What Is A Processor Core? [MakeUseOf Explains]

Every computer has a processor, whether it’s a small efficiency processor 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 Unit, is an important part of a functioning system, but it isn’t the only one.

Today’s processors are almost all at least dual-core, meaning that the entire processor itself contains two separate cores with which it can process information. But what are processor cores, and what exactly do they do?

What Are Cores?

A processor core is a processing unit which reads in instructions to perform specific actions. Instructions are chained together so that, when run in real time, they make up your computer experience. Literally everything you do on your computer has to be processed by your processor. Whenever you open a folder, that requires your processor. When you type into a word document, that also requires your processor. Things like drawing the desktop environment, the windows, and game graphics are the job of your graphics card — which contains hundreds of processors to quickly work on data simultaneously — but to some extent they still require your processor as well.

How They Work

The designs of processors are extremely complex and vary widely between companies and even models. Their architectures — currently “Ivy Bridge” for Intel and “Piledriver” for AMD — are constantly being improved to pack in the most amount of performance in the least amount of space and energy consumption. But despite all the architectural differences, processors go through four main steps whenever they process instructions: fetch, decode, execute, and writeback.


The fetch step is what you expect it to be. Here, the processor core retrieves instructions that are waiting for it, usually from some sort of memory. This could include RAM, but in modern processor cores, the instructions are usually already waiting for the core inside the processor cache. The processor has an area called the program counter which essentially acts as a bookmark, letting the processor know where the last instruction ended and the next one begins.


Once it has fetched the immediate instruction, it goes on to decode it. Instructions often involve multiple areas of the processor core — such as arithmetic — and the processor core needs to figure this out. Each part has something called an opcode which tells the processor core what should be done with the information that follows it. Once the processor core has figured this all out, the different areas of the core itself can get to work.

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The execute step is where the processor knows what it needs to do, and actually goes ahead and does it. What exactly happens here varies greatly depending on which areas of the processor core are being used and what information is put in. As an example, the processor can do arithmetic inside the ALU, or Arithmetic Logic Unit. This unit can connect to different inputs and outputs to crunch numbers and get the desired result. The circuitry inside the ALU does all the magic, and it’s quite complex to explain, so I’ll leave that for your own research if you’re interested.


The final step, called writeback, simple places the result of what’s been worked on back into memory. Where exactly the output goes depends on the needs of the running application, but it often stays in processor registers for quick access as the following instructions often use it. From there, it’ll get taken care of until parts of that output need to be processed once again, which can mean that it goes into the RAM.

It’s Just One Cycle

This entire process is called an instruction cycle. These instruction cycles happen ridiculously fast, especially now that we have powerful processors with high frequencies. Additionally, our entire CPU with its multiple cores does this on every core, so data can be crunched roughly as many times faster as your CPU has cores than if it were stuck with only one core of similar performance. CPUs also have optimized instruction sets hardwired into the circuitry which can speed up familiar instructions sent to them. A popular example is SSE.


Don’t forget that this is a very simple description of what processors to — in reality they are far more complex and do a lot more than we realize. The current trend is that processor manufacturers are trying to make their chips as efficient as possible, and that includes shrinking the transistors. Ivy Bridge‘s transistors are a mere 22nm, and there’s still a bit to go before researchers encounter a physical limit. Imagine all this processing occurring in such a small space. We’ll see how processors improve once we get that far.

Where do you think processors will go next? When do you expect to see quantum processors, especially in personal markets? Let us know in the comments!

Image Credits: Olivander, Bernat Gallemí, Dominik Bartsch, Ioan Sameli, National Nuclear Security Administration

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