Arithmetic and Logic Unit definition 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
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.