IGCSE Past Papers — CS Compass

1 0478_m25_qp_12_Q1(a) 7 marks

1 (a) Complete the sentences about number systems.

Use the items from the list. Some of the items in the list will not be used. You should only use an item once.

A B C D E F G H W X Y Z 0 1 2 4 8 10 16 127 128 255 256

The binary number system is base ......................... . The smallest denary number that can be represented as an 8-bit binary number is ......................... . The largest denary number that can be represented as an 8-bit binary number is ......................... .

The hexadecimal number system is base ......................... . Each hexadecimal digit is equivalent to ......................... bits. The numbers 1 to 9 are used and the number 10 is represented by ......................... . The hexadecimal number system continues up to the number 15, which is represented by ......................... .

2 0478_m25_qp_12_Q1(b) 3 marks

1 (b) Two 8-bit binary numbers are given.

Add the two 8-bit binary numbers using binary addition.

Give your answer in binary. Show all your working.

   1 0 0 1 1 0 1 1
+  0 0 0 1 0 0 1 1

📋 Mark Scheme Answer

1 mark for correct working, 1 mark for each correct nibble.

   1 0 0 1 1 0 1 1
+  0 0 0 1 0 0 1 1
---------------
   1 0 1 0 1 1 1 0
          1   1 1

3 0478_m25_qp_12_Q1(c) 1 mark

1 (c) Binary addition can result in overflow.

Tick (✓) one box to show the correct definition of overflow in binary addition.

A The answer has created a negative number that cannot be represented in binary addition.

B The answer is the result of a logical shift that cannot be performed in binary addition.

C The answer is too large to represent in the number of bits available.

D The answer is too small to represent in the number of bits available.

4 0478_m25_qp_12_Q2(a) 1 mark

An artist creates an image on a computer.

2 (a) State what is meant by the colour depth of an image.

5 0478_m25_qp_12_Q2(b) 2 marks

2 (b) Describe the relationship between the resolution of the image and the file size of the image.

6 0478_m25_qp_12_Q2(c)(i) 3 marks

2 (c) The artist compresses the image file before uploading it to their website. Users can download the image file from the website to print as a poster.

The image file is compressed using lossless compression.

(i) Explain the reasons why the artist chose lossless compression instead of lossy compression to compress this image file.

7 0478_m25_qp_12_Q2(c)(ii) 3 marks

2 (c)(ii) Describe how lossless compression reduces the size of the image file.

8 0478_s25_qp_11_Q1(a) 1 mark

1 The size of a file can be measured using different data storage units.

(a) Tick (✓) one box to show the smallest data storage unit.

A byte
B gibibyte (GiB)
C kibibyte (KiB)
D nibble

9 0478_s25_qp_11_Q1(b) 1 mark

1 (b) State how many tebibytes (TiB) are equal to 2 pebibytes (PiB).

10 0478_s25_qp_11_Q1(c)(i) 1 mark

1 (c)(i) The size of a file needs to be reduced.

Give the name of the process that is used to reduce the size of a file.

11 0478_s25_qp_11_Q1(c)(ii) 1 mark

1 (c)(ii) One reason the size of a file may need reducing is so that it has a shorter transmission time.

Give one other reason why the size of a file may need reducing.

12 0478_s25_qp_11_Q2(a) 1 mark

A clothes store has a ticket system to allow customers to speak to a personal shopper. The ticket displays a ticket number in hexadecimal, for example 11B.

(a) The ticket system has an output device that creates a paper ticket.

Identify an appropriate output device to produce the paper ticket.

13 0478_s25_qp_11_Q2(b)(i) 2 marks

Each ticket number is stored as a binary number in the ticket machine.

2 (b)(i) Two ticket numbers are 14B and 97A.

Convert the two ticket numbers from hexadecimal to binary.

14B ..........................................................................

97A ..........................................................................

14 0478_s25_qp_11_Q2(b)(ii) 2 marks

2 (b)(ii) Give two reasons why the ticket number is displayed as hexadecimal instead of binary.

15 0478_s25_qp_11_Q2(c)(i) 2 marks

The ticket numbers could also be represented as denary.

2 (c)(i) Convert the two ticket numbers from hexadecimal to denary.

