Character Encoding

Computer Science Hub

Lesson

Character coding schemes allows text to be represented in the computer. One such coding scheme is ASCII. ASCII uses 7 bits to represent each character which means that a total of 128 characters can be represented.


Lower case letters 26
Upper case letters 26
Numbers 10
Symbols (e.g. comma, colon) 33
Control characters 33

ASCII encoded values for some characters

A 10000012 6510
B 10000102 6610
a 11000012 9710
b 11000102 9810
"0" 01100002 4810
"1" 01100012 4910

  • ASCII has a limited character set (7 bits, 128 characters), but Unicode has 16 bits and allows many more (65K) characters.
  • Unicode provides a unique character for different languages and different platforms.
  • It allows us to represent different alphabets for instance Greek, Mandarin, Japanese, Emojis etc.
  • Unicode and ASCII are the same up to 127.


Learning Videos

For more information click on the tab below to watch a video about the lesson.


Click for video - Representing characters and character sets

Questions

  1. Using the 8-bit ASCII set, what would be the total size in bytes of the characters

    'Computer Science'?


    16 (space is a character)

  2. How many bits would 'Computer Science' require in 7-bit ASCII?


    112 bits

  3. What is meant by a character set?


    All of the characters recognised/represented by a computer system.

  4. How many characters can be represented with the 7-bit ASCII character set?


    128

  5. The eighth bit is used to give an extra 128 characters. Any character in the ASCII table can be typed using the ALT key in combination with its ASCII code. For example, if you type ALT + 065 on the numeric keypad, the letter A will appear.

    What is the binary representation of the letter A?


    0100 0001

  6. The code word is represented on the disk in a binary format, saved as:

    1000011 1000001 1000010

    Using the section of the ASCII table above, what is the code word?


    CAB

  7. What is the hexadecimal representation of the code word?


    434142

  8. Calculate the denary value representing the letter E.


    69

  9. Name one limitation of the 7-bit extended ASCII character set.


    Only 128 characters can be represented, so there is no way of representing characters from large character sets such as Japanese/Chinese.

  10. Explain how these limitations can be overcome.


    By using more bits for each character / Unicode which uses 16 bits

    so that there are more available combinations to store the new characters



Go Back