All digital systems can be constructed by only three basic logic gates. These basic gates are called the AND gate, the OR gate, and the NOT gate. Some textbooks also include the NAND gate, the NOR gate and the EOR gate as the members of the family of basic logic gates. The description of the operations of these gates are listed below [Ref.2]:

AND gate

The AND gate is a circuit which gives a high output (logic 1) if all its inputs are high. A dot () is used to indicate the AND operation. In practice, however, the dot is usually omitted.

OR gate

The OR gate is a circuit which gives a high output if one or more of its inputs are high. A plus sign (+) is used to indicate the OR operation.

NOT gate

The NOT gate is a circuit which produces at its output the negated (inverted) version of its input logic. The circuit is also known as an inverter. If the input variable is A, the inverted output is written as .

NAND gate

The NAND gate is a NOT-AND circuit which is equivalent to an AND circuit followed by a NOT circuit. The output of the NAND gate is high if any of its inputs is low.

NOR gate

The NOR gate is a NOT-OR circuit which is equivalent to an OR circuit followed by a NOT circuit. The output of the NOR gate is low if any of its inputs is high.

EOR gate

The Exclusive-OR gate is a circuit which gives a high output if either of its two inputs is high, but not both. A encircled plus sign () is used to indicate the EOR operation.