If you're wondering whether you need a Core i3, i5 or i7 processor for your next upgrade or brand new PC, then take a seat and we'll explain the differences to help you make the correct choice

The general rule is that as you move up from the i3 to the i5 and then the i7, the more power (and more expensive) the processors get.

These days, even a basic dual-core processor is fast enough for undemanding tasks. This means that whether you're buying a laptop or a PC, Windows should run perfectly well on even a budget model.

Undemanding tasks are just about everything that doesn't include gaming and video editing (If you do want to do these, see our guide to the best processor for gaming and video editing).

Essentially, if you just want to do all the normal things people do with their computers - email, web browsing, YouTube, editing and sharing photos, Microsoft Office - a basic processor is fine.

If you're reading this during the process of trying to choose a budget laptop, know that one of the most influential components for overall responsiveness is the hard drive. It's worth sacrificing a Core i5 processor for an i3 if you can get an SSD instead of a traditional hard disk for the same sort of price.

Check out our list of the best cheap laptops and buying advice, too.

How many cores do I need?

You rarely, if ever, see single-core processors any more and you should avoid these at all costs. More cores means more performance, plus the ability to run multiple applications at the same time.

Many programs can also take advantage of multiple cores so even if you're only running that one program, you should see an improvement in its performance compared with running it on a computer whose CPU has fewer cores.

Hyper-Threading

Don't just look at the number of cores, though. Intel processors often support Hyper-threading which effectively allows it to handle twice the number of 'threads' and is a bit like having double the number of cores, albeit virtually. 

A thread in computing terms is a sequence of programmed instructions that the CPU has to process. If a CPU has one core, it can process only one thread at once, so can only do one thing at once. It's actually more complex than this, but the aim here is to keep it simple and understandable.

Hence, a dual-core CPU can process two threads at once, a quad-core four threads at once. That's twice or four times the work in the same amount of time.

Hyper-Threading is a clever way to let a single core handle multiple threads.

A Core i3 with Hyper-Threading can process two threads per core which means a total of four threads can run simultaneously. The current Core i5 range of desktop processors doesn't have Hyper-Threading so can also only process four cores. i7 processors do have it, so can process eight threads at once. Combine that with 8MB of cache and Turbo Boost (below), and you can see why Core i7 chips are more powerful than an i5 or i3.

Turbo Boost

Turbo Boost is Intel's marketing name for the technology that allows a processor to increase its core clock speed whenever the need arises. The maximum amount that Turbo Boost can raise clock speed depends on the number of active cores, the estimated current consumption, the estimated power consumption, and the processor temperature.

Core i3 processors don't have Turbo Boost, but i5 and i7s do. It means that Core i3 chips tend to have quite high 'base' clock speeds.

If a processor model ends with a K, it means it is unlocked and can be 'overclocked'. This means you can force the CPU to run at a higher speed than its base speed all the time for better performance.

A dual-core processor running at a faster speed than a quad-core processor could have similar performance overall.

8th generation Intel Core processors

The current range of 8th generation Intel Core processors for desktops is pretty vast, with several different processors for each i3, i5, and i7 category. These have the codename Coffee Lake.

The most powerful being the 8700k which is the top of the pile for the i7. This processor holds 6 cores / 12 threads, a base clock speed of 3.7 GHz with a Max Turbo frequency of 4.7 GHz, and 12MB of cache.

The least powerful being the i3-8100, which holds 4 cores / 4 threads, with a base frequency of 3.6 GHz (sadly no turbo boost) and 6MB of cache.

The price of these varies between roughly £90 / $120 for the lower i3 processors, up to £300 / $350 for the meatier i7 versions.

You'll find some examples of the processors below.

Model: i7-8700K i5-8600K i3-8350k
Cores: 6 / 12 6 / 6 4 / 4
Base Freq: 3.7 3.6 4.0
Turbo Freq: 4.7 4.3 N/A
Cache: 12MB 9MB 8MB
TDP: 95W 95W 91W
Price: £295 / $359 £220 / $260 £140 / $170


What about graphics?

Many Intel processors have a GPU - the graphics chip - built into the CPU.

These graphics are good enough for everyday tasks, but if you're planning on doing any gaming or video editing, then you'll want to investigate a stand alone graphics card for your system too.

What is an i9?

There is a more powerful series of processor available, which is the Intel Core i9.

These aren't really aimed at consumers, and while you can put them into your PC (assuming your motherboard can take it) they are usually reserved for software that requires much more excessive processing power, such as running a server.

Which is best: i3, i5 or i7?

You'd be forgiven for being confused at this point. It's not possible to look at a processor's specifications and make a decision about which is fast enough for you. 

That's why we rigorously benchmark every laptop and PC we review. This tests the whole-system performance, not just the CPU. It's the processor, plus the memory (RAM) and hard drive - along with the graphics card, too - which determines how quick a PC or laptop is.

So it's crucial to read reviews before you buy one. Here are the best laptops you can buy right now and also the best PCs.

There are other factors besides performance, such as amount of power a processor uses. Newer processors are generally always more power efficient, which is important in laptops.

You either get more battery life for the same performance, or more performance for the same battery life.

But to answer the question, a top-of-the-range Core i5 is going to offer the best performance than any Core i3, but a top-of-the-range Core i3 could be enough for you compared to the slowest Core i5 from the same generation.

Similarly, if you're going to be running very demanding software such as video editing or encoding programs, then you may want to go for a Core i7. But for most people, this is overkill.

If you're after the best battery life, look for a processor with a model number ending in U, or with a Y in it. These use the least power, but also deliver slower performance.

Finally, don't forget AMD. It's new range of Ryzen processors for PCs are excellent value and the Ryzen 5 chips are better value than Intel's Core i5.