Secret Codes
How computers store text: character sets and character codes, ASCII as a 7-bit set of 128 characters with letters in order, and Unicode as a larger set that covers every language and emoji but needs more bits per character.
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How text becomes numbers
A computer only stores numbers, so every letter and symbol is given a number called its character code. The full list of characters and their codes is a character set. This module works through ASCII, the small 7-bit set used for English, and Unicode, the huge set that covers every language and emoji, and how to do simple sums with character codes.
Encoding words to know
Learn these before you crack the codes.
ASCII against Unicode
A bigger character set costs more storage.
Tie the bits to the characters
In the exam, tie the number of bits to the number of characters. With only 7 bits, ASCII can label just 128 characters, fine for English but not for other alphabets. Unicode spends more bits per character, so it can label far more, covering every language and emoji, but the text then takes up more room. For code sums, the letters are numbered in order, so the letter just after one is a single code higher.
Match the term
- character set
- ASCII
- Unicode
- character code
- the list of characters a computer can use
- a 7-bit set of 128 characters
- a larger set covering all languages
- the number standing for a character
Match the fact
- 7 bits in ASCII
- the codes for A, B and C
- Unicode
- coding more characters
- label 128 characters
- come one after another
- can store emoji and other alphabets
- needs more bits for each one
Why was Unicode created?
Why was Unicode created when ASCII already existed?
- To code characters from all the world languages
- To make every file much smaller
- To remove all letters from computers
- To replace binary numbers
True about character sets
Select the TWO true statements about character encoding.
- ASCII uses 7 bits and codes 128 characters
- Unicode needs more bits per character than ASCII
- The codes for A, B and C are in a random order
- ASCII can store every language and emoji
Work out the code
In ASCII the letter A has the code 65, and the letters run in order, so B is 66 and C is 67. Add 3 to 65 to find the code for the letter D. What is the answer?
Order the story of encoding
Put these steps of character encoding in order, earliest first.
- Every character is given a number in the character set
- The number is stored as bits in the computer
- ASCII uses 7 bits for 128 characters
- Unicode uses more bits for far more characters
Complete the rules
The list of characters a computer can use, each with a number, is a character _____. A 7-bit set of 128 characters is _____. A larger set covering all languages is _____. The number that stands for a character is its character _____.
Spot the true encoding facts
Tap the TWO true statements about character encoding.
- ASCII uses 7 bits to code 128 characters
- Unicode can represent many languages and emoji
- ASCII can store every world language
- character codes for letters are in random order
Pick the answer
Read each case and choose the best answer.
- A program needs to display Chinese, Arabic and emoji as well as English. Which character set does it need?
- In a character set the letter A has the code 65. What is the code for the letter B?
- Why does storing text in Unicode usually take more space than storing it in ASCII?
Explain character encoding
Explain the difference between ASCII and Unicode and why Unicode is needed.
- Explain what a character set and a character code are
- Explain how many bits and characters ASCII uses
- Explain why Unicode exists and its trade-off in storage