Processors for most mobile devices run at a slower speed than a processor in a desktop PC

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Intel's first Core processors made their debut in 2006. At this point, children born in the same year are almost old enough to drink. Over a half-dozen generations of Intel Core i3, Core i5, and Core i7 CPUs have come and gone since then but most consumers are still asking the same kinds of questions.

Intel Core i3, Core i5 or Core i7? What's the difference? Is it worth it to own a CPU with more cores, a faster clock-speed or advanced features like hyper-threading?

Unless you're looking to embrace AMD’s new Ryzen processors (Looking to learn which CPU is best: Intel Core i7 or AMD Ryzen? Check out our full feature here), you’re almost certainly going to have to make the choice between Intel's three families of consumer-grade processors. 

In the past, we’re analysed what the difference between an Intel Core i3, i5 and i7 CPU was for things like Intel's 7th gen. Kaby Lake processors and whether Google’s mesh node Wi-Fi system lives up to the hype. But with the advent of Intel’s new Coffee Lake, Ice Lake and Whiskey Lake CPUs, there’s a whole new generation of PC buyers facing the same familiar decisions.

No matter who you are, you’ll want to know whether an Intel Core i3, i5 or i7 CPU is the right choice for you and this buyer's guide is here to help.

Thinking of building a new PC around Intel’s high-end Core i9 processors? Check out our guide to Which Intel Core CPU is best here. 

Core i3, Core i5, Core i7 — the difference in a nutshell

If you want to boil things down to something plain and simple, then generally speaking, "most" Core i7 CPUs are better than most Core i5 CPUs, which are in turn better than most Core i3 CPUs. 

Below that, you’ve got fare like the Intel Celeron and Intel Pentium processors. We’re not going to go to deeply into those and how they compare to Intel's Core proecessor, since this article is specifically focused on the difference between Intel’s Core i3, Core i5 and i7 CPUs - but they do merit a mention.  

If you're building your first PC, the main thing you need to keep in mind here is that the 3, 5 and 7 attached to each family of Intel Core processors are simply meant to be indicative of their relative processing power. They’ve got nothing to do with the number of cores in each CPU nor the speed of each. Intel’s Core i7 CPUs don’t have seven cores nor do Core i3 have three cores.

Which family an Intel Core CPU falls into is based on a collection of criteria involving their number of cores, clock speed (in GHz) and cache size, the number of Intel technologies they integrate also plays a role. In other words, you’re much less likely to find things like Turbo Boost and Hyper-Threading in an i3 processor compared to an i5 or i7 processor. 

At the most basic level, these numbers reflect where each class of Intel Core CPU sit relative to one another and are intended to give consumers an idea of the kind of performance they should expect from each. 

Essentially, the idea that Intel are looking to convey with this CPU classification system is that PC builders should expect:

• An Intel Core i3 to provide adequate performance for basic tasks

• An Intel Core i5 to provide good performance for most tasks

• An Intel Core i7 to provide great performance for the most demanding of tasks

Since some older i7 CPUs might not out-perform more recent i5 CPUs, these designations shouldn’t always be taken as gospel but if you’re after a short and easy way to understand which processor is better, the numbers attached to each Intel Core family serve nicely.

Intel’s Core i3, i5 and i7 processors can also be grouped in terms of their target devices. Some are intended for us inside laptops, others are intended for use with desktop PCs. Wattage is the big differentiator here, since CPUs inside mobile devices generally have to make do with less power draw,

In some cases, the difference in specs and performance for the desktop and laptop variants of Intel’s i5 and i7 CPUs can be quite significant. However, to avoid confusion, let's start by exclusively talking about the desktop variants. 

Number of cores

While the number of cores inside an Intel Core CPU isn’t everything, the more cores there are, the more tasks (known as threads) can be served at the same time. This means that a PC with a higher core-count is going to be better for tasks where multithreading is important, such as web servers, web browsers and some video games.

While there isn’t a hard and fast rule around it, you’re also more likely to find less cores in a Core i3 than you are a Core i5 or i7. With a few exceptions, such as Intel’s 8th Gen Core i3 “Coffee Lake” CPUs, most Core i3 CPUs only have two cores. 

The reason for this is that i3 processors are designed to hit a lower price-point more than they are push boundaries for performance. They tend to be found inside PCs that target a more budget-conscious market-segment where the need for a device to be affordable eclipses the demand for higher performance. 

As you’d expect, Intel’s Core i5 processors tend to be more powerful than their i3 counterparts. Part of this comes down to faster average clock speeds. Part of this comes down to additional cores. More cores means these CPUs can handle more threads at once and faster clock speeds mean they can complete tasks more efficiently.

In years past, Intel’s Core i5 CPU line-up has generally been built around CPUs with up to four-cores. However, in recent times (like the 9th-Gen Coffee Lake refresh), Intel have upped the ante to six cores for many of their i5 CPUs. This includes stuff like the Intel Core i5-9400, Intel Core i5-9500 and Intel Core i5-9600. 

Lastly,  you’ve got Intel’s Core i7 CPUs. Again, you’re looking at both faster average clock speeds and additional cores. Intel’s Kaby Lake i7 Core CPUs included only four cores but the more modern Coffee Lake family of i7 CPUs feature up to eight cores and standard clock speeds that range go up to 3.6Ghz. 

At this point, you may be wondering just how important clock speeds are. The answer: pretty important. However, when it comes to clock speed, there are a few things you’ll want to keep in mind. 

The first is that, in general, a higher clock speed is better. However, due to the thermal issues involved, processors with more cores tend to operate at a lower clock speed.  Often-times, choosing a CPU involves choosing between a CPU capable of delivering faster clock-speeds or choosing one with more cores.

This brings us to the second thing you’ll want to keep in mind: faster might be better but it's not always necessary. Although a faster core might be more efficient than a slower one, it might not necessarily be better for the tasks you want to use your computer to be better at.

Many applications only run single-threads while others are designed to utilize multiple. For cases where the latter applies, such as video rendering and gaming, having more cores is going to offer up an enormous improvement over having faster ones.

Rather than run out and dropping the cash on the CPU with the fastest clock speed you can find, it might be worth thinking about what the clock speed you actually need looks like. To that end, it's worth looking up the recommend system specifications for the game or software you'll be running on your new PC.

For more everyday things like web browsing, an i5 processor with a higher clock speed is probably going to offer more bang for your buck than a beefier i7 might. Still, sometimes it’s more important to have those extra cores than an i5 or i7 CPU includes and often-times the choice between one Intel Core CPU and another will come down to whether you want to have a CPU with more cores or one with better clock speeds.

Are you building a PC that does the things you might do or are you happy to settle for one that can do the things you need it to do?

The other thing you’ll want to factor in here is that there’s an important difference between a CPUs standard clock speed and turbo clock speed. The former is the normal clock speed that an Intel CPU is able to deliver. The latter refers to the fastest speeds it can reach using Intel’s Turbo Boost features.

These sorts of technologies, found exclusively in Intel CPUs, are one of the key things that separate i3, i5 and i7 processors - since the more-affordable i3 CPU (plus some i5 CPUs) often don’t include them. 

Find out more about Intel Turbo Boost, Cache size, Hyper-Threading on the next page.

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