02C ..........................................................................

10B ..........................................................................

16 0478_s25_qp_11_Q2(c)(ii) 2 marks

2 (c)(ii) Convert the two denary numbers into hexadecimal.

109 ..........................................................................

415 ..........................................................................

17 0478_s25_qp_11_Q3 4 marks

3 An image is converted to binary to be represented by a computer.

Complete the table with the missing terms and definition about representing an image.

Term	Definition
pixel	....................................................
resolution	....................................................
....................................................	This is the number of bits used to create each colour in an image.
....................................................	This is additional data that is stored with an image that can provide information such as the time and date the image was taken.

Term	Definition
pixel	It is the smallest component of an image.
resolution	The number of pixels high by the number of pixels wide // The number of pixels in an image
colour depth // bit depth	This is the number of bits that are used to create each colour in an image.
metadata // header	This is additional data that is stored with an image that can provide information such as the time and date the image was taken.

18 0478_s25_qp_12_Q1(a) 1 mark

A computer stores data temporarily in random access memory (RAM).

(a) RAM is one example of primary storage.

Give one other example of primary storage.

[1]

19 0478_s25_qp_12_Q1(b) 1 mark

(b) Give one reason why data is only stored temporarily in the RAM.

[1]

20 0478_s25_qp_12_Q1(c) 2 marks

(c) The denary numbers 19 and 230 are converted to binary numbers to be stored in the RAM.

Convert the two denary numbers to binary numbers.

19

230

[2]

Working space

21 0478_s25_qp_12_Q1(d) 2 marks

(d) The hexadecimal numbers 35 and 8AD are converted to binary numbers to be stored in the RAM.

Convert the two hexadecimal numbers to binary numbers.

35

8AD

[2]

Working space

22 0478_s25_qp_12_Q1(e) 3 marks

(e) The 8-bit binary numbers 01100101 and 01110000 are stored in RAM.

The binary numbers are added together.

Add the two binary numbers using binary addition.

Give your answer in binary. You must show all your working.

  0 1 1 0 0 1 0 1
+
  0 1 1 1 0 0 0 0

[3]

📋 Mark Scheme Answer

1(e) One mark for each correct nibble (MAX 2). One mark for a correct method of working e.g. showing carries.

           1  1
0 1 1 0 0 1 0 1
+
0 1 1 1 0 0 0 0

           1 1 0 1 0 1 0 1

23 0478_s25_qp_12_Q1(f) 2 marks

(f) An overflow occurs when two other 8-bit binary numbers are added together.

Explain why the overflow error occurs.

[2]

24 0478_s25_qp_12_Q1(g) 2 marks

(g) The negative denary number –22 is stored in RAM.

Negative denary numbers can be represented as binary using two's complement.

Give the two's complement 8-bit binary integer that would be stored for the denary number –22.

You must show all your working.

Working space

Two's complement 8-bit binary integer

[2]

25 0478_s25_qp_12_Q2(a) 1 mark

A student has an image file stored on their computer.

(a) The image file was taken by a digital camera.

Tick (✓) one box to show whether a digital camera is an example of an input, output, process or storage device.

A	input
B	output
C	process
D	storage

[1]

26 0478_s25_qp_12_Q2(b)(i) 1 mark

(b) The size of the image file is 3072 bytes.

(i) Give the size of the image file in kibibytes (KiB).

[1]

27 0478_s25_qp_12_Q2(b)(ii) 1 mark

(ii) State the number of nibbles in 1 byte.

[1]

Working space

28 0478_s25_qp_12_Q2(c)(i) 1 mark

(c) The image file has a colour depth of 32 bits.

(i) State what is meant by a colour depth of 32 bits.

[1]

29 0478_s25_qp_12_Q2(c)(ii) 2 marks

(ii) The colour depth of the image file is changed to 64 bits.

Explain what effect this change has on the image file.

[2]

30 0478_s25_qp_12_Q2(d) 3 marks

(d) The student uses lossless compression to compress the image file.

Explain how the image file is compressed using lossless compression.

[3]

31 0478_s25_qp_13_Q1(a) 1 mark

1 A student records himself singing a song for his music project. The recorded sound is converted to binary to be processed by a computer.

