A Level Computer Science Paper 1 2025 OctNov

A Level Computer Science Paper 1 2025 Oct/Nov

1011 0011 1010
1011 0011 1010
11 = B 3 10 = A

B3A

1 0 8
0001 0000 1000
000100001000

000100001000

111110111100
-68
Since the MSB is 1, the number is negative.
Invert all the bits: 1 1 1 1 1 0 1 1 1 1 0 0 0 0 0 0 0 1 0 0 0 0 1 1
Add 1 to the result: 000001000011 + 1 = 000001000100
This is one’s complement!
This is two’s complement!
Convert this number to denary: 000001000100 = 64 + 4 = 68
Apply the negative sign to 68:

1. Invert the bits = 000001000011
2.Add 1 to result = 000001000100
3.Convert to denary = 64+4 = 68
4.Apply negative sign = -68
-68

1 0 1 1 0 0 1 1
Answer is: 00101011 (with an extra carry bit of 1)
The complete 9-bit mathematical result is 1 00101011. Since it
must fit into an 8-bit register, the final stored value becomes
00101011.
0 1 1 1 0
0
0
1
+
1
1
0
1
0
1
0
0
(1)
1
1
1
0+0=0
0+1 = 1
1 +0= 1
1 +1 = 10
1 + 1 + 1 = 11
Helping Box

(ii) Name and describe the error that can occur when
binary addition is performed.
Name: Overflow error
Description:
This occurs when the result of an addition is too large to fit
within the allocated number of bits (in this case, 8 bits).
It causes the most significant carry bit to be discarded,
leading to an incorrect or mathematically invalid final value.

1
1
0
1
0
1
0
0
(1)
Name: Overflow error
Description: This occurs when the result of an addition is too large to fit within
the allocated number of bits (in this case, 8 bits). It causes the most significant
carry bit to be discarded, leading to an incorrect value.

Draw a line between STUDENT and
PLACEMENT with a "crow's foot" (three-
pronged end) at the PLACEMENT side.
Draw a line between COMPANY and
PLACEMENT with a "crow's foot" at
the PLACEMENT side.
STUDENT to PLACEMENT:
A One-to-Many (1:M) relationship.
One student can have multiple
placements, but each placement
belongs to only one student.
COMPANY to PLACEMENT:
A One-to-Many (1:M) relationship.
One company can host many
placements, but each placement is
associated with only one company.
Helping Box
First Normal Form (1NF): All
attributes are atomic (no repeating
groups), and each record is unique via
a primary key.
Second Normal Form (2NF): It is in
1NF and every non-key attribute is
fully functionally dependent on the
primary key (there are no partial
dependencies).
Third Normal Form (3NF): It is in
2NF and there are no transitive
dependencies. This means every
non-key attribute depends only
on the primary key and not on
any other non-key attributes.
It satisfies the first and second normal form (1NF & 2 NF) because all attributes
are atomic and there are no partial dependencies. It also satisfies 3NF as there
are also no transitive dependencies. Every non-key attribute only depends on the
primary key only, not other non-key attributes.

DELETE FROM PLACEMENT
WHERE Complete = TRUE;
use the COUNT
function with a
WHERE clause
SELECT COUNT(*) AS TotalCompleted
FROM PLACEMENT
WHERE StudentID = 'LDEA01'
AND CompanyID = 'NEAM'
AND Complete = TRUE;

Referential integrity ensures that relationships between tables remain consistent. Any foreign key
must have a corresponding valid primary key value in the related table.
Application to this database: It applies in two areas:
Student Link: The StudentID in the PLACEMENT table is a foreign key. Referential integrity ensures
that you cannot add a placement for a StudentID that does not exist in the STUDENT table.
Company Link: CompanyID in the PLACEMENT table must match an existing CompanyID in the
COMPANY table.

