Central Processing Unit (CPU) Explained

The central processing unit (CPU) is one of the most important components of computer hardware. In this article, we look at CPU components and how these parts work to process data.

What is the CPU?

CPU is the brain of a computer that processes all instructions you enter into a computer. The CPU is also popularly known as a microprocessor,  chip, and central processor. Therefore, we will use these terms interchangeably.

A picture of CPU

This picture shows how a computer CPU looks like. If you open your desktop or laptop, you will find this component mounted on the motherboard.

Several pins you see in the picture connect the processor to the motherboard. Therefore, you may not see the pins when you open your computer.

The CPU Components

A computer CPU is composed of four main components that include Control Unit (CU), Arithmetic Logic Unit (ALU), Registers, and Buses.

Arithmetic Logic Unit (ALU)

ALU is a computer mathematician for two main reasons. First, ALU performs all mathematical operations that include addition, subtraction, multiplication, division, and comparison.

Secondly, ALU also performs logical operations like IF, OR, Else If, NOR decisions. ALU has two inputs say A and B. Each of the inputs is an 8-bit data. Let’s take an add operation. The CU will instruct ALU to add A and B.

Whenever ALU performs any operation, it outputs the answer. Then another challenge comes in. ALU doesn’t have an internal memory to store the output of the operation.


A register is a temporary memory within CPU that stores the ALU operations output. For instance, when ALU adds two numbers say A and B, the result is stored in a register awaiting further instructions from the CU.

A register can only store one output or data set at a time. Therefore, the CPU has several registers to store different outputs awaiting.

A register is connected to the CU using Enable and Set wires. Therefore, each register within the processor is connected to the Control Unit via Enable and Set buses.

The Set wire is meant to clear the contents of a register. Therefore, a register stores ALU output until the CU sends a set signal.

An Enable signal from CU to a register saves data into a register. For example, if CU needs to store data into one of the registers, it will activate enable wire. The data held on the bus will be saved in the register.

By so doing, a CPU can perform many operations with a very short period of time. That makes computer process instructions faster.


Buses are wires connecting various components in CPU. Note that buses are used throughout the computer circuitry.

We have seen that a CPU is composed of the ALU, CU, and Registers. These components need to exchange data with one another depending on the instructions send by the CU.

To achieve this, the components are interconnected using wires. These wires are technically referred to as the bus. However, these are not ordinary cables you see around. A bus is a cable with 8 wires in it. Below is why.

CPU processes information in terms of bytes. A byte is a collection of 8 bits. In binary computing, a bit is either 0 or 1.

A bus carries a byte is composed of 8 bits that include 0s and 1s. Therefore, each register stores one byte of information.

Control Unit (CU) 

The CU can be interpreted as the brain of the CPU since it coordinates all operations within the processor.

A CU extracts instructions from the RAM, decode and execute these instructions according to the specified commands you feed them.

The CU then instructs the ALU to perform either a logic or arithmetic operation. ALU then stores the output in a Register as explained earlier.

The CU then may use the ALU output to perform other operations depending on the instructions.

For instance, the CU may need to send the ALU output to the output devices like the keyboard or the monitor. If so, CU will enable the register to instruct the Register to send the data to the output devices.

How CPU Works

As explained in our computer hardware article, CPU works closely with the Random Access Memory (RAM).

Being the brain of the computer, the processor performs billions of operations in a second. Such operations obviously require high precision and speed. Let’s understand CPU speed first. 

CPU Processing Speed 

CPU speed measured in GigaHertz (GHz). Giga is a mathematical term that means a billion. Whereas Hertz is a technical term that means times per second. 

1GHz refers to a billion times per second. CPU turns a clock a thousand times each second thus the processor can execute a billion processes each second.

A CPU size is measured in multiples of GHz. Common capacities include 1.80 GHz, 2.0GHz, 2.5GHz, and 3.30GHz. The highest CPU speed currently in production is IBM zEC12 whose rate is 5.5GHz.

A motherboard has special CPU slots. Therefore, a processor chip easily fits in the motherboard. The CPU slots are then connected to other components like RAM through Buses.

CPU Clock and Synchronization

To keep the operations coordinated, CPU use a clock. A clock is simply a wire that turns on and off at a steady rate to produce a clock signal.

The clock signal is a square wave that has rising and falling edges. One square wave containing one edge rise and one falling edge is referred to as the clock pulse.

Then CPU then uses each clock pulse to initiate various operations. Most CPUs use the rising clock rising edge to start operation. Others may use the falling edge.

Let’s say a CPU is using the falling edge. This means all CU operations will start when a rising clock signal is initiated.

This means all operations within the chip will start at the same time in what is referred to as synchronization.

CPU Chip Manufacturers

Intel Incorporation and Advanced Micro Device (AMD) Incorporation are the leading CPU chips manufacturers in the world. Other smaller manufacturers include IBM, ARM holdings, Futjisu, Broadcom inc., Nvidia, and Samsung among others.

Most Personal Computer manufacturers use Intel processors. Therefore, you will find that most desktops and Laptops use Intel processors.

Most people are familiar with Intel processors that include Core i3, Core i5, and Core i7.


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