**Logic gates** are the fundamental building blocks of circuits. **Circuits** are used to perform operations in a computer system. They are mainly used in the arithmetic logic unit known as **ALU**. 

There are 5 main logic gates. 

* AND
* OR
* NOT 
* NOR
* NAND

These logic gates take inputs and give a single output.


# AND gate
The **AND** gate gives $1$ as an output when all the inputs are $1$. If there are any $0$'s in the input, the AND gate gives $0$ as an output. Think of it as multiplication between $0$ and $1$. 


# OR gate
The **OR** gate gives $1$ as an output when at least one of the inputs is $1$. If all inputs are $0$, the output is $0$. Think of it as addition between $0$ and $1$.

# NOT gate
**NOT** is a simple gate that takes in a single input and reverses its value. Whatever the input, this gate outputs the opposite (i.e., if $1$ is inputted, it gives $0$ as the output). 

# NOR gate
The **NOR** gate is opposite to the OR gate. It gives $1$ as an output whenever all inputs are $0$ (i.e., $1$ is not an input).  

# NAND gate
The **NAND** gate gives $1$ as an output when there is a single $0$ as an input. It gives $0$ as an output whenever all inputs are $1$. NAND is opposite of AND. 