Binary Subtraction

Subtracting Binary Numbers

• Computers use addition process to implement subtraction.
• Computers have adder circuitry but there is no separate circuitry for subtractors.
• To implement A-B, the computer takes the 2’s complement of B and then adds it to A.
• 2’s Complement: Invert all the bits of a binary number and then add 1 to the result.
• Inverting (changing all 0s to 1s and 1s to 0s) all the bits of a binary number is called 1’s complement.

Take 2’s complement of 10011101.

	10011101	binary number
	01100010	1’s complement
+	1
=	01100011	2’s complement

Subtract 10011101 from 10011111.

10011111 – 10011101
	= 10011111 + 2’s complement of 10011101
	= 10011111 + 01100011
	= 00000010 (Discard the last carry)
	= 10

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Related topics:
Counting in Decimal, Binary, Hexadecimal   |   Binary Addition   |   Hex Addition   |   Hex Subtraction   |   Hexadecimal to Decimal Conversion

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List of topics: Microcomputer

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