Comparing i3 , i5 and i7 processors

Around 80% of new PCs, and over 90% of laptops, have Intel processors. This means that if you’re in the market for a new computer, you’ll most likely be considering an Intel-powered model.

Finding the right chip is hard. Intel's processor ecosystem is strewn with confusing model numbers that actually tell you a lot about the processor you're about to buy, albeit only if you know what you're actually looking for.

Intel’s branding doesn’t make it particularly easy for you to choose: it’s not at all obvious what the difference between a Core i3, Core i5 or Core i7 processor is, apart from an ever-increasing amount of cash removed from your wallet.

DESKTOP	Core i3	Core i5	Core i7
No. of cores	2	4	4
Frequency range	3.2-3.9GHz	2.2-3.5GHz	2.8-4GHz
Turbo Boost	No	Yes	Yes
Hyper-Threading	Yes	No	Yes
Cache	3-4MB	6MB	8MB

NUMBER OF CORES

The first thing you’ll notice from the table is that Core i5 and i7 processors have four cores, while Core i3 models only have two. Out of all the differences between the Intel processor ranges, this is the one that will affect performance the most.

Each core is effectively its own processor – your PC would still work (slowly) with just one core enabled. Having multiple cores means that the computer can work on more than one task at a time more efficiently, which will help keep your system running snappily even if you have tasks, such as an antivirus scan, running in the background.

Having several cores can also drastically increase the speed at which certain programs run. This doesn’t apply to all applications, as creating software that takes advantage of multiple cores is difficult. While two cores are now the accepted minimum in a processor, if you generally only tend to have a handful of tabs open in a web browser and your most demanding application is a word processor, you won’t see a huge benefit from a quad-core chip. However, modern games benefit from quad-core chips as does video encoding.

As an example, in the Geekbench benchmark, which runs several tests optimised for single-core and for multi-core processing, the quad-core Intel Core i7-3770K machine being used to write this article scored 3,422 in the single-core benchmark and 13,401 in multi-core. With two cores disabled, the score was almost identical in single-core, but dropped to 7,541 in the multi-core test. The maths adds up, halve the cores, (nearly) halve the multi-core performance.

WHAT IS TURBO BOOST?

The next item that may catch your eye is that the slowest Core i3 chips run at a faster speed than the base Core i5 and Core i7 models. This illustrates the perils of making a buying decision based purely on clock speed. Enter Turbo Boost.

Primer: what is clock speed? The GHz figure you'll see represents the number of clock cycles (calculations) a processor can manage in a second. Put very simply, a bigger number means a faster processor. For example, 3.6GHz means 3,600,000,000 clock cycles. This figure should never be used to compare processors from different families, generations or manufacturers, however. Bigger is not better when comparing AMD and Intel, or 2nd-gen to 6th-gen Intel processors: different processor families have different levels of efficiency, so how much they get done with each clock cycle is more important than the GHz number itself.

Turbo Boost dynamically increases the clock speed of Core i5 and i7 processors when more power is required. This means that the chip can draw less power, produce less heat (most of the time) and only boost when it needs to. Turbo Boost means that the clock frequency figures in the table above are misleading. For example, although a top-end Core i3-6300 runs at 3.8GHz compared to 3.3GHz for the high-end Core i5-6600K, the i5 chip can boost up to 3.9GHz when required, so will end up being quicker.

The more a processor boosts its clock speed, the more heat it will produce, so the processors can only Turbo Boost for a limited time while they remain within a certain temperature range. During long periods of heavy processor activity using all a processor’s cores, such as video encoding, a chip may not Turbo Boost much at all as it might be too hot to do so safely. Turbo Boost is a significant part of the reason Core i5 and Core i7 processors outperform Core i3 models in single-core-optimised tasks, even though they have lower base clock speeds.