Computer Science — A-Level

Practice Paper 1 (Cambridge International A-Level Computer Science)

16 questions · 65 marks · ≈ 65 min · spans 16 of 45 topics

Assembled from the topic question banks — not an official Cambridge International paper

Guided practice

15 markshard

One row of a bitmap photograph has a colour depth of 8 bits per pixel. The colour of each pixel is written as a two-digit hexadecimal value:

1C 4E 90 22 FD 07 B3 6A

The photograph is compressed using run-length encoding (RLE). Each RLE pair is written as the number of repeats followed by the colour value. In the compressed file, the count and the colour value are each stored in one byte.

(i) Write the RLE compressed data for this row.

(1 mark)

(ii) Calculate the size of this row in bytes before compression and after compression.

(2 marks)

(iii) Explain why run-length encoding is not appropriate for this row.

(2 marks)

Your answer

How did you do?/ 5

24 markshard

A 12-bit register holds the bit pattern 0110 1011 0010.

A student says that this is a Binary Coded Decimal (BCD) value.

(a) Explain why the student is wrong.

(b) State the largest denary value that this 12-bit register can hold using BCD, and the largest denary value it can hold using unsigned binary.

Your answer

How did you do?/ 4

34 markshard

A wildlife camera saves each photograph as an uncompressed bitmap file.

Each file contains:

pixel data for an image with an image resolution of 1024 pixels wide by 1024 pixels high
a colour depth of 8 bits per pixel
a file header of 1024 bytes

(i) Calculate the total size of one file, including the file header. Give your answer in kibibytes.

Show your working.

(2 marks)

(ii) The camera has 20 mebibytes of storage available for photographs.

Calculate the largest number of complete files the camera can store.

Show your working.

(2 marks)

Your answer

How did you do?/ 4

46 marksmedium

(a)

A company sells online Computer Science courses to students in different countries. The courses are stored on a public cloud.

(i) Explain why the company uses a public cloud to store these courses.

(2 marks)

(ii) Describe two disadvantages of storing data on a public cloud compared to storing data on a server in a Local Area Network (LAN).

(4 marks)

Your answer

How did you do?/ 6

55 markshard

An office uses a laser printer to print documents.

Describe the principal operations of the laser printer, from the point at which the print data reaches the printer to the point at which the printed page leaves the printer.

Your answer

How did you do?/ 5

64 markshard

The truth table has one output column for each of three two-input logic gates.

Complete the truth table.

A	B	A AND B	A XOR B	A NAND B
0	0
0	1
1	0
1	1

Use your completed table to state which one of these three gates gives an output of 1 for the greatest number of input combinations. Give that number.

Your answer

How did you do?/ 4

73 marksmedium

The table shows part of the instruction set for a processor. The processor has two registers, the Accumulator (ACC) and the Index Register (IX).

Opcode	Operand	Explanation
`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 the given 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
`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, for example #123.

The current contents of memory are shown.

Address	Data
70	74
71	6
72	19
73	71
74	33
75	8
76	41

The current contents of the ACC and the IX are shown.

Register	Content
ACC	5
IX	3

The ACC and the IX are reset to these values before each set of instructions is run.

Complete the table by writing the content of the ACC and the content of the IX after each set of instructions has run.

Set number	Instructions	ACC content	IX content
1	`LDR #2` `LDX 73`
2	`LDI 73`
3	`LDD 72` `DEC ACC`

Your answer

How did you do?/ 3

83 marksmedium

(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
`AND`	`<address>`	Bitwise AND operation of the contents of ACC with the contents of
`XOR`	`#n/Bn/&n`	Bitwise XOR operation of the contents of ACC with the operand
`XOR`	`<address>`	Bitwise XOR operation of the contents of ACC with the contents of
`OR`	`#n/Bn/&n`	Bitwise OR operation of the contents of ACC with the operand
`OR`	`<address>`	Bitwise OR operation of the contents of ACC with the contents of
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.

Your answer

How did you do?/ 3

92 markseasy

A processor contains a system clock.

(i) State what is meant by the clock speed of a processor.

(1 mark)

(ii) State the unit in which clock speed is measured.

(1 mark)

Your answer

How did you do?/ 2

102 markseasy

A programmer writes a program in a high-level language using an Integrated Development Environment (IDE).

The IDE provides features for initial error detection.

Describe how a dynamic syntax check helps the programmer.

Your answer

How did you do?/ 2

117 marksmedium

4 marks

(a)

A student uses a laptop to write a program that is saved as a text file.

The laptop has utility software and an Operating System (OS).

(i) Describe the file management tasks carried out by an OS.

(2 marks)

(ii) Explain the need for back-up software.

(2 marks)

Your answer

3 marks

(c)

The student used a program library when writing their program.

Explain the benefits to the student of using library files when writing a program.

Your answer

How did you do?/ 7

124 marksmedium

(c)

A class of students are developing a program to send data between computers. Many computers are connected together to form a wired network. Serial ports are used to connect one computer to another.

Each computer:

is assigned a unique three-digit ID
has three ports, each identified by an integer value
is connected to between one and three other computers.

