IGCSE COMPUTER SCIENCE PRACTICE
EXAM QUESTIONS AND ANSWERS
Explain why binary is used to store data in a computer system. - Answer-Computer
consist of transistors / logic circuits
... that can only store/process data in two states / as high-low / on-off / 1 and 0
Convert 1001 1011 to denary - Answer-128+16+8+2+1= 155
Convert 85 to binary - Answer-1010101
How many bits is in nibble and byte? - Answer-1nibble=4 bits
1 byte=8 bits
How many bytes in a kilobyte? - Answer-1024 bytes
Explain the differences between the binary system and the denary sytem. - Answer--
The Binary number system is base 2
-The Denary number system is base 10
-The Binary number system uses 0 and 1 values
-The Denary number system uses values from 0 to 9
-The Binary number system has units / placeholders / column headings that increase by
the power of 2
-The Denary number system has units / placeholders / column headings that increase
by the power of 10
-Binary has more digits for the same value OR Denary has fewer digits for the same
value
What is hexadecimal? - Answer-Base 16 number system
Convert the hexadecimal number B5 into binary. - Answer-1011 0101
Convert the binary number 1111 0110 into hexadecimal. - Answer-F6
What is the advantage of using hexadecimal numbers? - Answer--They are easier to
read and understands
-They make it easier to spot mistakes
-They are shorter / More can fit on the screen / 16 bits can be represented by 4 hex
digits
-It is easy to convert between Hex and Binary.
-Faster than binary for entering numbers
What is a MAC address? - Answer-A Media Access Control (MAC) address is a number
that uniquely identifies a device on the internet.
,--> (first part manufacturer ID) (second part serial number)
For example 23-45-97-89-AB-CD
first 6/8 digits = manufacturer code/ID of device (NIC)
last 6/8 digits = serial number of device (NIC)
It is a static address - It does not change
How hexadecimal is used to display ASCII/Unicode values? - Answer-Everytime you
type something on your keyboard for example "A" it will store the ascii value of 65.
Use of hexadecimal in HTML/CSS colour code. - Answer-The 6 digit hex colour code
should be considered in three parts.
First two digits represents the amount of red in the colour (max FF, or 255)
The next two digits represent the amount of green in the colour (max FF, or 255)
The final two digits represent the amount of blue in the colour (max FF, or 255)
E.g. orange can be represented as #FFA500, which is (255 red, 165 green, 0 blue).
Give an example of file format. - Answer-Sound - .mp3 .wav
Text- .txt .pdf
Picture- .jpeg .png .gif
Video- .mp4
What is a MIDI file? - Answer-Musical Instrument Digital Interface (MIDI) s contain a list
of commands that instruct a device how to produce a particular sound or musical note.
(set of commands instruction how the song should be played)
*MIDI files stored the notes played and not the sound.
e.g.
Durations of note
The volume of the note
Tempo
Type of instrument
Pitch of the note
Modulations
What are 2 types of file compression? - Answer-Lossy and Lossless
What is lossy compression? - Answer-Compression in which some of the information is
permanently eliminated
What is lossless compression? - Answer-Making the size of a file smaller without losing
any of the information in the file.
,How image file like jpeg reduce the file size? - Answer-JPEG is an image file that used
lossy compression to reduce the size of the file. It reduces the range of colour
used/colour depth/bits per pixel and reduces the number of pixels / removes
unnecessary data.
How mp3 reduce the file size? - Answer-The mp3 file should use a lossy compressed
file. It compresses by discarding any unnecessary sounds and sounds that humans
can't hear by reducing the rate of the amplitude of the sounds.
How mp4 reduce the file size? - Answer-The mp4 file is suitable to use lossy
compressed files.
− A compression algorithm is used
− The resolution could be reduced
− Colour depth could be reduced // bits per pixel reduced
− Sounds not heard by human ear could be removed // Perceptual music shaping can
be used
− Repeating frames could be removed
Describe how lossless compression reduces the file size of the video. (3 marks) -
Answer-− Compression algorithm used
− ..., e.g. RLE
− Repeating frames/pixels are identified
− ... and are collated/indexed
− No data is permanently removed
− It just records the changes between frames/pixels
How text file reduce the file size? - Answer-The text file is suitable to use as a lossless
compressed file because if you remove any word it can have an impact.
A compression algorithm is used to find and index repeated words or patterns (or
sections of words) within the data. The indexed words/patterns are then replaced with
numerical values. The index will need to be stored with the data to allow decompression
with no loss of data.
