The CPU is perhaps the most well-known piece of computer hardware in the world, though not always for the right reasons. It's not uncommon to hear people call the whole computer or even something like a router a "CPU." In fact, a single CPU can fit in the palm of your hand, and it's arguably the single most important component in any computer. Here's everything you need to know about CPUs.

The brain of the computer

Put simply, the Central Processing Unit (or CPU) is the brain of the computer, the component that does the actual thinking. In order to do that thinking, CPUs are composed of one or more cores that can each accomplish workloads. CPUs also require access to memory where data can be stored, and the faster that memory, the faster tasks can be completed. Ideally, a CPU gets its data from the RAM (which is decently fast and can store a great amount of data) or from its cache (which is part of the CPU and is fast, but stores only a little data) rather than a HDD or SSD.

Like virtually all other types of processors, CPUs can come in different varieties known as instruction-set architectures (or ISAs), which is the most fundamental component of a CPU. The differences between two distinct ISAs are often so extreme that software that runs on one ISA probably doesn't run on another. Even CPUs that use the same ISA might use a different microarchitecture, another way that CPUs are designed, though not as fundamental as the ISA. Different microarchitectures offer different levels of performance, efficiency, and features.

Here's what makes the CPU unique: it's very good at accomplishing tasks in a serial, sequential order, as opposed to doing many things in parallel, or at the same time. This is why the first CPUs came with just a single core, and even two decades after the debut of the first dual-core CPU, most consumer chips offer eight cores or less, though big server CPUs usually offer anywhere from 32 to 128 cores. CPU designers are focused on delivering improvements to per-core performance by increasing clock speed or frequency (the amount of work or instructions completed per second) and instructions per clock, which depends on the microarchitecture.

The landscape of CPUs and the companies who design them

While there are many CPU designers in the world, I'm only going to focus on the biggest and most important ones; many CPU making companies make chips for electronics like calculators and industrial machines, which aren't exactly super interesting. When it comes to PCs, phones, and data centers, there are surprisingly few players.

The major companies today are Intel, AMD, Arm, and RISC-V International. You all know Intel: it's one of the oldest computer companies on the planet. Intel invented the x86 ISA, which it shares with AMD, and the two companies have been in competition since the 90s. Then there's Arm, which maintains the ARM ISA and licenses it out to other companies like Apple, Samsung, and Qualcomm, which create custom ARM CPUs with better performance compared to Arm's regular ARM cores. RISC-V International by contrast allows anyone to use and modify its RISC-V ISA, which is open-standard.

Intel and AMD, despite being the oldest of these companies, are also among the most limited and only make CPUs for PCs and data centers. Intel at one point was involved in the phone market, but eventually gave up on its plans to take over smartphones. Arm and its partners have their hands in pretty much everything by contrast. Phones and smartphones have been the traditional stronghold for ARM CPUs, but companies like Amazon and Google are introducing ARM to the data center, and Apple and Qualcomm are even taking the fight to Intel and AMD in PCs.

RISC-V however has barely any presence in this crucial markets, and instead has been gaining ground primarily in industrial applications. Still, RISC-V International and its partners have plans for taking the ISA to PCs, smartphones, and data centers to compete with Intel, AMD, and Arm. In the coming years, we'll see whether RISC-V is going to seriously disrupt the status quo, which hasn't been disturbed for many years.

What CPUs mean for your device's performance

The CPU is one of the most important components in devices like PCs and smartphones, whether it's about gaming, productivity, or doing casual stuff like browsing the internet or watching videos. There are many, many different CPUs out there with differing combinations of microarchitectures, core counts, and other features, so it's impossible to give a complete overview of what to look out for on a spec sheet. If you're the average user and you're looking to buy a great CPU, I've got some tips for you.

One of the most important things to understand is that having more cores doesn't always mean more performance. Not all applications will make use of every core, and the applications that do use lots of cores tend to be for content creation, like for rendering videos or creating 3D models. It's not a bad idea to get a modern CPU with lots of cores, but you can often find a better deal by opting for something with slightly fewer cores unless you know you need every core possible.

Gaming especially is a tricky workload for CPUs, because high clocks speeds and lots of cache are the most important features in a great gaming CPU. However, even a low-end CPU might perform identically to a high-end CPU if you choose graphics settings that set the framerate lower. For example, one CPU might only be capable of 90 FPS in a game like Star Wars Jedi: Survivor while another can do 120 FPS, but if you're playing at 60 FPS, both CPUs will be equally capable. If you're fine with the classic 60 FPS, even cheap CPUs will do the job.

Finally, if you want to get the best idea for how a CPU will perform, you're going to have to read some reviews, and this applies to desktops, laptops, and smartphones. You will have to sift through lots of graphs and tables full of numbers, but this is how you figure out what CPU is best for what. A spec sheet will never tell you the full story, and you should never just accept marketing at face value. And don't worry too much about trying to get the perfect CPU. Odds are, most chips will work fine for whatever you're trying to do.