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New
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Year 10
AQA

Text file size calculations

I can calculate and compare the file size of text data when different encoding methods are used.

icon-background-square
New
New
Year 10
AQA

Text file size calculations

I can calculate and compare the file size of text data when different encoding methods are used.

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Lesson details

Key learning points

  1. A byte is the equivalent of 8 bits.
  2. Large numerical quantities can be summarised using number prefixes.
  3. Different text encoding schemes use different amounts of bits to represent each character.
  4. File size is the measure of how much binary data a file contains.

Keywords

  • Byte - a group of 8 bits

  • Number prefix - a word used in front of a number to represent a multiple of that number

  • Encoding - putting a sequence of characters into an agreed format

  • File size - a measure of how much binary data a file contains

Common misconception

The same text entered into two separate text files will always result in the same file size.

How the text has been encoded will affect the file size of a text file. ASCII uses 7 bits per character whereas Unicode uses up to 32 bits. Therefore the choice of character encoding affects the overall file size of the same text.


To help you plan your year 10 computer science lesson on: Text file size calculations, download all teaching resources for free and adapt to suit your pupils' needs...

Investigate the use of codes for character representation by developing programs that use in-built functions to convert between characters of a message and their ASCII or Unicode values. Messages could be typed in to the program and converted for display.
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This content is © Oak National Academy Limited (2025), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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6 Questions

Q1.
What is a digit of a binary number that can only be 1 or 0 called?
Correct Answer: bit, a bit
Q2.
What does a character set do?
stores images
records sound
Correct answer: matches characters to unique binary sequences
creates animations
Q3.
Match the term with its description:
Correct Answer:information,data that has been processed to provide meaning
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data that has been processed to provide meaning

Correct Answer:binary digit (bit),a digit of a binary number that can only be 1 or 0
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a digit of a binary number that can only be 1 or 0

Correct Answer:ASCII,uses 7 bits per character
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uses 7 bits per character

Correct Answer:Unicode,uses up to 32 bits per character
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uses up to 32 bits per character

Q4.
Why do computers use binary sequences?
to simplify calculations
to save space
to increase speed
Correct answer: to represent all data and instructions
Q5.
How many different characters can 7-bit ASCII represent?
64
Correct answer: 128
256
512
Q6.
What is the main advantage of Unicode over ASCII?
it uses fewer bits
Correct answer: it can represent more characters
it is faster to process
it is easier to understand

6 Questions

Q1.
Put these quantities of bytes into order, smallest to largest:
1 - byte
2 - kilobyte
3 - megabyte
4 - gigabyte
5 - terabyte
6 - petabyte
Q2.
What is a byte?
a single bit
a kind of software
Correct answer: a group of 8 bits
a type of character
Q3.
How many bits does ASCII use per character?
4 bits
Correct answer: 7 bits
16 bits
32 bits
Q4.
How does Unicode differ from ASCII?
Unicode is only for numbers
Correct answer: Unicode uses more bits to represent characters
Unicode is a type of image format
Unicode is faster to process
Q5.
If a text file contains 100 characters, what is the file size in bits using ASCII encoding?
Correct Answer: 700, 700 bits
Q6.
A text document has 50 characters. Calculate the file size in bytes when using 32-bit Unicode encoding.
Correct Answer: 200, 200 bits