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

REVISION What is the system used to store real numbers? Convert 1100 1100 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

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

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.

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….

ASCII Codes Each character on a keyboard has its own ASCII code. Nat 4/5 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

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

ASCII Table An extract of the ASCII Table is shown below: Nat 4/5 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

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

Nat 5 Extended ASCII Many computer systems use a form of ASCII called Extended ASCII 8-bit code that allows 256 (28) different characters

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

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

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

Summary Text is stored in the computer using ASCII values Nat 4/5 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

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