C2 | Text Representation | BTEC Computing Science Extended Certificate

Download: C2 – Text Representation

Text Representation standard are needed as text and documents can be shared and viewed on many different computer systems that are being used each day.

C2: The purpose of implications of using codes to represent character sets.

  • A byte is made up of 8 bits, which can be arranged in 256 different combinations.
  • There are a common set of codes for the alphabet and numbers, which take up 62 (0-9, A-Z, a-z) of the 256 possible codes in a byte.
  • The 8-bit code for a character can be represented in denary or hexadecimal to give a sequence:
  1. For example: The letter A is stored in memory as 0 1 0 0 0 0 0 1. It can be represented as 65 in denary or 41 in hexadecimal.
  • The difference between upper and lower case characters is bit 6. (The 6th bit of the byte)
  • If the 6th bit is ‘1’, then the letter is lower case.
  • If the 6th bit is ‘0’, then the letter is upper case.
  1. ‘A’ = 0 1 0 0 0 0 0 1
  2. a’ = 0 1 1 0 0 0 0 1 (the number in bold is the 6th bit)
  • The purpose of this structure makes it easy for computer systems needing a user ID or word processors to recognise upper or lower case versions of a character by ignoring bit 6.
  • Conversion between upper and lower case is also easier by setting bit 6 to 0 or 1.
  • This adds possibilities for the font used for a character set as the appearance of numbers and alphabetic characters is easily changed using a different font.
  • A font can also make use of the other codes for shapes or accented characters

C2: The features and uses of common character sets:

ASCII: (American Standard Code for Information Interchange / ISO-IR-006)

  • Developed in 1960 (October 6th)
  • This character set is used for the English Language.
  • It is based on up to 7 bits with 128 different characters, which include control characters:
  1. Carriage Return (CR)
  2. ESC (Escape)
  • Extended ASCII uses 8 bits.

UNICODE:

  • Developed in 1987.
  • This is a character set that has been used by Windows and most websites since 1990.
  • It uses between 1 and 4 bytes for each character. This gives over a million possible characters, which makes it a good system for using multiple languages.
  • It is compatible with ASCII because they share the same codes for numbers and the alphabet.

 

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