What is a CPU? How Does it Work? Everything You Need to Know

Last updated on September 13th, 2023 at 02:45 am

If you’re looking to learn more about PCs, it makes the most sense to start with the CPU. I’m sure you’ve already heard plenty about this modest chip, but what exactly is a CPU? And how does it work? 

A CPU (Central Processing Unit) is the brain of a PC. It carries out most of a computer’s processes, organizes and controls the flow of data, and tells the other components what to do. The CPU’s fundamental workflow can be represented by the fetch-execute cycle. 

In this article, I’ll tell you everything you need to know about what a CPU is and how it works. I’ll also tell you what to look out for in a CPU when choosing one for your PC. Stick around if that interests you!

What a CPU is

The Central Processing Unit is a tiny rectangular chip (usually only a few centimeters in length and width and a few millimeters in height) that rests in its dedicated socket on the motherboard and effectively acts as the brain of the entire PC. 

The CPU fulfills most of the processing needs of a PC. So, executing instructions, opening files, running programs, issuing commands, running calculations, and much more – it’s all done by this tiny chip.  

The CPU also controls all the other components in a system, such as the RAM (Random Access Memory), Storage devices (SSD or HDD), and GPU (Graphics Processing Unit). 

It issues commands to these components and, in lay terms, tells them what to do. 

When you launch an app, it’s your CPU that extracts data from storage and loads it into memory. When you’re playing a game, it’s your CPU that continuously instructs the GPU to process and generate the frames you’re shown on screen. 

The CPU is arguably the most important component of a modern PC, second to the GPU only in PC builds designed with an emphasis on gaming performance. 

How a CPU Works

A CPU is a brilliant piece of electronic machinery. It may very well be humanity’s most important invention to date. 

The way a CPU works is quite simple when you break it down into steps. We can break down the CPU’s processing into a fetch-execute cycle. Essentially, the CPU:

• Fetches an instruction from the system’s main memory and holds it in a local register. 
• Decodes the instruction to make sense of it. 
• Executes the instruction. 
• Fetches the next instruction – the cycle repeats. 

Instructions are dealt with one at a time in this way. 

Now, we know that PCs can multitask with ease. You can run multiple apps at the same time without any lag or delay. Well, how come?

It boils down to the fact that the CPU can fetch and execute billions of these instructions per second. So, even though, technically, a single CPU core is never really ‘multitasking,’ its tremendous processing speed makes it seem so.  

Additionally, modern CPUs have multiple microprocessors, so they can complete tasks in parallel. 

4 Things to Consider Before Choosing a CPU for Your PC

How do we compare CPUs? What makes one superior to another? 

Let’s talk about some performance-determining metrics to help you determine which CPU is right for you. 

1. Clock Speed

You can think of clock speed as the frequency with which a CPU chip completes fetch execute cycles. In other words, the number of instructions the CPU can execute in a second. 

As I mentioned earlier, modern CPUs can execute billions of these instructions per second. Today, even entry-level processors feature clock speeds of over 3 GHz (3 billion clock cycles per second). 

Mid to high-end processors can easily break 4 GHz, with the best processors even topping 5 GHz speeds. 

Fun fact: The world record for the fastest CPU frequency is held by the Intel Core i9 13900K, at an astounding 9.008 GHz. 

Lower clock speeds will be more than sufficient for browsing, office work, or casual gaming. However, having a CPU with high clock speeds is essential if you intend to play any of the recent triple-A titles at a stable 60 fps or more. 

Check out: What’s the meaning of Ghz? To go more in-depth on this topic.

2. Cores and Threads

Modern CPU chips have multiple microprocessors built into them. They’re referred to as cores. Each of these microprocessors can execute instructions individually, allowing for more efficient multitasking and increasing the overall processing speed of the chip. 

Desktop CPUs will usually have at least 4 cores. 

Hyperthreading allows each of these CPU cores to handle two threads (do two tasks) in parallel, speeding up the process even further. 

So, for example, a 4-core CPU with hyperthreading enabled will be able to tackle 8 tasks at once. Keep in mind that this is still not as good as having an 8-core CPU, though. 

Now, you may be wondering: How important is core/thread count for gaming?

It matters, but not as much as you’d think. Many modern-day games can’t make use of numerous threads very efficiently. Clock speed matters much more than core/thread count for gaming. 

Having a high core/thread count provides the most benefits for tasks that can be broken up into multiple parts and run in parallel – video editing, for example. 

If you want to learn more check out: “Higher Clock Speed or More Cores When Gaming.”

3. Power Draw

Power draw is not a major concern since CPUs are quite modest. Compared to GPUs, at least, which are usually by far the most power-hungry component in a PC. 

Still, you want to be sure you don’t end up with a CPU your power supply unit can’t handle. Your average CPU chip will consume 60 to 100 watts of power. 

The newer generations of CPUs from both Intel and AMD are monsters, though. They feature never-seen-before clock speeds and thread counts, but it comes at the expense of power consumption. You may be looking at upwards of 150 to 200 watts of power being designated to the CPU alone. 

You can find out the power draw for any particular CPU from the manufacturer’s website. 

4. Compatibility

CPU chips differ slightly in their dimensions. They’re designed to fit into a particular socket. This determines their compatibility with motherboards. 

When getting a new CPU, you should ensure you have a compatible motherboard first. 

Additionally, while newer CPUs can support the lightning-fast DDR5 memory, older CPUs will only be able to support DDR4 and DDR3 memory sticks. 

Find out how much of a difference RAM speed makes. 

Final Thoughts

A CPU is one of the electronic components inside a computer. It carries out almost all of the processing and delegates specialized tasks to other components. 

It carries out processes through the fetch-execute cycle, where each instruction is fetched from memory, decoded, and executed, one after another. 

When choosing a PC, the primary feature