The ALU is the centerpiece or core of the [CPU](/Computer_Architecture/CPU/CPU_architecture.md) 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](/Electronics_and_Hardware/Digital_circuits/Logic_gates.md) 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](/Electronics_and_Hardware/Digital_circuits/Half_adder_and_full_adder.md) etc.
More specifically, the ALU is responsible for the _execute_ phase of the [fetch, decode, execute cycle](/Computer_Architecture/CPU/Fetch_decode_execute.md).
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.
