Technology Explained

What Is A CPU and What Does It Do?

James Frew 11-12-2019

Acronyms are the tech world’s favorite way to make interesting technology sound incredibly confusing. When hunting out a new PC or Laptop, the specifications will mention the type of CPU you can expect to find in the shiny new device. Frustratingly, they almost always fail to tell you why that’s so important.


When faced with decisions between AMD and Intel, dual or quad-core, and i3 vs. i7 or i5 vs. i9, it can be hard to tell what the difference is and why it matters. Knowing which is best for you can be difficult, but we’re here to help you out.

What Is A CPU?

The Core Processing Unit (CPU) is often referred to as the brains of the computer. While the CPU only makes up one of many processing units, it is one of the most important. It is the part of a computer that performs calculations, actions, and runs programs.

What Is A CPU and What Does It Do? CPU Shutterstock

The CPU takes instructional inputs from the computer’s RAM, decodes and processes the action, before delivering an output. CPUs are in all sorts of devices ranging from computers and laptops, to smartphones, tablets, and smart TVs. The small and usually square chip is placed onto the device’s motherboard and interacts with the other hardware to operate your computer. If you want to dig a little deeper into computer mechanics, then a great place to start is J. Clark Scott’s book But How Do It Know? (UK).

How Do They Work?

There have been a lot of improvements over the years since the first CPUs came on the scene. Despite that, the basic function of the CPU has remained the same consisting of three steps; fetch, decode, and execute.



Just as you may expect, fetching involves receiving an instruction. The instruction is represented as a series of numbers and is passed to the CPU from the RAM. Each instruction is only one small part of any operation, so the CPU needs to know which instruction comes next. The current instruction address is held by a program counter (PC). The PC and instructions are then placed into an Instruction Register (IR). The PC length is then increased to reference the next instruction’s address.


Once an instruction is fetched and stored in the IR, the CPU passes the instruction to a circuit called the instruction decoder. This converts the instruction into signals to be passed through to other parts of the CPU for action.


In the final step, the decoded instructions are sent to the relevant parts of the CPU to be completed. The results are usually written to a CPU register, where they can be referenced by later instructions. Think of it like the memory function on your calculator.

How Many Cores?

In the early days of computing a CPU would only have a single core What Is A Processor Core? [MakeUseOf Explains] Every computer has a processor, whether it's a small efficiency pro or a large performance powerhouse, or else it wouldn't be able to function. Of course, the processor, also called the CPU or Central Processing... Read More . This meant that the CPU was limited to just a single set of tasks. This is one of the reasons that computing was often a relatively slow and time consuming, but world changing A Brief History of Computers That Changed the World You can spend years delving into the history of the computer. There are tons of inventions, tons of books about them – and that’s before you start getting into the finger-pointing that inevitably occurs when... Read More affair. After pushing the single-core CPU to its limits, manufacturers started looking for new ways to improve performance. This drive for performance improvements led to the creation of multi-core processors. These days it’s likely that you will hear terms thrown around like dual, quad, or even octo-core.


A dual-core processor for example is really just two separate CPUs on a single chip. By increasing the amount of cores, CPUs were able to handle multiple processes simultaneously. This had the desired effect of increasing performance and reducing processing time. Dual-core soon gave way to quad-core processors with four CPUs, and even octo-core processors with eight. Add in hyper-threading What Is Hyper-Threading? [Technology Explained] Read More  and your computer can perform tasks as if they had up to 16 cores.

Understanding The Specs

Having a knowledge of the operation of a CPU alongside the differing brands and core numbers is helpful. However, there are a lot of options out there even with the same high-level specifications. There are some other specs that can help you decide between CPUs when it comes to time to buy.

Mobile vs. Desktop

Traditionally computers were large static electronic devices powered by a constant supply of electricity. However, the shift to mobile and the rise of the smartphone has meant that we essentially carry a computer with us everywhere we go. Mobile processors are optimized for efficiency and power consumption so the device’s battery lasts as long as possible.

What Is A CPU and What Does It Do? MultiDevice Shutterstock


In their wisdom, manufacturers have taken to naming both their mobile and desktop processors the same thing but with a range of prefixes. This is despite them being different products. Mobile processor prefixes have “U” for ultra-low power, “HQ” for high performance graphics, and “HK” for high performance graphics with the ability to overclock. Desktop prefixes include “K” for ability to overclock,and “T” for optimized power.

