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The Central Processing Unit and Its Internal Components

Patrick, a computer technician, is a dedicated writer who wishes to make the world better by informing individuals who seek more knowledge.

In any computer system, the most essential component is the processor or the CPU (Central Processing Unit), which is also commonly referred to as the microprocessor. The computer processor processes information and interfaces with many other system elements to retrieve data to be processed and return the data that has been processed.

Generally, the processor performs the following functions in a computer system:

  • It fetches, decodes and executes instructions obtained from software programs
  • Performs arithmetic calculations
  • Controls and supports the timing of each operation

The speed of the computer processor is a major factor in determining the performance of the PC, that is, how fast instructions will be executed.

An AMD Processor

An AMD's Processor

An AMD's Processor

The Processor or the Central Processing Unit

The CPU is also one of the most expensive components on the motherboard. It is a very delicate device and sensitive to ESD, thus it should be handled with care. The processor itself is a flat plate of silicon made up of millions of transistors etched on to the silicon plate to form a huge computer logic circuit.

A ceramic cover is placed over the micro-circuit to protect it and to conduct heat away to the heat sink. This protective ceramic covering will have print information of the processor type, speed, and other details.

A List of CPU Manufacturers

Though Intel is the best-known company in processor manufacturing, we have a wide range of processors from other manufacturers such as:

  • Advanced Micro Devices (AMD)
  • VIA
  • Integrated Device Technology (IDT) - acquired by VIA
  • Qualcomm
  • IBM
  • Samsung
  • Motorola
  • Hewlett-Packard (hp)
  • Dell
  • Acer
  • Cyrix
  • Media Tek

Each of these companies offers competitively priced processor chips with comparable performance to Intel processors. They also offer compatibility with Microsoft operating system software. In terms of processor technology advancement, these other manufacturers are also not left behind.

How the Central Processing Unit Operates

The computer processor fetches, decodes, and executes program instructions. A computer program consists of a series of steps called instructions which tell the computer what to do. Each instruction can be a basic arithmetic calculation or a logic operation. Before the program can be executed, it is loaded into the working space (memory).

It is the job of the microprocessor, which is controlling the computer to fetch a program instruction from the memory, decode the instruction and then carry out any action that might be needed which is the execution process. It is the responsibility of the processor inside the computer to carry out the fetch-decode-execute cycle over and over again operating from the instructions it obtains from the main memory.

This fetch - decode - execute cycle is often referred to as the fetch-execute cycle.

The CPU uses a timing signal to be able to fetch and execute instructions. The timing signal is provided by the system clock. The clock speed is measured in Hz (cycles per second). In early processors, speed was measured in Megahertz (MHz) is one million hertz (1 million cycles per second). Most of the computers we have today operate in the GHz (Gigahertz) range. The clock speed varies from one computer processor to another.

Key Components Found Inside the CPU

Arithmetic and Logic Unit (ALU)
This is the brain of the microprocessor. The ALU performs basic arithmetic calculations like adding, subtracting, multiplication and division of figures, it also performs logical operations like the comparison of figures.

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Internal parts of the processor

Internal parts of the processor

Control Unit (CU)

As the name suggests, this component controls all the functions that take place inside the processor itself. It instructs the ALU on which arithmetic and logical operation is to be performed. It acts under the direction of the system clock and sorts out all the internal data paths inside the processor to make sure that data gets from the right place and goes to the right place.

The Register

Register, also sometimes known as the accumulator, is a temporary storage position where data coming from RAM heading to the processor for execution and data coming from the processor after processing is held. Thus a register is a local storage area within the processor that is used to hold data that is being worked on by the processor.

Internal Registers (Internal Data Bus)

This is the bus connecting the internal components of the processor to the motherboard. The size of the internal registers indicates how much information the processor can operate on at one time and how it moves data around internally within the chip. This is sometimes also referred to as the internal data bus. A register is a holding cell within the processor; for instance, the processor can add numbers in two different registers, storing the result in a third register. The register size determines the size of data on which the processor can operate.

External Data Path

This is the path (bus) used to fetch data from memory to the processor. In some cases, the internal and external data buses are the same bit-size but in others, the external data bus can be either narrower or wider. The external data path is normally not as wide as the internal data path.

