Half Adder

What Does Half Adder Mean?

A half adder is a type of adder, an electronic circuit that performs the addition of numbers. The half adder is able to add two single binary digits and provide the output plus a carry value. It has two inputs, called A and B, and two outputs S (sum) and C (carry). The common representation uses a XOR logic gate and an AND logic gate.


Techopedia Explains Half Adder

A half adder is used to add two single-digit binary numbers and results into a two-digit output. It is named as such because putting two half adders together with the use of an OR gate results in a full adder. In other words, it only does half the work of a full adder.

The adder works by combining the operations of basic logic gates, with the simplest form using only a XOR and an AND gate. This can also be converted into a circuit that only has AND, OR and NOT gates. This is especially useful since these three simpler logic gate ICs (integrated circuits) are more common and available than the XOR IC, though this might result in a bigger circuit since three different chips are used instead of just one.

Half Adder truth table:

A (input) B (input) C (output) S (output)
0 0 0 0
1 0 0 1
0 1 0 1
1 1 1 0

circuit diagram for a half adder


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Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.