IGCSE COMPUTER SCIENCE EXAMS QUESTIONS AND ANSWERS
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IGCSE COMPUTER SCIENCE
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IGCSE COMPUTER SCIENCE
IGCSE COMPUTER SCIENCE
As humans, we process ........data, but a computer cannot process this type of data. For a computer to be able to process data it needs to be converted to ............data. As humans, we mostly use a ............ number system; this is a base ........ number system. Comput...
IGCSE COMPUTER SCIENCE
As humans, we process ........data, but a computer cannot process this type of data. For a computer to be able to process
data it needs to be converted to ............data. As humans, we mostly use a ............ number system; this is a base ........
number system. Computers use a .............number system; this is a base ..........number system.
Complete the sentence by using these words:
denary, 2, 10, binary, analogue, digital - Answer- analogue
digital
denary
10
binary
2
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. It compresses by
reducing resolution and colour palette that is indistinguishable, so each pixel requires fewer bits and removes the detail that
is unnecessary, like sound that humans can't hear.
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
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 // asynchronous (cannot
occur at 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
How checksum detected the error? - Answer- The sender computers use the block of data, and a predefined
mathematical algorithm, to calculate a checksum value. The sender sends a checksum with data. The receiver receives data
and the checksum is recalculated. The two checksum values are compared by the receiving computer. Error detected if
checksums are different.
Mark scheme:
• Calculation performed on data (to get the checksum) • Checksum sent with data
• Checksum recalculated after transmission • Comparison made between checksum before and checksum after
transmission
• Error detected if checksums are different
How ARQ detected the error? - Answer- ARQ uses acknowledgement and time out. The sender transmits a block of data.
The sender waits for an acknowledgement. If no response/acknowledgement or any errors occur(negative
acknowledgement is used), the request(with data) is repeated till the data is sent correctly or the request time out.
Find the check digit for this identification number
**-multiply each digit by its digit position
-add up the results of the multiplication
-divided the answers by 11
-if the remainder is 0, the identification number and check digit are valid(correct)**
What is USB? - Answer- Universal Serial Bus. USB uses serial transmission for sending data externally.
(USB is off-line storage)
Leonard has a new laser printer to print letters for his business. Leonard connects his printer to his computer using the USB
port.
Give 3 benefits of using the USB port to connect the printer to the computer. - Answer- -It is a universal standard
− It can't be inserted the wrong way around
− Supports different transmission speeds
− Automatically detects if correct driver installed
What is integrated circuits? - Answer- Integrated Circuits (IC) uses parallel data transmission for sending data internally.
(also RAM)
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