Arithmetic Logic Unit (ALU)

The ALU is the centerpiece or core of the CPU architecture, where the binary calculations occur. All the other components on the CPU chip are appendanges to the execution that occurs within the ALU.

The ALU comprises logic gates that execute the instructions passed from memory and where the data stored by the registers is acted upon. A processor’s ALU is just a complex combinatorial logic circuit.

It executes arithmetic and logical operations on binary numbers and where you will find operations conducted by full-adders and half adders etc.

More specifically, the ALU is responsible for the execute phase of the fetch, decode, execute cycle.

ALU execution lifecycle

1. Inputs: The ALU receives two operands and a control signal as inputs. The operands are the data on which the operations will be performed. The control signal tells the ALU which operation it needs to perform.
2. Perform operation: The ALU carries out the requested operation. For instance, if the control signal indicates an addition operation, the ALU sums the two operands.
3. Output: The ALU then sends the operation to another part of the CPU for further processing or storage. The ALU also outputs a status bit that can be used by other parts of the CPU to make decisions. For instance if the additon results in a value that is too large to be stored, the ALU will set an overflow flag.