Logic gates

OR gate

Boolean expression Y=A+B

AND gate

Boolean expression Y=A.B

NOT gate

Boolean expression Y=

NAND gate

Boolean expression=

NOR

Boolean expression Y=

XOR

Boolean expression Y=

NAND and NOR as the basic building blocks

Any logic gate can be constructed by using only NAND gates or only NOR gates. Therefore these two gates are called the building blocks.