Question

What are universal gates? Why are they called so?

Answer 1

In digital logic, a universal logic gate is a logic gate that can be used to construct all other – logic gates like AND, OR & NOT. These basic gates can be represented or created with the help of universal logic gates.

Complete step by step answer:
In Electronic physics there are AND, NOT and OR gates are the basic gates, we can create any logic gate or any Boolen expression by combining a mixture of these gates.
But NOR gates and NAND gates have the particular property that any one of them can create any logical Boolen expression if appropriately designed so they are called a universal gate.
NOR gate - Universal logic gate:
It is the combination of NOT and OR gate in such a way that output of OR gate is connected to the input of the NOT gate.
Truth table:

InputA B	OutputY=(A.B)’
0	0
0	1
1	0
1	1

Boolean Equation Y = (A.B)’
NAND universal logic gate:
It is the combination of NOT and AND gate in such a way that output of NAND gate is connected to the input of the NOT gate.

Truth table:

InputA B	OutputY=(A.B)’
0	0
0	1
1	0
1	1

Boolean Equation Y = (A.B)’

Note:
NAND and NOR gates are called universal gates because they perform all the Logic functions OR, AND and NOT.