What Is a CPU? (Central Processing Unit)

All about CPUs, CPU cores, clock speed, and more

The central processing unit (CPU) is the computer component that's responsible for interpreting and executing most of the commands from the computer's other hardware and software.

Types of Devices That Use CPUs

All sorts of devices use a CPU, including desktop, laptop, and tablet computers, smartphones, even your flat-screen television set.

Intel and AMD are the two most popular CPU manufacturers for desktops, laptops, and servers, while Apple, NVIDIA, and Qualcomm are big smartphone and tablet CPU makers.

You may see many different names used to describe the CPU, including processor, computer processor, microprocessor, central processor, and "the brains of the computer."

Computer monitors or hard drives are sometimes very incorrectly referred to as the CPU, but those pieces of hardware serve entirely different purposes and are in no way the same thing as the CPU.

What a CPU Looks Like and Where It's Located

An illustration of what a CPU is, including where it's located, what it looks like, and examples.
Lifewire  / Wenja Tang 

A modern CPU is usually small and square, with many short, rounded, metallic connectors on its underside. Some older CPUs have pins instead of metallic connectors.

The CPU attaches directly to a CPU "socket" (or sometimes a "slot") on the motherboard. The CPU is inserted into the socket pin-side-down, and a small lever helps to secure the processor.

After running even a short while, modern CPUs can get very hot. To help dissipate this heat, it's almost always necessary to attach a heat sink and a fan directly on top of the CPU. Typically, these come bundled with a CPU purchase.

Other more advanced cooling options are also available, including water cooling kits and phase change units.

Not all CPUs have pins on their bottom sides, but in the ones that do, the pins are easily bent. Take great care when handling, especially when you're installing them onto the motherboard.

CPU Clock Speed

The clock speed of a processor is the number of instructions it can process in any given second, measured in gigahertz (GHz).

For example, a CPU has a clock speed of 1 Hz if it can process one piece of instruction every second. Extrapolating this to a more real-world example: a CPU with a clock speed of 3.0 GHz can process 3 billion instructions each second.

CPU Cores

Some devices use a single-core processor while others may have a dual-core (or quad-core, etc.) processor. Running two processor units working side-by-side means that the CPU can simultaneously manage twice the instructions every second, drastically improving performance.

Some CPUs can virtualize two cores for every one physical core that's available, a technique known as Hyper-Threading. Virtualizing means that a CPU with only four cores can function as if it has eight, with the additional virtual CPU cores referred to as separate threads. Physical cores, though, do perform better than virtual ones.

CPU permitting, some applications can use what's called multithreading. If a thread is understood as a single piece of a computer process, then using multiple threads in a single CPU core means more instructions can be understood and processed at once. Some software can take advantage of this feature on more than one CPU core, which means that even more instructions can be processed simultaneously.

Example: Intel Core i3 vs. i5 vs. i7

For a more specific example of how some CPUs are faster than others, let's look at how Intel has developed its processors.

Just as you'd probably suspect from their naming, Intel Core i7 chips perform better than i5 chips, which perform better than i3 chips. Why one performs better or worse than others is a bit more complex but still pretty easy to understand.

Intel Core i3 processors are dual-core processors, while i5 and i7 chips are quad-core.

Turbo Boost is a feature in i5 and i7 chips that enables the processor to increase its clock speed past its base speed, like from 3.0 GHz to 3.5 GHz, whenever it needs to. Intel Core i3 chips don't have this capability. Processor models ending in "K" can be overclocked, which means this additional clock speed can be forced and utilized all the time; learn more about why you'd overclock your computer.

Hyper-Threading enables the two threads to be processed per each CPU core. This means i3 processors with Hyper-Threading support just four simultaneous threads (since they're dual-core processors). Intel Core i5 processors don't support Hyper-Threading, which means they, too, can work with four threads at the same time. i7 processors, however, do support this technology, and therefore (being quad-core) can process 8 threads at the same time.

Due to the power constraints inherent in devices that don't have a continuous supply of power (battery-powered products like smartphones, tablets, etc.), their processors—regardless if they're i3, i5, or i7—differ from desktop CPUs in that they have to find a balance between performance and power consumption.

More Information on CPUs

Neither clock speed, nor simply the number of CPU cores, is the sole factor determining whether one CPU is "better" than another. It often depends most on the type of software that runs on the computer—in other words, the applications that will be using the CPU.

One CPU may have a low clock speed but is a quad-core processor, while another has a high clock speed but is only a dual-core processor. Deciding which CPU would outperform the other, again, depends entirely on what the CPU is being used for.

For example, a CPU-demanding video editing program that functions best with several CPU cores is going to work better on a multicore processor with low clock speeds than it would on a single-core CPU with high clock speeds. Not all software, games, and so on can even take advantage of more than just one or two cores, making any more available CPU cores pretty useless.

Another component of a CPU is cache. CPU cache is like a temporary holding place for commonly used data. Instead of calling on random access memory for these items, the CPU determines what data you seem to keep using, assumes you'll want to keep using it, and stores it in the cache. Cache is faster than using RAM because it's a physical part of the processor; more cache means more space for holding such information.

Whether your computer can run a 32-bit or 64-bit operating system depends on the size of data units that the CPU can handle. More memory can be accessed at once and in larger pieces with a 64-bit processor than a 32-bit one, which is why operating systems and applications that are 64-bit-specific cannot run on a 32-bit processor.

You can see a computer's CPU details, along with other hardware information, with most free system information tools.

Beyond the standard processors available in commercial computers, quantum processors are being developed for quantum computers using the science behind quantum mechanics.

Each motherboard supports only a certain range of CPU types, so always check with your motherboard manufacturer before making a purchase.

  • How do I check the CPU temp?

    To test your computer's CPU temperature on a Windows PC, use a free or low-cost monitoring program like SpeedFan, Real Temp, or CPU Thermometer. Mac users should download System Monitor to monitor CPU temperature, processing load, and more.

  • How do I clean thermal paste off a CPU?

    Use an isopropyl wipe to gently wipe the thermal paste off your LGA socket. Be sure to wipe in a straight line. Repeat the process as necessary, using a fresh wipe with each effort.

  • How do I lower CPU usage?

    To lower CPU usage, free up space by disabling processes you don't need via the Task Manager. You can also try defragmenting your Windows PC, running only one or two programs at a time, and uninstalling programs you don't need.

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