Character Sets (Cambridge (CIE) IGCSE Computer Science)

Revision Note

Robert Hampton

Written by: Robert Hampton

Reviewed by: James Woodhouse

Character Sets

What is a character set?

  • A character set is all the characters and symbols that can be represented by a computer system

  • Each character is given a unique binary code

  • Character sets are ordered logically, the code for ‘B’ is one more than the code for ‘A’

  • A character set provides a standard for computers to communicate and send/receive information

  • Without a character set, one system might interpret 01000001 differently from another

  • The number of characters that can be represented is determined by the number of bits used by the character set

  • Two common character sets are:

    • American Standard Code for Information Interchange (ASCII)

    • Universal Character Encoding (UNICODE)

ASCII

What is ASCII?

  • ASCII is a character set and was an accepted standard for information interchange

  • ASCII uses 7 bits, providing 27 unique codes (128) or a maximum of 128 characters it can represent

ASCII character set containing character, ASCII and binary codes
  • ASCII only represents basic characters needed for English, limiting its use for other languages

Extended ASCII

  • Extended ASCII uses 8 bits, providing 256 unique codes (28 = 256) or a maximum of 256 characters it can represent

  • Extended ASCII provides essential characters such as mathematical operators and more recent symbols such as ©

Limitations of ASCII & extended ASCII

  • ASCII has a limited number of characters which means it can only represent the English alphabet, numbers and some special characters

    • A, B, C, ………, Z

    • a, b, c ,.............,z

    • 0, 1, 2,........, 9

    • !, @, #, …..

  • ASCII cannot represent characters from languages other than English

  • ASCII does not include modern symbols or emojis common in today's digital communication

UNICODE

What is UNICODE?

  • UNICODE is a character set and was created as a solution to the limitations of ASCII

  • UNICODE uses a minimum of 16 bits, providing 216  unique codes (65,536) or a minimum of 65,536 characters it can represent

  • UNICODE can represent characters from all the major languages around the world

Examiner Tips and Tricks

 Exam questions often ask you to compare ASCII & UNICODE, for example the number of bits, number of characters and what they store

ASCII vs UNICODE

 

ASCII

UNICODE

Number of bits

7-bits

16-bits

Number of characters

128 characters 

65,536 characters

Uses

Used to represent characters in the English language.

Used to represent characters across the world.

Benefits

It uses a lot less storage space than UNICODE. 

It can represent more characters than ASCII. 

It can support all common characters across the world.

It can represent special characters such as emoji's.

Drawbacks

It can only represent 128 characters. 

It cannot store special characters such as emoji's.

It uses a lot more storage space than ASCII. 

Worked Example

The computer stores text using the ASCII character set.
 

Part of the ASCII character set is shown:

Character

ASCII Denary Code

E

69

F

70

G

71

H

72

(a)

Identify the character that will be represented by the ASCII denary code 76 [1]

(b)

Identify a second character set [1]

Answers

(a) L (must be a capital)

(b) UNICODE

Last updated:

You've read 0 of your 10 free revision notes

Unlock more, it's free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Robert Hampton

Author: Robert Hampton

Expertise: Computer Science Content Creator

Rob has over 16 years' experience teaching Computer Science and ICT at KS3 & GCSE levels. Rob has demonstrated strong leadership as Head of Department since 2012 and previously supported teacher development as a Specialist Leader of Education, empowering departments to excel in Computer Science. Beyond his tech expertise, Robert embraces the virtual world as an avid gamer, conquering digital battlefields when he's not coding.

James Woodhouse

Author: James Woodhouse

Expertise: Computer Science

James graduated from the University of Sunderland with a degree in ICT and Computing education. He has over 14 years of experience both teaching and leading in Computer Science, specialising in teaching GCSE and A-level. James has held various leadership roles, including Head of Computer Science and coordinator positions for Key Stage 3 and Key Stage 4. James has a keen interest in networking security and technologies aimed at preventing security breaches.