What is the advantage of using lossy compression over lossless compression in photo
images? - Answer--Lossy will reduce the file size more than lossless
-The redundant data can be removed from the files
-Images can still be of similar quality
-There is no requirement for the files to be exactly the same as the original
-Photos can be sent quicker / faster to upload / faster to download
What is the advantage of using lossless compression over lossy compression in photo
images and video? - Answer--Maintains quality // quality better than lossy
− Original file is retained // Data is not permanently lost − A significant reduction in file
size is not required
, The file Michele is sending contains the source code for a large computer program.
Identify which type of compression would be most suitable for Michele to use and
explain why? - Answer-Lossless because the file can be restored/decompressed to the
exact same state it was before compression and because it contains a text, with the use
of lossy compression it can ruin and remove the code and cannot run the code properly.
What are the 2 methods of transmission? - Answer-Serial transmission - sends data one
bit at a time over a single channel. (use a single wire)
Parallel data transmission - when several bits are sent at a time over multiple channels.
What are the 3 directions of transmission? - Answer-Simplex transmission - allows for
data to be sent in only one direction.(unidirectional)(serial)
e.g. a microphone
Half-duplex transmission - allows data to travel in both directions but cannot occur
simultaneously (only one direction at a time) // asynchronous (cannot occur at the same
time) (serial)
e.g. two-way radio (walkie talkie)
Full Duplex - allows data to travel in both directions simultaneously(at the same time)
(parallel)
e.g. telephone
Give an example of method for errors checking? - Answer-1.Parity check
2. Checksums
3.ARQ (Automatic Repeat reQuest)
4.Check digit
5.Echo check
How parity check detect the error? - Answer-The user will clarify if the parity bytes are
going to be even/odd. All the parity bytes have to be added to be either odd or even
depend on what parity set e.g. the user had used even parity 110110100 = 1+1+1+1+1
=5
--> Error founded
If parity bit is incorrect an error is detected like as shown in the example.
Why parity check do not always detect errors? - Answer-If an even number of bits are
changed during transmission (2,4,6,8) then the Parity check is not be able to detect the
error)
A system used odd parity. Complete these following two bytes of data so they both have
odd parity:
_1111000
_0000111 - Answer-11111000
00000111
EXAM QUESTIONS AND ANSWERS
Explain why binary is used to store data in a computer system. - Answer-Computer
consist of transistors / logic circuits
... that can only store/process data in two states / as high-low / on-off / 1 and 0
Convert 1001 1011 to denary - Answer-128+16+8+2+1= 155
Convert 85 to binary - Answer-1010101
How many bits is in nibble and byte? - Answer-1nibble=4 bits
1 byte=8 bits
How many bytes in a kilobyte? - Answer-1024 bytes
Explain the differences between the binary system and the denary sytem. - Answer--
The Binary number system is base 2
-The Denary number system is base 10
-The Binary number system uses 0 and 1 values
-The Denary number system uses values from 0 to 9
-The Binary number system has units / placeholders / column headings that increase by
the power of 2
-The Denary number system has units / placeholders / column headings that increase
by the power of 10
-Binary has more digits for the same value OR Denary has fewer digits for the same
value
What is hexadecimal? - Answer-Base 16 number system
Convert the hexadecimal number B5 into binary. - Answer-1011 0101
Convert the binary number 1111 0110 into hexadecimal. - Answer-F6
What is the advantage of using hexadecimal numbers? - Answer--They are easier to
read and understands
-They make it easier to spot mistakes
-They are shorter / More can fit on the screen / 16 bits can be represented by 4 hex
digits
-It is easy to convert between Hex and Binary.
-Faster than binary for entering numbers
What is a MAC address? - Answer-A Media Access Control (MAC) address is a number
that uniquely identifies a device on the internet.
,--> (first part manufacturer ID) (second part serial number)
For example 23-45-97-89-AB-CD
first 6/8 digits = manufacturer code/ID of device (NIC)
last 6/8 digits = serial number of device (NIC)
It is a static address - It does not change
How hexadecimal is used to display ASCII/Unicode values? - Answer-Everytime you
type something on your keyboard for example "A" it will store the ascii value of 65.
Use of hexadecimal in HTML/CSS colour code. - Answer-The 6 digit hex colour code
should be considered in three parts.
First two digits represents the amount of red in the colour (max FF, or 255)
The next two digits represent the amount of green in the colour (max FF, or 255)
The final two digits represent the amount of blue in the colour (max FF, or 255)
E.g. orange can be represented as #FFA500, which is (255 red, 165 green, 0 blue).