32 or 64-bit

A processor doesn’t receive a constant flow of data. Instead it receives the data in smaller chunks known as a “word.” The processor is limited by the amount of bits in a word. When 32-bit processors were first designed, it seemed like an incredibly large word size. Moore’s Law continued to hold, however, and suddenly computers could handle more than 4GB of RAM — leaving the door open for a new 64-bit processor What Is 64-bit Computing? The packaging of a computer or computer hardware is crowded with technical terms and badges. One of the more prominent ones is 64-bit. Read More .

Thermal Power Design

The Thermal Power Design is a measure of maximum power in Watts your CPU will consume. While a lower power consumption is clearly good for your electricity bills it can have another surprising benefit — less heat.

CPU Socket Type

In order to make up a fully-functioning computer, the CPU needs to be attached to the other components through the motherboard. When choosing a CPU you need to ensure that the CPU and motherboard socket types match CPU Socket Types Explained: Socket 5 to BGA Computer CPUs have a home: the socket. If you plan to upgrade, you need to understand how the CPU connects to your motherboard. Read More .


L2/L3 Cache

The L2 and L3 cache is a speedy, on-board memory for the CPU to use during processing. The more you have of it, the faster your CPU will perform 5 Little-Known Specs That Could Be Slowing Down Your PC We'll take a look at five lesser known factors that affect your computer's performance, and show you how you can always get maximum bang for your buck when upgrading. Read More .


The frequency refers to the operating speed of the processor. Before multi-core processors, frequency was the most important performance metric between different CPUs. Despite the addition of features, it is still an important specification to take into account. It is possible for a very fast dual-core CPU to outperform a slower quad-core CPU for example.

The Brains of the Operation

The CPU really is the brain of the computer. It performs all the tasks that we would typically associate with computing. Most of the other computer components are really there to support the operation of the CPU. The improvements made in processor technology including hyper-threading and multiple cores played a key part in the Technical Revolution.

Being able to differentiate between an Intel i7 dual-core and an AMD X4 860K quad-core will make decision time that much easier. That’s not to mention potentially saving you money on overpowered hardware. However, despite their importance, there are many other ways to upgrade your PC too Which Upgrades Will Improve Your PC Performance the Most? Need a faster computer but aren't sure what you should upgrade on your PC? Follow our PC upgrade checklist to find out. Read More .

How much did you know about CPUs? What CPU does your computer have? Has this inspired you to upgrade? Let us know in the comments below!

Image Credit: Vania Zhukevych via

Related topics: Computer Parts, Computer Processor, CPU.

Affiliate Disclosure: By buying the products we recommend, you help keep the site alive. Read more.

Whatsapp Pinterest

Leave a Reply

Your email address will not be published. Required fields are marked *

  1. thelazypanda
    April 23, 2020 at 10:47 am

    Good articles very helpful in understanding the technical jargon. Good work.

  2. Safiqul Islam
    January 16, 2018 at 5:43 pm

    I had some basic concepts regarding CPU .But my experience was not so enriched as your article exposes & clarifies.I have been using an android device which is quadcore, viz, it has 4 processors in njmbers.The processor is built by mediatech in the scale of 28nm gate.Presently only 1 processor is working in my mobile & the remaining 3 are stopped. Its frequency is of 1.44GHZ inbuilt.Frequency is fluctuating based on network.In my opinion among the hardware processor is the most valuable part like brain of human being.However, as it is induced with some basic feature its capabilities are limited. In this age of technology it has immense role.It has undervalued the use of computer.
    The world famous processors are: intel, amd, snapdragon qualcom,exynos, mediatech,navidia & so on.
    Now octacore has made its access in the market.

  3. Abdullah Tashtoush
    September 25, 2017 at 6:04 pm

    I 'D LIKE TO ASK ABOUT THE relation between the size of transistor and the clock speed?
    and which is related to the same question: why the clock speed saturated and rising up with transistor's size?

    • James Frew
      September 26, 2017 at 5:50 am

      As far as I know it has no direct relation, although happy to be corrected on that.