# Difference Between Arithmetic Logical Unit (ALU) And Control Unit (CU)

The Central Processing Unit (CPU) stands as the heart and brain of modern computing devices. Within the CPU, two indispensable components work tirelessly in tandem to execute instructions and process data efficiently: the Arithmetic Logical Unit (ALU) and the Control Unit (CU).

While both units are critical to the CPU’s functionality, they actually do different roles. The ALU performs arithmetic and logical operations on data, while the CU manages the overall operation of the CPU, fetching and decoding instructions, and coordinating data flow between different units. Let us learn more about these two components:

## What is Arithmetic Logic Unit (ALU)?

An arithmetic logic unit (ALU) is the main part of the central processing unit (CPU) of a computer system. It performs all processes related to arithmetic and logic operations that need to be done on instruction words. In some processors, the arithmetic logical unit is divided into two units, an arithmetic unit (AU) and a logic unit (LU).

The (ALU) is designed in such a way that it has a direct input and output access to the processor main memory –the random access memory (RAM). Now, the input and outputs flow along an electronic path that is known as a bus. The input consists of an instruction word that contains an operation code or sometimes a format code. The operation code informs the ALU what operation to perform and the operands are used in the operation. Examples of operations that are regularly carried out by the ALU include:

• Arithmetic Operations: This is basically addition and subtraction. Addition can be substituted for multiplication and subtraction for division.
• Logical Operations:  This include NOR, NOT, OR, XOR etc.
• Bit shifting Operations:  This entails shifting the position of bits by a certain number of places to either the right or left, which is considered a multiplication operation.

In other words, the ALU has storage places for input operands, operands that are being added, the accumulated results and shifted results. The flow of data and the operations performed on them in subunits of the ALU is controlled by gated circuits. Division and multiplication are done by a series of adding or subtracting and shifting operations.

## What is Control Unit (CU)?

The control unit (CU) is a component of the central processing unit of the computer system that controls the operations of the processor. It informs the arithmetic and logic unit, the computer’s main memory and the output and input devices how to respond to the command that have been sent to the processor.  The control unit is taken to be the processor brain because it issues orders to everything and ensure that the best results are produced.

Generally, the control unit has been designed with digital circuits, encoders, decoders, logic gates and flip-flops that are arranged in a certain fixed way. There is also a special control memory that stores microprograms based on flowcharts.

The functions of the Control Unit (CU) include:

• Interprets instructions, regulate and control processor timing.
• Directs data flow through different components of the CPU.
• Handle tasks such as decoding, fletching, executing the command and storing results.