Messages are sent between computers as a string of characters organised into fields as shown:

<STX><DestinationID><SourceID><Data><ETX>

Field number	Field name	Description
n/a	`STX`	a single character marking the start of the message (ASCII value 02)
1	`DestinationID`	three numeric characters that identify the destination computer
2	`SourceID`	three numeric characters that identify the source computer
3	`Data`	a variable length string containing the data being sent (Minimum length is 1 character)
n/a	`ETX`	a single character marking the end of the message (ASCII value 03)

For example, the following message contains the data "Hello Kevin" being sent from computer "101" to computer "232":

<STX>"232101Hello Kevin"<ETX>

Each computer will run a copy of the same program. Each program will contain a global variable, MyID of type string, that contains the unique ID of the computer in which the program is running.

The programmer has defined the first two program modules as follows:

Module	Description
`Transmit()` (already written)	- takes two parameters: - a string containing a message - an integer containing a port number - transmits the message using the given port
`SendFile()`	- takes three parameters: - a string containing a text file name - a string containing a Destination ID - an integer containing a Port number - transmits the file one line at a time - transmits a final message with data string "**"

One of the text files to be sent contains several blank lines (lines that do not contain any text).

(i) Explain why this is a problem.

(2 marks)

(ii) Explain how the message format could be changed to allow a blank line to be sent.

(2 marks)

Your answer

How did you do?/ 4

133 marksmedium

A company sells online Computer Science courses to students in different countries.

The courses are stored on a public cloud.

State how the following security measures can be used to protect computer systems.

Firewall ...............................................

Encryption ..........................................

Passwords ..........................................

Your answer

How did you do?/ 3

142 markseasy

A hospital uses an Artificial Intelligence (AI) system to help its doctors identify illnesses from medical images.

Give two social impacts of using this system.

Your answer

How did you do?/ 2

155 marksmedium

The company has another database, FARMING, for a different game.

The database FARMING has a table named EVENT which is shown with some sample data.

PlayerID	EventID	Category	Points
`000123`	`3`	`Build`	`100`
`000124`	`1`	`Grow`	`36`
`000123`	`4`	`Grow`	`22`
`000123`	`7`	`Create`	`158`
`000125`	`3`	`Grow`	`85`
`000125`	`4`	`Build`	`69`

(i) The database FARMING has a second table created named PLAYER that has the primary key PlayerID.

The field PlayerID in EVENT needs to be set up as a foreign key to link to PlayerID in PLAYER.

Write a Structured Query Language (SQL) script to change the table definition for EVENT to link the foreign key to PLAYER.

(2 marks)

(ii) Write an SQL script to return the number of events that each player has completed.

(3 marks)

Your answer

How did you do?/ 5

166 marksmedium

1 mark

(a)

A theatre wants to use a database to store data about the shows that are scheduled, their customers and the seats that the customers have booked.

In the theatre:

Each show can take place on multiple dates.
Some dates can have more than one performance.
There are multiple rows of seats.
Each seat can be individually booked by its row letter and seat number, for example row E seat 2.

Part of the database design includes these tables:

SHOW(ShowID, Title, Duration)

SEAT(SeatID, RowLetter, SeatNumber)

PERFORMANCE(PerformanceID, ShowID, ShowDate, StartTime)

Identify the relationship between the tables PERFORMANCE and SHOW.

Your answer

5 marks

(d)

Customers give their first name, last name and email address when they are making a booking. One booking can include multiple seats.

Describe the additional tables that will need to be included in the database and explain how these tables will be linked within the database.

Your answer

How did you do?/ 6

A AND B

A XOR B

A NAND B

Opcode

Operand

Explanation

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 the given 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

DEC

register

Subtract 1 from the contents of the register (ACC or IX)

Address

Data

Content

ACC

Set number

Instructions

ACC content

IX content

LDR #2
LDX 73

LDI 73

LDD 72
DEC ACC

Instruction

Explanation

Opcode

Operand

AND

#n/Bn/&n

Bitwise AND operation of the contents of ACC with the operand

AND

<address>

Bitwise AND operation of the contents of ACC with the contents of

XOR

#n/Bn/&n

Bitwise XOR operation of the contents of ACC with the operand

XOR

<address>

Bitwise XOR operation of the contents of ACC with the contents of

OR

#n/Bn/&n

Bitwise OR operation of the contents of ACC with the operand

OR

<address>

Bitwise OR operation of the contents of ACC with the contents of

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

Field number

Field name

Description

n/a

STX

a single character marking the start of the message (ASCII value 02)

DestinationID

three numeric characters that identify the destination computer

SourceID

three numeric characters that identify the source computer

Data

a variable length string containing the data being sent (Minimum length is 1 character)

n/a

ETX

a single character marking the end of the message (ASCII value 03)

Module

Description

Transmit()
(already written)

- takes two parameters:

- a string containing a message
- an integer containing a port number
- transmits the message using the given port

SendFile()

- takes three parameters:

- a string containing a text file name
- a string containing a Destination ID
- an integer containing a Port number
- transmits the file one line at a time
- transmits a final message with data string "**"

PlayerID

EventID

Category

Points

000123

3

Build

100

000124

1

Grow

36

000123

4

Grow

22

000123

7

Create

158

000125

3

Grow

85

000125

4

Build

69