Arithmetic and Logic Unit

processor (ALU or "mill") The part of the centralprocessing 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-pointunit". Some processors use the ALU for address calculations

(e.g. incrementing the program counter), others have

separate logic for this.

(1995-03-24)