Question

What are universal gates? Why are they called so?

Answer 1

Hint: There are two universal gates. All the other basic logic gates like AND, OR, etc. can be created using these gates. These basic gates can be represented in the form of these universal gates.

Complete step by step answer:
Logic gates are the circuits which can have one or more inputs but only one output. These are based on a certain logic. Hence, these are called logic gates. As per their logic, they are named as AND, OR, NOT, etc.
Universal gates are the logic gates that can be used to create all the other logic gates. NAND and NOR are called the Universal gates. Combining these gates other basic gates are developed. Any logic gate can be created using a mixture of basic gates. But using a single type of NAND or NOR gate a basic gate can be created. Hence, they are called Universal gates. Any Boolean expression can be expressed using these universal gates.

Above figure shows a NOR Gate. It is a combination of OR and NOT gate. The output of the OR gate is given to the NOT gate as an input. Output from NOT gate is high only when all the inputs to the OR gate are low. The outputs of the NOR gate and OR gate are complement of each other.

Above figure shows a NAND Gate. It is a combination of OR and AND gate. The output of the AND gate is given to the OR gate as an input. Output from the NOT gate is low only when all the inputs to the AND gate are high. The outputs of the NOR gate and OR gate are complement of each other.

Note:
OR gate can be created by combining AND gate and NOT gate. Similarly, AND gate can also be created using OR and NOT gate. However, AND and OR gate cannot be combined to give any other logic gate. Hence, they are not called Universal Gates.