Starter - Page 6 Sending Secret messages

Date =
Title = Characters
Objectives:
  • explain the use of binary codes to represent characters
  • explain the term character set
  • describe with examples (for example ASCII and Unicode) the relationship between the number of bits per character in a character set and the number of characters which can be represented.

Keywords:
  • Character set
  • ASCII
  • EBCDIC
  • Unicode

Characters

Every time a character is typed on a keyboard a code number is transmitted to the computer. The code numbers are stored in binary. Different sets of codes are available for different types of computer. PCs use a character set called ASCII, American Standard Code for Information Interchange. A character set is the group of characters that can be decoded. ASCII uses 7 bits to encode each character. The biggest number you can have with seven bits is 1111111 in binary (127 in denary). The smallest number you can have with seven bits is 0000000 (0 in denary!). This means you can have 128 different characters in the character set (using codes 0 - 127)
Other character encoding systems include:
  • Unicode - a 16-bit encoding system that has 2 to the power of 16 (65,536) different characters in its character set
  • EBCDIC (pronounced eb-sid-ic): Extended Binary Coded Decimal Interchange Code, an 8-bit encoding system that has 2 to the power of 8 (256 - including 0) different characters in its character set.

Watch the videos and take the short tests, then answer the questions below in your books (25 mins)
http://www.cambridgegcsecomputing.org/representation-of-data-in-computer-systems-main > 35. Character Sets

Questions:

Theory links:


1.Explain what is meant by a ‘character set’. (3 marks)
2.
  • (a) The first edition of the ASCII code was published in 1963 and it was based on an earlier code. What was this earlier code used for? (1 mark)
  • (b)
    • (i) How many bits are used in the original ASCII code? (1 mark)
    • (ii) How many characters can be encoded using this number of bits? (1 mark)
  • (d) Not all of the characters are printable. What are the others called and what are they used for? (2 marks)
3. Many manufactures extended the ASCII code by using the eighth bit.
  • (a) How many characters can be represented using 8 bits? (1 mark)
  • (b) Why did the use of extended ASCII codes cause problems for users? (2 marks)
4.
  • (a) Why was the UNICODE character set developed? (2 marks)
  • (b) How many bits are used to code a character in this character set? (1 mark)
5. Write down the characters represented by the following bytes. (3 marks, 1 each)
  • (a) 01000011
  • (b) 01100001
  • (c) 01110100
6. Write down the 8 bit binary code and the denary representation for the following characters. (3 marks, 1 for each)
  • (a) M
  • (b) d
  • (c) s
7. Write out your name in Binary.

EXTENSION:



Decoding Activity:

http://www.cambridgedigital.com/mooc/html/jan14/35_Activity1/35_Activity1.html
Use this link to help: http://www.cambridgedigital.com/mooc/html/jan14/35_Activity2/35_Activity2.html

Plenary

http://www.bbc.co.uk/education/guides/zp73wmn/test