NAND Gate
This is an AND gate followed by a NOT gate. If inputs A and B are both ‘1’, the output Y is not ‘1’. The gate gets its name from this NOT AND behaviour. Figure shows the symbol and truth table of NAND gate.
NAND gates are also called Universal Gates since by using these gates you can realise other basic gates like OR, AND and NOT. as shown below :
NOR Gate
It has two or more inputs and one output. A NOT- operation applied after OR gate gives a NOT OR gate (or simply NOR gate). Its output Y is ‘1’ only when both inputs A and B are ‘0’, i.e., neither one input nor the other is ‘1’. The symbol and truth table for NOR gate is given in Fig.
NOR gates are considered as universal gates because you can obtain all the gates like AND, OR, NOT by using only NOR gates as shown in following fig.