(a) Give one input device the student can use to record the song.

[1]

32 0478_s25_qp_13_Q1(b) 1 mark

(b) The student uses sound editing software to edit the recorded sound.

Tick (✓) one box to show whether sound editing software is an example of application, security, system or utility software.

A application software
B security software
C system software
D utility software

[1]

33 0478_s25_qp_13_Q1(c)(i) 2 marks

(c) Two binary numbers stored from the recording are 00011001 and 10110100.

(i) Convert the two binary numbers to denary numbers.

00011001

10110100 [2]

34 0478_s25_qp_13_Q1(c)(ii) 2 marks

(ii) Convert the two binary numbers to hexadecimal numbers.

00011001

10110100 [2]

35 0478_s25_qp_13_Q1(c)(iii) 1 mark

(iii) A logical right shift of two places is performed on the binary number 10100100.

Give the binary number that would be stored after the logical shift has taken place.

[1]

36 0478_s25_qp_13_Q1(d) 2 marks

(d) The two's complement 8-bit binary integer 11001001 is also stored.

Convert the two's complement 8-bit binary integer to denary. Show all of your working.

Working space

Denary value [2]

37 0478_s25_qp_13_Q1(e) 3 marks

(e) The table contains terms and descriptions about the process of converting analogue sound to binary.

Complete the table with the missing term and descriptions.

Term	Description
	This is the measurement of the height (amplitude) of a sound wave taken at regular time intervals.
sample rate
sample resolution

[3]

Term	Description
(sound) sampling/sample	This is the measurement of the height (amplitude) of a sound wave at regular time intervals.
sample rate	The number of samples recorded each second
sample resolution	The number of bits that are used to record each sample

38 0478_w25_qp_11_Q1(a) 1 mark

A student has an electronic calculator. The calculator has a screen that displays the result of calculations.

The calculator has 8-bit registers.

(a) State the highest denary number that could be stored in a single 8-bit register.

39 0478_w25_qp_11_Q1(b) 2 marks

(b) Denary numbers are typed into the calculator. They are converted to binary numbers and stored in the 8-bit registers.

The student types in the denary number 23 and the denary number 168.

Give the 8-bit binary numbers that are stored in the registers for these two denary numbers.

23

168

40 0478_w25_qp_11_Q1(c) 1 mark

(c) The result of a calculation that is stored in a register is the binary number 00001011

Give the denary number that will be displayed on the screen for this binary number.

00001011

41 0478_w25_qp_11_Q1(d) 1 mark

(d) Another result of a calculation that is stored in a register is the binary number 01000010

Give the denary number that will be displayed on the screen for this binary number.

01000010

42 0478_w25_qp_11_Q1(e) 3 marks

(e) Two binary numbers stored in the registers are 01110110 and 00110000

Add the binary numbers using binary addition. Show all your working.

Give your answer in binary.

0 1 1 1 0 1 1 0

+

0 0 1 1 0 0 0 0

43 0478_w25_qp_11_Q1(f) 1 mark

(f) The result of a calculation could be a negative denary number.

State how the calculator could represent a negative denary number as a binary number.

44 0478_w25_qp_11_Q2(a) 2 marks

An employee of a company sells houses. He sends images of the houses to his company.

(a) The employee compresses the image files using lossy compression before sending them. Lossy compression reduces the size of the image files.

Give two other reductions that lossy compression makes to the images.

1 .........................................................................................................................................................................................................

2 .........................................................................................................................................................................................................

45 0478_w25_qp_11_Q3(a) 3 marks

A student has a portable device. He uses an on-screen keyboard to write messages to his friend.

(a) Explain how the text the student writes is converted to binary to be processed.

46 0478_w25_qp_12_Q1(a) 1 mark

A toy store gives each of the toys it sells a unique code. The codes are 3-digit hexadecimal codes, for example A4B.

A computer is used to store a database of the codes. The computer has 12-bit registers.

(a) Give the largest hexadecimal number that can be stored in a 12-bit register.

47 0478_w25_qp_12_Q1(b) 1 mark

(b) Give the largest denary number that can be stored in a 12-bit register.

48 0478_w25_qp_12_Q1(c) 2 marks

(c) Two toys have the hexadecimal codes 429 and 1A3.

