range is removed
• … fewer measurements are stored / decreases the number of possible
binary values so fewer bits are stored
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
Direct addressing. Load the contents of the location at the given
LDD <address> address to ACC
Indirect addressing. The address to be used is at the given
LDI <address> address.
Load the contents of this second address to ACC
Indexed addressing. Form the address from <address> + the
LDX <address> 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
50 54
51 55
52 50
53 52
54 100
55 25
56 50
The current contents of the ACC and IX are shown:
ACC 50
IX 45
Complete the table by writing the content of the ACC after each program has run.
Instructions ACC content
LDD 50
1 ADD #4
ADD 54
LDI 53
2 DEC ACC
ADD 56
LDM #55
3
SUB #5
[3]
(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 contents
AND <address> 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 contents
XOR <address> 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 contents of
OR <address>
<address>
<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
Explain how bit manipulation can be used to clear the data in an 8-bit register.
Write the bit manipulation instruction that will be used.
Explanation ……
Instruction ……
[3]
Mark scheme
7(a) 1 mark each: 3
Instructions ACC content
LDD 50
1 ADD #4 158
ADD 54
LDI 53
2 DEC ACC 99
ADD 56
LDM #55
3 50
SUB #5
7(b) 1 mark for each bullet point for the explanation 3
1 mark for correct instruction
• A bit manipulation operation is required to set all the bits to zero
• Compare the result of the masking with 0
• … the result of comparison will be true if the register is cleared
• AND B00000000 / #00 / &00
(a) Convert the hexadecimal number 1FAB into denary.
Working ……
Denary value …… [1]
(b) Explain how to convert the two’s complement integer 10011111 into denary. Give the denary
value after conversion.
Explanation ……
Denary value ……
[3]
(c) Describe the difference between a right logical binary shift and a right arithmetic binary shift.
…… [2]
Mark scheme
8(a) 1 mark for: 1
Denary value: 8107
8(b) 1 mark for each bullet point for the method (max 2) 3
e.g.
• Flip each bit then add 1 …
• … method of converting the new binary number into denary
• Most significant 1 bit is treated as the corresponding negative
denary value …
• … add the other positive corresponding denary values
1 mark for correct conversion
Denary value: −97
8(c) 1 mark each: 2
• A logical shift moves all bits to the right and inserts zeros in the
appropriate leftmost bits
• An arithmetic shift moves all bits to the right but copies the sign bit into
the Most Significant Bit (MSB)
A computer is connected to a Local Area Network (LAN) that connects to a Wide Area Network
(WAN).
(a) Describe the characteristics of a WAN.
…… [2]
(b) Copper cable can be used to transmit data in a network.
Complete the table by identifying and describing two other transmission media that can be used to transfer data in the WAN.
Transmission medium Description
[4]
(c) The computer on the LAN is used for real-time video conferences, where people connected to the internet communicate in real-time using video and audio.
Explain how bit streaming is used in a real-time video conference.
…… [4]
(d) The LAN has a router. The router has a public IP address and a private IP address.
(i) State the purpose of a public IP address and a private IP address.
Public IP address ……
Private IP address ……
[2]
(ii) The LAN uses subnetting.
Describe the purpose of subnetting in a network.
…… [2]
Mark scheme
9(a) 1 mark for each bullet point (max 2) 2
• A WAN covers a large geographical area
• External/public infrastructure is used
• Non-dedicated hardware
9(b) 1 mark for correct media 1 mark for matching description e.g. 4
• Fibre optic
• Transmits data as pulses of light
• Radio waves / microwaves
• Transmits electromagnetic waves on different frequencies
9(c) 1 mark for each bullet point (max 4) 4
• Data is compressed before transmitting
• The video and audio are transmitted continuously as a series of bits
• The video is uploaded to a media server
• On download, the media server sends the data to a buffer
• The buffer stores data from server until the receiving device can
process it
• The receiving device receives the bit stream from the buffer
9(d)(i) 1 mark for public IP address and 1 mark for private IP address: 2
Public IP address:
• So that the router is visible to the Internet/external network/WAN
Private IP address:
• So that the router is identified to computers within the LAN
9(d)(ii) 1 mark for each bullet point (max 2) 2
• It allows the network to be divided into smaller networks
• … which reduces traffic in some parts of the network // reduces
congestion
• … because traffic only travels through the parts necessary
• … which hides the complexity of network
• … and allows for easier maintenance of the network
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On this page, free: the mark scheme for AS & A Level Computer Science 9618/13, October/November 2024 (9618_w24_ms_13), and the question paper (9618_w24_qp_13), to read or download, with each question's marking points written out underneath.
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Computer Science 9618/13 for October/November 2024 is out of 75 marks, with 1 hour 30 minutes to answer it.
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Yes. Upload your answers to 9618/13/O/N/24 as a PDF or photos, and CIE Buddy marks every question against this paper's official mark scheme, using Cambridge's marking rules. You get your score, each lost mark explained on your own script, and the topics to revise. It's a guide, not an official Cambridge grade.