Give an example of file format. - Answer-Sound - .mp3 .wav
Text- .txt .pdf
Picture- .jpeg .png .gif
Video- .mp4
What is a MIDI file? - Answer-Musical Instrument Digital Interface (MIDI) s contain a list
of commands that instruct a device how to produce a particular sound or musical note.
(set of commands instruction how the song should be played)
*MIDI files stored the notes played and not the sound.
e.g.
Durations of note
The volume of the note
Tempo
Type of instrument
Pitch of the note
Modulations
What are 2 types of file compression? - Answer-Lossy and Lossless
What is lossy compression? - Answer-Compression in which some of the information is
permanently eliminated
What is lossless compression? - Answer-Making the size of a file smaller without losing
any of the information in the file.
,How image file like jpeg reduce the file size? - Answer-JPEG is an image file that used
lossy compression to reduce the size of the file. It reduces the range of colour
used/colour depth/bits per pixel and reduces the number of pixels / removes
unnecessary data.
How mp3 reduce the file size? - Answer-The mp3 file should use a lossy compressed
file. It compresses by discarding any unnecessary sounds and sounds that humans
can't hear by reducing the rate of the amplitude of the sounds.
How mp4 reduce the file size? - Answer-The mp4 file is suitable to use lossy
compressed files.
− A compression algorithm is used
− The resolution could be reduced
− Colour depth could be reduced // bits per pixel reduced
− Sounds not heard by human ear could be removed // Perceptual music shaping can
be used
− Repeating frames could be removed
Describe how lossless compression reduces the file size of the video. (3 marks) -
Answer-− Compression algorithm used
− ..., e.g. RLE
− Repeating frames/pixels are identified
− ... and are collated/indexed
− No data is permanently removed
− It just records the changes between frames/pixels
How text file reduce the file size? - Answer-The text file is suitable to use as a lossless
compressed file because if you remove any word it can have an impact.
A compression algorithm is used to find and index repeated words or patterns (or
sections of words) within the data. The indexed words/patterns are then replaced with
numerical values. The index will need to be stored with the data to allow decompression
with no loss of data.
What is the advantage of using lossy compression over lossless compression in photo
images? - Answer--Lossy will reduce the file size more than lossless
-The redundant data can be removed from the files
-Images can still be of similar quality
-There is no requirement for the files to be exactly the same as the original
-Photos can be sent quicker / faster to upload / faster to download
What is the advantage of using lossless compression over lossy compression in photo
images and video? - Answer--Maintains quality // quality better than lossy
− Original file is retained // Data is not permanently lost − A significant reduction in file
size is not required
, The file Michele is sending contains the source code for a large computer program.
Identify which type of compression would be most suitable for Michele to use and
explain why? - Answer-Lossless because the file can be restored/decompressed to the
exact same state it was before compression and because it contains a text, with the use
of lossy compression it can ruin and remove the code and cannot run the code properly.
What are the 2 methods of transmission? - Answer-Serial transmission - sends data one
bit at a time over a single channel. (use a single wire)
Parallel data transmission - when several bits are sent at a time over multiple channels.
What are the 3 directions of transmission? - Answer-Simplex transmission - allows for
data to be sent in only one direction.(unidirectional)(serial)
e.g. a microphone
Half-duplex transmission - allows data to travel in both directions but cannot occur
simultaneously (only one direction at a time) // asynchronous (cannot occur at the same
time) (serial)
e.g. two-way radio (walkie talkie)
Full Duplex - allows data to travel in both directions simultaneously(at the same time)
(parallel)
e.g. telephone
Give an example of method for errors checking? - Answer-1.Parity check
2. Checksums
3.ARQ (Automatic Repeat reQuest)
4.Check digit
5.Echo check
How parity check detect the error? - Answer-The user will clarify if the parity bytes are
going to be even/odd. All the parity bytes have to be added to be either odd or even
depend on what parity set e.g. the user had used even parity 110110100 = 1+1+1+1+1
=5
--> Error founded
If parity bit is incorrect an error is detected like as shown in the example.
Why parity check do not always detect errors? - Answer-If an even number of bits are
changed during transmission (2,4,6,8) then the Parity check is not be able to detect the
error)
A system used odd parity. Complete these following two bytes of data so they both have
odd parity:
_1111000
_0000111 - Answer-11111000
00000111