A NAND B
NOT A
NOT C
NOT A AND NOT C
(A NAND B)
XOR
(NOT A OR NOT C)
NOT
(A NAND B)
XOR
(NOT A OR NOT C)

We look at the rows
where the output Q = 1
Row 2
Row 7
Minterm for row 2
R = 0, S = 0, T = 1
NOT R AND NOT S AND T
Minterm for row 7
R = 1, S = 1, T = 0
R AND S AND NOT T
(NOT R AND NOT S AND T) OR (R AND S AND NOT T)

LSL #2
Shifting bits 2 places to the left

ACC XOR &12 means we perform a bitwise XOR operation
between the current ACC value and the hexadecimal value &12
In assembly language, the & (or sometimes #&) prefix denotes a
hexadecimal value.
& 1 2 in hex means 00010010 in binary
Take XOR of ACC and this binary number

1 1 1 0 0 0 1 1
0 0 0 1 0 0 1 0
+
The XOR Rule:
Write 1 if bits are different
Write 0 if bits are same
__________________
1
0
0
0
1
1
1
1

1
0
0
0
1
1
1
1

AND #63 means we perform a bitwise AND operation between the
current ACC value and the binary representation of decimal 63.
# 6 3 in denary means 00111111 in binary
Take AND of ACC and this binary number

1 1 1 0 0 0 1 1
0 0 1 1 1 1 1 1
The AND Rule:
Write 1 only if BOTH bits
are 1 otherwise 0
__________________
1
1
0
0
0
1
0
0
A N D

1
1
0
0
0
1
0
0

ACC OR 100 means we perform a bitwise OR operation between the
current ACC value and the data stored at memory address 100.
Data value at address 100 is 00110011
Take OR of ACC and this binary number

1 1 1 0 0 0 1 1
0 0 1 1 0 0 1 1
The OR Rule:
Write 1 only if atleast 1 bit is 1
write 0 if both bits are 0
__________________
1
1
0
0
1
1
1
1
O R

1
1
0
0
1
1
1
1

Processor Management: Allocating CPU time to different processes and
scheduling tasks to ensure efficient execution.
Memory Management: Tracking and allocating RAM to various programs and
ensuring they do not interfere with each other's memory space.
User Authentication: Managing usernames and passwords (or biometric data)
to ensure only authorized users can access the system.
Access Control: Setting file permissions and privileges to prevent
unauthorized users from reading, modifying, or deleting sensitive data.

One major benefit is reduced development time. Since library routines are
pre-written and pre-tested, developers do not need to write the code from
scratch which leads to faster completion and higher reliability as routines
are already debugged.
A significant drawback is a lack of control and complexity. Because routine is
written by a third party, developer cannot easily modify the internal code.
The final executable file size may increase (bloat) because the library might
include extra code that isn’t actually needed for the specific project.

Syntax Highlighting: Uses different colors to distinguish between keywords, variables, and
operators, making code easier to read and debug.
Code Indentation/Formatting: Automatically aligns blocks of code (like loops or functions)
to visually represent the structure and hierarchy of the program.

Stores the results of calculations and logical operations
performed by the Arithmetic Logic Unit (ALU).
Holds the instruction that is currently being decoded
and executed.

Software Compatibility: Not all software is designed to use multiple cores (parallel
processing). If a program is written for a single core, it won't run faster on a multi-
core processor.
Overhead and Communication: Coordinating tasks between many cores requires
complex management, which can lead to "overhead" that slows down the system.
Power and Heat: More cores generally consume more power and generate more
heat, requiring better cooling systems and reducing battery life in portable devices.

Speed: DRAM has slower access speed and SRAM has faster access speed.
Refreshing: DRAM needs to be constantly refreshed thousands of times per second.
SRAM does not need refreshing as long as power is supplied.
Cost/Capacity: DRAM is cheaper to produce and has high density (more storage in
less space) but SRAM is more expensive and taes up more physical space (less
density)
Typical Use: Main memory (System RAM) is a DRAM and Cache memory (L1, L2, L3
cache) is SRAM

An IP address that is permanently assigned to a device
and does not change over time or each time the device
connects to the network.
An IP address assigned by an ISP that is visible to the
entire internet, allowing a device to be identified and
communicate with external networks.

An IPv4 address must consist of four decimal numbers (octets) separated by dots,
where each number ranges from 0 to 255. This address is invalid because:
Out of range: The first octet (256) exceeds the maximum allowable value of 255.
Invalid character: The fourth octet (A) is a letter; IPv4 addresses only use numeric
digits.

