ABSTRACT
The basic logical operations of AND, OR, XOR, and NOT are described in basic electronics and Boolean algebra texts. Although logic gates can be made from electromagnetic relays, mechanical switches, or optical components, nowadays they are normally implemented using diodes and transistors. The primitive types of gate are the AND, OR, and NOT. Additionally, the XOR gate offers an alternative version of the OR. All other Boolean operations can be implemented by combining the three primitive types. However, for convenience, other secondary types have been developed. These are called NAND (NOT plus AND), NOR (NOT plus OR), and XNOR (XOR plus NOT). The advantage of the secondary logic gates is that they require fewer circuit elements for a given function. The notion of a binary signal is based on it being in only one of two states: high or low.
