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What is a CPU? A beginner’s guide to processors

What is a CPU?

The CPU, Central Processing Unit, or simply processor, is the main chip in a computer responsible for carrying out all tasks. It’s responsible for telling all the other components in a computer what to do, according to the instructions it is given by the programs (software) running on that computer.

In fact, CPUs exist in many kinds of device apart from computers. If something can run programs, chances are it will have a CPU. For example, phones and TVs have CPUs inside them.

In modern computers, and especially in smartphones, the CPU may sit on the same physical chip as other components. Most modern computer CPUs share a chip with a computer’s graphics electronics (that decides what appears on your monitor). An example of this is the Intel Core i7-7700K.

In smartphones and tablets the chip containing the CPU may also handle phone calls, Wi-Fi, GPS and many other things. Such multi-purpose chips are known as SoCs (system-on-a-chip). An example of this would be the Qualcomm Snapdragon 835.

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Snapdragon 810Mobile SoCs contain a CPU and loads of other important kit that makes your phone work

Where is the CPU?

In a computer, the CPU is found at the heart of the system, plugged into the motherboard. You wouldn’t be able to see it if you took the side panel off your desktop PC, as it will be hidden under a cooling fan – a CPU is a powerful component and would get very hot without proper cooling.

In a desktop PC, the CPU and cooler are designed to be easy to remove. This means replacing the chip if it goes wrong is a simple process. It doesn’t mean a processor can be easily swapped for a more powerful model, however, as the CPU will need to be compatible with the motherboard.

Most of the time, if you’re upgrading to a CPU that’s a year or two newer than your current one, you’ll also need to fit a new motherboard.

In laptops, on the other hand, the CPU and cooler are as good as impossible to remove (and even harder to replace). It’s also not possible to change the motherboard, so it’s best to think as laptops as non-upgradable in this regard.

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 Best CPU coolersSome examples of CPU coolers

CPU Jargon Buster: Speed

There is a vast difference in computing performance between different models of CPU. PC and laptop manufacturers tend to splash three things all over their marketing material when trying to sell you a computer: CPU model (see below), clock speed and number of cores.

Clock speed is expressed in gigahertz, or GHz, and is a rough indication of how many calculations a processor can make each second – the higher the number, the more calculations.

CPU Jargon Buster: Cores

How quickly a CPU can process data is also affected by how many cores it has. Each core is essentially a CPU in itself, and many programs are written so that multiple cores can work on processing the data the program requires at the same time – vastly increasing how quickly that program can run.

Modern CPUs have at least two cores, with many having four, eight or even more. Having multiple cores will certainly give you a speed boost, but it depends on the kind of program you’re running: a quad-core processor can perform some tasks, such as video editing, almost twice as fast as a dual-core chip, but this won’t be the case in all situations.

For more, read our Intel Core i3, i5 and i7 guide, which explains how cores can make a difference in more detail.

CPU Jargon Buster:  Model names

There are two main CPU manufacturers in the computer industry: AMD and Intel. Both companies make many different CPUs under many different model names, but those names, such as Core M or Atom, don’t tell you a great deal about a CPU’s capabilities. Here’s a quick breakdown to give you an idea of what each CPU range can do.

What else should I know about laptop CPUs?

Almost all laptops have Intel CPUs. The ranges are:

  • Atom: Power-efficient but not-very-fast chips for smartphones, tablets and small cheap laptops. Devices with these CPUs tend to struggle to run Windows smoothly, but have great battery life.
  • Core M: Another range of power-efficient chips, but far faster than anything with an Atom logo. Good for light laptops with long battery life.
  • Core i3/i5/i7: Intel’s main laptop CPUs. Broadly speaking, the i7 CPUs are the fastest, i3 are the slowest and i5 sit in the middle. It’s a little more complicated than that in reality, which is why we’ve written the handy guide we mentioned above. Intel rival AMD makes chips called A4 up to A10, which are roughly equivalent.

What else should I know about desktop CPUs?

Intel has some real competition when it comes to desktop PCs, with the latest AMD Ryzen CPUs promising serious power at a good price.

As with laptops, desktop processor ranges are complicated. The main thing to remember is that, despite differences in design, Intel and AMD CPUs offer broadly similar performance for the price.

This means that if you buy a £500 AMD PC, it will be around as quick as a £500 Intel PC. Enthusiasts buying absolutely state-of-the-art kit will want to dig a little deeper, but most people will be happy with a PC containing a CPU from either manufacturer.

Related: Best desktop PC

Got any questions about CPUs? Ask away in the comments below – we’re here to help!

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