What Does CPU Stand For, and What Does a Processor Do?

By David NaarLast Updated Mar 16, 2021 4:50:55 PM ET
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You've probably heard of a computer CPU, but what exactly is it, and what does it do? CPU stands for "central processing unit," and it's an essential piece of hardware that enables a computer to work.

A computer’s CPU may occasionally be referred to as the "central processor" or just a "processor," but these terms generally all describe the same component. To learn more about the basics of computer hardware, it’s important to learn more about the main functions of a computer CPU and explore different types of processors for various devices to see these functions in action.

Why Is a CPU Important?

When it comes to a computer CPU's overall function, it can be helpful to think of this component as the computer’s "brain." The CPU controls a computer's operations and enables it to carry out the instructions and commands that a user inputs into the computer via its peripheral devices (like its keyboard and mouse). Without its CPU, a computer would be about as useful as a car without an engine.

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While a CPU or processor is a piece of hardware, it's a complex one that consists of several different parts. To help make this intricate piece of circuitry a bit more manageable to understand, think of it like a team of people who all work together inside a computer to perform different projects or operations — sort of a tiny factory carrying out multiple functions at the same time, all driven by electricity. When it's time for a CPU to perform, it goes to work by carrying out four essential functions.

The 4 Main Functions of a CPU

The first thing a CPU does is fetch instructions for a given task from the program memory. Going back to the team metaphor for a moment, imagine the program memory as a large library. The first member of the CPU team is an expert librarian who can instantly retrieve — or fetch — a set of instructions for any given task.

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Once the instructions are fetched, the CPU "team" now has to make sense of them. That's where two components called the instruction decoder and instruction set architecture (ISA) come in. The ISA determines how the instructions should be interpreted, and the instruction decoder translates them in a way that other members of the CPU "team" can understand.

Together, these functions produce what are known as assembly instructions in binary code. These are sort of like a CPU's version — made up of numbers — of the type of guide you might use when you attempt to construct a piece of flat-packed furniture. The instructions specify what operation the computer needs to perform, and they include the information required to do it.

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After all the instructions are in place, it's time to execute the operation in either a single action or a sequence of steps. At this point, various CPU components communicate through an electric connection to follow the directions and complete the command. As this occurs, the components make records of the project's execution. After the operation is complete, the CPU "management team" gives feedback, and the data is stored in the computer’s memory for quick access.

Different Types of CPUs

Intel and Advanced Micro Devices (AMD) are the two most popular CPU producers on the market in terms of manufacturers. Intel produces desktop CPUs like Celeron, Pentium and Core, while AMD's processors include Sempron, Athlon and Phenom.

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You may have also heard of the term "cores" used when referring to different processors. The number of cores is an important piece of information you'll want to consider when buying a computer. Using the previous CPU team analogy, think of cores as different teams within a CPU. These teams may work together or separately, but the idea is that the more you have, the faster and more efficiently your device will work.

If a CPU has two cores, it's referred to as a "dual-core processor." A processor with four cores is called a "quad-core," one with six a "hexa-core" and one with eight an "octa-core." Modern CPUs may have anywhere from two to over 100 cores, but most average computers have somewhere between four and eight.

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What Are the Key Differences in Desktop vs. Laptop CPUs?

Due to the different builds of desktop and laptop computers, laptops tend to run on less powerful CPUs largely because of heat tolerance. Desktops aren't designed with portability in mind, so they have a little more room on the inside for large, built-in cooling fans. Given that these have the power to keep a CPU from overheating, the average desktop CPU may contain as many as eight cores.

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The inside of a laptop, on the other hand, is more cramped. Because a laptop needs to remain small and light enough for a user to carry around, there's not as much room for numerous fans to keep a CPU with a large number of cores from overheating. That said, laptops that are specifically designed for gaming or programming will likely have more cores than those designed for everyday use.

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Some gaming laptops now have as many as 12 cores, which is pretty impressive. On the other hand, there are now desktop processors that contain as many as 128 cores. In general, even if a laptop's CPU has the same number of cores as a desktop's, it's still not going to be quite as powerful. Aside from heating issues, this is also because a laptop is designed to run on battery power, whereas a desktop is usually plugged into a direct energy source. Consequently, a desktop is able to run a processor that requires a great deal more energy than a laptop.