## Arithmetic and Logic Unit

<*processor*> (ALU or "mill") The part of the central
processing unit which performs operations such as addition,
subtraction and multiplication of integers and bit-wise
AND, OR, NOT, XOR and other Boolean operations. The
CPU's instruction decode logic determines which particular
operation the ALU should perform, the source of the operands
and the destination of the result.

The width in bits of the words which the ALU handles is usually the same as that quoted for the processor as a whole whereas its external busses may be narrower. Floating-point operations are usually done by a separate "floating-point unit". Some processors use the ALU for address calculations (e.g. incrementing the program counter), others have separate logic for this.

Last updated: 1995-03-24

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