Having a smaller external bus (data path) will slow the performance of the-CPU, but it makes it simpler to upgrade earlier system designs to a new processor. Having a larger external data bus will improve the performance as data can be brought into the CPU in large chunks.

The Address Lines

The address lines are used to specify the exact location in memory where data can be found. The standard PC is a binary device. Using the memory address bus, CPUs send out location information on their address lines (or control lines) and these address lines are routed to every other major component of the computer (memory, ROM, expansion bus etc).

The numbers of address lines within the memory address bus will determine the maximum number of addressable locations. For example, if a PC has 3 address lines the maximum number of addressable memory locations is 8.


Whenever you are using a computer to achieve a task, the computer processor gets busy fetching, decoding and executing program instructions that are being issued to it. But remember it must work in conjunction with other computer components so as to achieve the desired goals.

You can also learn more about the CPU from this great book by Mike Meyers, CompTIA A+ Certification All-in-One Exam Guide.


For each question, choose the best answer. The answer key is below.

  1. A register is also referred to as an accumulator
    • Yes
    • No

Answer Key

  1. Yes

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: Why is the processor a key component of a computer?

Answer: This is is because it is the brain of the computer. The central processing unit performs all the processing working of the entire computer system. It fetches, decodes and executes instructions obtained from software programs, performs arithmetic calculations, and controls and supports the timing of each operation that takes place in the computer system. Without the processor, the computer will just be a junk.

© 2011 Patrick Kamau


Patrick Kamau (author) from Nairobi, Kenya on December 08, 2019:

Hello, Debra Hampton, it would be good to check the processor speed, amount of RAM and the hard disk drive capacity. This will let you know if the system units you will receive meets your specifications.

Debra Hampton on December 08, 2019:

We are going to be receiving CPU units and memory modules. Is there a test we can use to know if the units are meeting specifications? I'm a newbie in this field so be patient with me please.

Kenneth Cudjoe on October 17, 2019:

I want to see reference

Patrick Kamau (author) from Nairobi, Kenya on September 25, 2019:

Thank you, Asom for taking time to comment. All the best in your endeavors.

Asom emmanuel on September 25, 2019:

Am ok with the few I learnt.

More grace

bob stone on July 09, 2019:

what is the alu

Daniel Bandeira on June 26, 2019:

Great article! I am really satisfied by reading it!

Khushi Takodara on March 22, 2019:

It's really helpful. Thank you so much for upload it.

My question is what is the difference between processor and micro processor?

Patrick Kamau (author) from Nairobi, Kenya on October 25, 2018:

You are much welcome Sowmya. Thanks for reading and commenting. Hope you will check more of my articles.

Sowmya on October 23, 2018:

Thank you.. information is very clear and helpful

mr.v.k on September 22, 2018:

what I/O peripherals are built into the processor chip.

khan on November 24, 2017:

wow pretty good i like it.

emily on January 23, 2017:

this is very informative thanks

Patrick Kamau (author) from Nairobi, Kenya on November 26, 2014:

Thanks you TTGReviews for the compliment, I am glad you liked the information.

TTGReviews on November 18, 2014:

Nice explanation of processor information

Patrick Kamau (author) from Nairobi, Kenya on October 02, 2012:

Thanks amanda for reading and commenting, I am glad you liked it. My wish is for others to know much more about computers. Stay tuned.

amanda on October 02, 2012:

thanks for the helpful are doing a really good thing by helping others.....u have truly helped me....can keep me posted with need email is you:)

Patrick Kamau (author) from Nairobi, Kenya on August 06, 2012:

Thanks henry udeme-obong for reading and commenting. These are very useful tutorials indeed. They will teach you what you have been wanting to know about computers.

henry udeme-obong on July 21, 2012:

am so grateful for what you've been doing here Ptkey. i must tell you that you've just made me a fulfill man now. thanks so much but i will like to be following you always. my email is please just send me new post when ever it is ready please thanks so much, your really a great man indeed. keep it up

Patrick Kamau (author) from Nairobi, Kenya on March 27, 2012:

@ Roserade, thank you for reading and commenting. Your comment is encouraging and it is good that you realize there are people out there who need this kind of information. I will be grateful for your follow up. Thanks and all the best.

Roserade on March 26, 2012:

Very informative and helpful. It may be tiring to do this sometimes but it's all worth keep up the good work and don't give up...I'll be cheering for you...:)

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