DNS Lookup: The browser sends the domain name part of the URL (e.g., example.com) to a
Domain Name System (DNS) server. The DNS server looks up and returns the
corresponding IP address of the web server.
Establish Connection: Using the IP address, the browser establishes a connection with the
web server, typically using the TCP/IP protocol.
HTTP Request: The browser sends an HTTP (or HTTPS) request to the web server to fetch
the specific resources (like HTML, CSS, and images) indicated by the rest of the URL path.
Server Response: The web server processes the request and sends back the requested
data in an HTTP response.
Rendering: The web browser receives the data (HTML code) and renders it into the visual
web page that the user sees on their screen.

A maximum of 256 colors means the image uses 8 bits per pixel. 2
8
= 256
Total bits = Bits per pixel x Width x Height = 8 x 512 x 2048 = 8,388,608 bits
Convert to Kibibytes (KiB) = 8,388,608 ÷ 8 ÷ 1024 = 1024 KiB
1024

The actual file size is often larger than the calculated size because the
calculation (1024 KiB) usually only accounts for the raw data (like pixels or
audio samples).
Two common reasons for this are:
Metadata: Files include extra information such as the file name, date created,
dimensions, or author details.
File Headers: Every file format (e.g., .jpg, .mp3) requires a header at the
beginning of the file to tell the computer how to read and process the data.

Run-length encoding (RLE) is a lossless compression method that reduces the size
of a bitmap by identifying sequences of identical pixels.
Identifying Runs: The algorithm scans the image (usually row by row) to find runs,
which are consecutive pixels of the same color.
Storing Pairs: Instead of storing every individual pixel, it stores each run as a data
pair: the number of pixels (the run length) followed by the color code (the pixel
value).
Example
A row of 10 white pixels would be stored as 10, White rather than listing the code
for "White" ten separate times. This significantly reduces file size for images with
large areas of solid color.

A piece of malicious code that replicates itself by attaching to other
programs or files. It is designed to spread from one computer to another,
often damaging data or corrupting the system.
A cyberattack that redirects a user from a legitimate website to a
fake, malicious one without their knowledge. This is typically achieved by
infecting the computer or server to change DNS settings, often to steal
personal information like login credentials.

Security and Malware: Ensuring the personal device is free from viruses or
malware that could spread and compromise the integrity of the school's
network.
Appropriate Use: Adhering to the school’s Acceptable Use Policy (AUP) by
not accessing illegal, harmful, or inappropriate content while connected to
the institution's infrastructure.
Data Privacy and Confidentiality: Respecting the privacy of others by not
attempting to access, intercept, or share unauthorized data belonging to
other students or the school.

Decline in Critical Thinking and Problem-Solving Skills
If students rely heavily on AI to generate answers, they may fail to develop the essential
cognitive skills required to analyze information independently. This can lead to a long-
term social issue where future professionals lack the deep understanding and original
thought necessary for complex decision-making.
Increased Digital Divide and Inequality
Students with better access to advanced, paid AI tools may achieve higher grades or
complete work more efficiently than those without such resources. This can widen the
educational gap between different socioeconomic groups, creating an unfair advantage
based on financial status rather than merit.

Feature Monitoring System Control System
Primary Function
Observes and records data from the
environment.
Observes data and takes action to manage
the environment.
Output/Action
Provides a report, alert, or warning (e.g.,
an alarm sounds) but does not change
the state of the system.
Sends signals to actuators to change the
system's state (e.g., turning a heater
on/off).
Feedback Loop
Open-ended: It tells a human something
is wrong, and the human must intervene.
Closed-loop: It automatically adjusts the
process to maintain a set point without
human intervention.
Example:
A monitoring system only observes and warns of changes (e.g., a hospital vital signs monitor), whereas a control system
actively adjusts the process to reach or maintain a specific target (e.g., a thermostat maintaining room temperature).

Digital Design: First, a Computer-Aided Design (CAD) model of the building is created.
This digital file is then converted into a format the printer understands (like an STL file)
and "sliced" into many thin horizontal layers.
Layer-by-Layer Construction: The printer reads the design and deposits material (such
as plastic filament or resin) layer by layer from the bottom up.
Solidification: Each layer is fused to the previous one—often by melting the material
through a heated nozzle or using a laser to cure resin—until the final 3D object is
complete.

A 3D printer needs a buffer to compensate for the difference in speed
between the computer sending the data and the printer
processing/executing the print commands.
This ensures that the printer can operate continuously without pauses
while waiting for the next set of instructions.

A Level Computer Science Paper 1 2025 OctNov

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