Convert the two hexadecimal codes to 12-bit binary numbers.

429 ..........................................................................................................................................................................................................................................................................

1A3 .........................................................................................................................................................................................................................................................................

49 0478_w25_qp_12_Q1(d) 2 marks

(d) Two binary numbers that are stored in the registers are 100010100001 and 011100001011.

Convert the two binary numbers to hexadecimal numbers.

100010100001 ..............................................................................................................................................................................................................

011100001011 ..............................................................................................................................................................................................................

50 0478_w25_qp_12_Q2(a) 4 marks

2 Two binary numbers are stored in a computer.

(a) Add the two binary numbers using binary addition.

Give your answer in binary. Show all of your working.

   11110101
+  00111001

📋 Mark Scheme Answer

One mark for each correct nibble (2). One mark for a correct method of working for example 4 or 5 correct carries. One mark for showing an overflow error.

 (1) 111      1

   11110101
+  00111001
--------------
1  0010 1110

Result: 0010 1110 with overflow (1)

51 0478_w25_qp_12_Q2(b) 3 marks

(b) A logic right shift of three places is performed on the binary number 11110101.

Give the denary number for the binary number that would be stored after the logical shift of three places has occurred. Show all of your working.

52 0478_w25_qp_13_Q1(b)(i) 1 mark

(b) The owner of the shop enters a denary number to set the temperature for the room.

The denary number is converted to a binary number to be processed. The binary number is stored in a register in the air conditioning system.

(i) Give the binary number that would be stored when the denary number 24 is entered.

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

53 0478_w25_qp_13_Q1(b)(ii) 1 mark

(ii) Give the binary number that would be stored when the denary number 101 is entered.

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

54 0478_w25_qp_13_Q1(b)(iii) 1 mark

(iii) The binary number 00010011 is stored in the register.

Give the denary number that has been entered for this binary number to be stored.

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

55 0478_w25_qp_13_Q1(b)(iv) 1 mark

(iv) The binary number 00100010 is stored in the register.

Give the denary number that has been entered for this binary number to be stored.

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

56 0478_w25_qp_13_Q1(c)(i) 1 mark

(c) If the air-conditioning system detects an error, it displays an error code. The error code is displayed as a hexadecimal number. The binary number for each error code is stored in a register.

(i) Give the binary number that is stored in the register to display the error code 51.

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

57 0478_w25_qp_13_Q1(c)(ii) 1 mark

(ii) Give the binary number that is stored in the register to display the error code E3.

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

58 0478_w25_qp_13_Q1(c)(iii) 1 mark

(iii) Give the hexadecimal number that is displayed when the binary number 10000010 is stored in the register.

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

59 0478_w25_qp_13_Q1(d) 2 marks

(d) If the owner of the shop wants to make the room very cold, she may need to enter a negative denary number.

The negative denary number could be represented using two's complement.

Give the two's complement 8-bit binary integer that would be stored for the temperature –5.

Show all your working.

Working space ..............................................................................................................................................................................................

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

Two's complement 8-bit binary integer ...............................................................................................................................

[2]

60 0478_w25_qp_13_Q5(a) 5 marks

Text, images and sound are represented as binary to be processed by a computer.

(a) Complete the table by writing the missing terms and descriptions about representing text, images and sound as binary.

Term	Description
character set
	This is the number of samples taken each second when recording sound.
pixel
resolution
	This is the number of bits used to represent a colour in an image.

[5]

Term	Description
character set	This stores all the characters and their unique binary values.
sample rate	This is the number of samples taken each second when recording sound.
pixel	This is the smallest unit / part of an image.
resolution	This is the number of pixels that appear in an image / displayed on a screen // The number of pixels high by the number of pixels wide.
colour depth // bit depth	This is the number of bits used to represent a colour in an image.

61 0478_w25_qp_13_Q5(b) 1 mark

(b) The size of an image file is 1000 bytes.

Give the size of the image file in bits.

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

62 0478_w25_qp_13_Q5(c) 1 mark

(c) The size of a sound file is 4096 mebibytes (MiB).

Give the size of the file in gibibytes (GiB).

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

1 Data Representation · 62 Q