 Logic Gates of Computer (AND OR NOT NAND NOR EXOR EXNOR)

Friends. You know what is the use of Logic Gates in computer ? Normally “logic” means IQ. As you know that computer does not have it’s own IQ. Yes it is true that Computer IQ level is zero. Computer cannot do anything without instruction. We people create(coding) the instruction and computer follow these instructions. So Computer has it’s own mechanism to produce logic for itself. So Logic Gates are used in computer for this task.

Definition of Logic Gates(Logic Circuit)

Digital systems are said to be constructed by using logic gates. There are so many types of logic gates in computer. These gates are the AND, OR, NOT, NAND, NOR, EXOR and EXNOR gates. The basic operations are described below with the aid of Logic Gate truth table.

(1) AND gate

The AND gate is an electronic circuit that gives a high output (1) only if all its inputs are high.  A dot (.) is used to show the AND operation i.e. A.B. (2) OR gate

The OR gate is an electronic circuit that gives a high output (1) if one or more of its inputs are high.  A plus (+) is used to show the OR operation. (3) NOT gate

The NOT gate is an electronic circuit that produces an inverted version of the input at its output.  It is also known as an inverter.  If the input variable is A, the inverted output is known as NOT A. This is also shown as A’, or A with a bar over the top, as shown at the outputs. (4) NAND gate

This is a NOT-AND gate which is equal to an AND gate followed by a NOT gate.  The outputs of all NAND gates are high if any of the inputs are low. The symbol is an AND gate with a small circle on the output. The small circle represents inversion. (5) NOR gate

This is a NOT-OR gate which is equal to an OR gate followed by a NOT gate.  The outputs of all NOR gates are low if any of the inputs are high. The symbol is an OR gate with a small circle on the output. The small circle represents inversion. (6) EXOR gate

The ‘Exclusive-OR‘ gate is a circuit which will give a high output if either, but not both, of its two inputs are high.  An encircled plus sign ( ) is used to show the EOR operation. (7) EXNOR gate

The ‘Exclusive-NOR’ gate circuit does the opposite to the EOR gate. It will give a low output if either, but not both, of its two inputs are high. The symbol is an EXOR gate with a small circle on the output. The small circle represents inversion. All Logic Gates Output in One Diagram :  The NAND and NOR gates are called Universal Logic Gates since with either one the AND and OR functions and NOT can be generated.

Also Check “BIOS in computer and Computer’s Booting Process”.