1. Nat 4/5 Computing Science Data Representation Lesson 3: Storing Text
Computer Systems
Nat 4/5 Computing Science
Data Representation
Lesson 3:
Storing Text

2. REVISION What is the system used to store real numbers?
Convert into a decimal number
Convert 23 into binary.
Using this scientific notation value, 3.8 x 108 , describe what is mean by a mantissa and exponent

3. ANSWERS Floating Point representation 1100 1100 = 204 23 = 0001 0111
In the number 3.8 x108 the mantissa would be 3.0 with the exponent being 8

4. Lesson Aims By the end of this lesson you will be able to:
Describe how text is stored
Explain and give an example of an ASCII character.
Describe how many bytes are needed to represent a single character using ASCII.
Describe what is meant by the term character set.
Give an example of why we need different character sets.
Explain what Unicode is
Describe how many bytes are needed to store a single character using Unicode.

5. A question… Computers can only use binary digits i.e. 0’s and 1’s.
Nat 4/5
A question…
Computers can only use binary digits i.e. 0’s and 1’s.
How can we store text?
By storing them as binary numbers….

6. ASCII Codes Each character on a keyboard has its own ASCII code.
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ASCII Codes
Each character on a keyboard has its own ASCII code.
ASCII code = a binary value that represents a character
American Standard Code for Information Interchange
All computers can exchange information and understand it

7. ASCII example For example A = 100 0001 (65)
Each ASCII value uses 7 bits but it is assumed that 1character =1 byte

8. ASCII Table An extract of the ASCII Table is shown below:
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ASCII Table
An extract of the ASCII Table is shown below:
The ASCII table has 128 values (27=128) so there are codes for 128 different characters can be used
Code
Symbol 48 78 N 64 @ 97 a 49 1 79 O 65 A 98 b 50 2 80 P 66 B 99 c 51 3 81 Q 67 C
100 d 52 4 82 R 68 D
101 e 53 5 83 S 69 E
102 f

9. Nat 4/5
ASCII Codes
96 out of 128 ASCII codes are used to store characters. This includes:
Upper and lower case letters A-Z, a-z
Punctuation and other symbols , : ; £ $ %
10 codes for numbers, 0 to 9
Spacebar has a code too = code 32

10. Nat 5
Extended ASCII
Many computer systems use a form of ASCII called Extended ASCII
8-bit code that allows (28) different characters

11. Extended ASCII
It includes additional characters used in European countries like é á æ ß
Also © ≠ ≤ ≥ ™ ÷
Some Extended ASCII characters are shown here 

12. Nat 4/5
Character Set
The character set is the name given to the complete set of characters that the computer can represent.
Different character sets are used to represent different languages

13. UNICODE Unicode is a 16-bit code which allows 65,536 characters
Nat 5
UNICODE
Unicode is a 16-bit code which allows 65,536 characters
Has codes for every language in the world
Includes cosed for character-based alphabets e.g
Chinese and Japanese

14. Summary Text is stored in the computer using ASCII values
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Summary
Text is stored in the computer using ASCII values
1 ASCII Value = 1 byte of memory
ASCII allows 128 characters
Extended ASCII allows 256 characters
The character set is the name given to the entire set of characters that the computer can use
Unicode uses 2 bytes per characters and allows 65,536 characters – for all languages

15. Pupil Task: Worksheet 3
Complete the answers to this task in your jotter.