EasyCS

Introduction to Boolean logic

 

In this introduction to Boolean logic, we’ll cover the operation of a transistor, the ‘flip-flop’ arrangement, logic gates, truth tables and how it all fits together into computer memory and our everyday lives too.

 

The operation of a transistor and the “flip-flop” arrangement of transistors being used to create computer memory

 

A transistor is a switch that can be in either an on state or an off state. This means a transistor can represent 1 bit of information at a time, either a 0 when it is off or a 1 when it is on. We can use an electric current to flip the transistor from one state to another. As it will always flip from on to off or off to on this pattern is known as the flip flop arrangement.

Using this flip flop arrangement, we can represent binary bits one single bit at a time. Computer chips have hundreds of millions of these transistors all using this flip-flop arrangement to transmit hundreds of millions of bits incredibly quickly. A transistor doesn’t have to keep changing state though. A transistor can be kept in its current state by feeding its output back into its input. This means that a resistor can keep representing the 1 or 0 which is how computer memory uses them.

 

Logic gates and Truth tables briefly explained

 

The term ‘boolean logic’ refers to the binary representation of transistors and logic gates inside a CPU. A logic gate is a fundamental piece of a digital circuit. It will take one or more inputs and produce a specific output that will correspond with the specific combination of inputs and the type of logic gate it is. There are 7 logic gate types but three are more common than the others. The three most common types of logic gates are:

  • AND
  • OR
  • NOT

 

A truth table is a simple table that can be used to work out the output signals for specific combinations of input signals, which will naturally differ depending on the logic gate those inputs are being applied to.

An example of a simple truth table for a NOT gate can be seen below:

A not gate is a very simple logic gate, it takes an input and outputs the exact opposite signal as can be seen in the table above.