Boolean Logic Diagrams (AQA GCSE Computer Science): Revision Note

What is Boolean logic?

• Boolean logic is used in computer science and electronics to make logical decisions

• Boolean operators are either TRUE or FALSE, often represented as 1 or 0

• Inputs and outputs are given letters to represent them

• To define Boolean logic we use special symbols to make writing expressions much easier 

Boolean Logic Diagrams

What are logic gates?

• Logic gates are a visual way of representing a Boolean expression

• The logic gates covered in this course are:

  • AND

  • OR

  • NOT

  • XOR

AND

Expression operator	Circuit symbol	Explanation
(A AND B)		Returns TRUE only if both inputs are TRUE  TRUE AND TRUE = TRUE Otherwise = FALSE

OR

Expression operator	Circuit symbol	Explanation
(A OR B)		Returns TRUE if either input is TRUE  TRUE OR FALSE = TRUE  FALSE OR FALSE = FALSE

NOT

Expression operator	Circuit symbol	Explanation
(NOT A)		Reverses the input value NOT TRUE = FALSE NOT FALSE = TRUE

XOR (exclusive OR)

Expression operator	Circuit symbol	Explanation
(A XOR B)		Returns TRUE if either input is TRUE but NOT both TRUE OR FALSE = TRUE  FALSE OR FALSE = FALSE TRUE OR TRUE = FALSE