What Is A CPU and What Does It Do? [Technology Explained]

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Although most moderately tech-savvy people today know that a CPU is one of the components in their computers, not many people know what a CPU actually does. In fact, if asked, most people probably would not know what CPU stands for.

But when searching for a new desktop or laptop, and typical CPU-related terms such as “quad-core” or ” i7 core”  pop out from advertisements, each proclaiming their superiority over the other — what is a person to do, especially if he or she has no idea what either of those terms mean?

First of all, what is a CPU?  CPU (also commonly called a microprocessor) stands for “central processing unit”. It’s a very suitable name, because it describes exactly what the CPU does: it processes instructions that it gathers from decoding the code in programs and other such files. A CPU has four primary functions: fetch, decode, execute, and writeback.

what is a cpu


In the first step, the CPU retrieves the instruction that it needs to run from program memory. Each instruction in a program (which contains millions of instructions) is stored at a specific address. The CPU has a program counter, which keeps track of the CPU’s position in the program – more specifically, the address of the instruction that the CPU is accessing.


For this step, it’s important to know that no matter what code a program is written in, the compiler for that specific language breaks the code down to Assembly Language. Assembly language is a language that the CPU understands, but may vary between different CPUs. From there on, an “˜assembler’ translates Assembly Language into binary code, which the CPU can manipulate to execute the instructions it is given.

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what is a cpu


Based on the instructions it is given, the CPU can then do one of three things:

1) Using its Arithmetic Logic Unit (ALU), the CPU can calculate extremely complicated mathematical functions;

2) Move data from one memory location to another;

3) Jump to different addresses in the program based on decisions made by the CPU itself.

The diagram above shows the setup of an extremely simple microprocessor capable of performing these actions.


Typically, each of the actions taken by the CPU produces some sort of output. The CPU takes this output and writes it into the computer’s memory. For example, if a program wanted to execute the first item of the list above on two operands, 3 and 5, the output, 8, would be written back into a specific address. However, for the 3rd bullet, the program counter (which, as stated above, is used to keep track of the CPU’s progress through a program) simply changes to reflect the start of the next set of instructions.

When these four steps have been completed, the Program Counter moves onto the next instruction and repeats the entire process again, until the termination of the program.

what is a cpu

Another important component of a CPU is called the “clock.” The clock produces a signal that acts to synchronize the logic units within the CPU as they execute the instructions given in a program. In the diagram above, the purple line represents the signal of a clock as it is being inputted into a logic unit. For every time the line goes from low to high, and back to low (one cycle), an instruction is carried out.

Thus, the CPU Clock speed refers to the number of times that a CPU’s clock cycles per second. Typical computers have a clock speed around 2.8 GHz (Gigahertz), which means that the clock cycles 2.8 billion times a second, and executes an equivalent number of instructions!

Now, even though this seems like an incredible amount of information processed, a CPU operating solely on the technology explained above would still be slow, if it were not for parallelism, and multi-core technology. But I’ll leave that for later, as I’ve just given you a great deal of information to digest. Now, you’re a little closer to learning how processors work, and to to gauging which processor is best for your needs.

In Part 2, I’ll explain more in depth about the technology that goes into dual- and quad-core technology, and what claims such as “Hyper-threading” mean. I’ll also  introduce the concept of overclocking a CPU (the practice of increasing the clock rate of a CPU to increase its performance and speed).

What CPU does your computer have? Have you ever thought about overclocking your computer? Let us know in the comments!

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Comments (14)
  • Dennis Primm

    Please forgive me… I meant to post my comment on the 7nm IBM Chip Doubles Performance, Proves Moore’s Law Through 2018.

  • Dennis Primm

    Thank you for this amazing article!!!

    When I got out of the Army I went to junior college to learn about electronics technology (my focus was on computers), we used the 6502 processor to train on and were looking forward to the Zilog Z80 coming onto the scene. We used machine code and assembler language to program the computer. That was back in the early 1980’s. A lot of time has passed since then, but if my memory serves me correctly a CPU needs to have these three (3) items or building blocks:

    1) a Program Counter,
    2) an Instruction Register, and
    3) an Arithmetic Logic Unit (ALU)

    I haven’t researched the latest CPUs and their building blocks, but those blocks were what was needed back in the old days. I would think the fundamentals are still the same today.

    If people really knew what goes on behind the scenes in their computers they would be quite amazed to know what is required to get what they are viewing on their monitors! There is quite a lot happening just to get the answer to a simple question like 1 + 1 = ? displayed on a seven segment display (like is used on a digital watch/clock) The answer of course is 2, but to arrive at that answer and display it in a seven segment display is quite an amazing process! You’ve got all of the basic logic gates (and, or, nor, exclusive or, and nand, nor, inverters, etc.) doing their thing to arrive at an answer and then once an answer is arrived at what is needed to display it is another feat. It really is quite an amazing concerted effort to perform just the basic arithmetic functions.

    I followed a link in this article about Quantum computers and that just amazes me too! I have a hard time understanding “qubits”, but I’m sure in a few years they will be discussed about and understood just like we talk about “bits” (either a 0 or 1 state) today.

    I’m so glad you have shown us what the leading edge technology is. We need to have an appreciation of what it is and what it will do for us in the future.

    Thanks again for your article!

  • eitrige

    very interesting article, thank you!

  • sankar

    then go to school daily, definitely u’ll get it one day.

    • kevin

      Its kinda hard to learn at school cuz right now I don’t have the money to go to school every day


    Woooooooow!! i’ve learn’t alot from u people.thanx alot. but each and every function of the 4 primary functions takes place in different components of a CPU right? And if yes, then i would please luv to know the parts respectively.

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Affiliate Disclamer

This review may contain affiliate links, which pays us a small compensation if you do decide to make a purchase based on our recommendation. Our judgement is in no way biased, and our recommendations are always based on the merits of the items.

For more details, please read our disclosure.
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