If you are choosing between two different types of Mac, or two generations of the same Mac, you may be wondering just how much of a difference the processors will make. In this article we will endeavour to clarify the differences between the generations of processors, what you can expect from an i5, i7 or Xeon processor, why it matters how many cores you get, and what Turbo Boost really means.

There are so many different terms used to describe the processor in the current crop of Macs that trying to figure out which is best for you is enough to make your head spin. So which processor should you choose? And does it really matter?

What generation of processor is in my Mac?

The names Sandy Bridge, Ivy Bridge, Haswell, Broadwell, and Skylake are Intel code names for its processor architectures. Sandy Bridge is the oldest, dating back to 2011, and Ivy Bridge was an update to that in 2012. Haswell came in 2013 and was a major re-design of the Ivy Bridge architecture. And Broadwell in 2015 was a relatively minor update to Haswell. Skylake first appeared in late 2015 in the 27in iMacs, then in 2017 Kaby Lake processors started to appear.

Currently (as of August 2017) the processor that features in most Macs (with a few exceptions we will go into below) is Kaby Lake. Next up will be Coffee Lake and Cannonlake.

As we said above, the majority of Macs now feature Kaby Lake processors, but there are a few exceptions. The MacBook Air and the Mac mini are still on sale but offer only the Haswell processors from 2013.

The other exception is the Mac Pro, which, since it hasn't been updated since 2013, currently offers an Intel Xeon workstation processor from the Romley platform (which is based on Ivy Bridge). Following on from Romley was Grantley (based on Haswell/Broadwell) and Purley is the next generation (based on Skylake). Purley is due to launch soon and may end up in the new iMac Pro when it launches later in 2017. Following Purley is Cascade Lake which should arrive in 2018, so it is conceivable that it could end up in the new Mac Pro when it launches.

These Xeon workstation processors have different codenames to the processors listed above but are based on the same architecture.

How to choose between processors

Modern micro-processors are incredibly complex beasts, housing more than a billion transistors, each about 0.02% of the thickness of a human hair. And they do far more than the CPUs of old; those took inputs, executed instructions on them, and passed the output to memory. Today's processors are mini-computers, incorporating multiple cores, or CPUs, on one chip, alongside short-term memory, or cache, and even graphics processors.

There are two ways in which one processor can be better than another: the number of instructions it can execute in a given time period, and the amount of power it consumes doing so.

While the former is crucial for some applications, like encoding 4K video, rendering complex 3D models and animation, and some mathematics and scientific applications, for most of us it's the latter which should be of most concern.

The power used by a processor affects the computer in two ways: battery life and heat. Quite simply, all other things being equal, the faster a processor runs, the more heat it will give off and the more energy it will suck from a laptop battery.

Reducing that power consumption and making processors more efficient is at the heart of most of the improvements processor designers such as Intel have made in recent years. As a result, the more recent the processor in a Mac, the more efficient it's likely to be. And that explains why a newer processor will likely be better than an older processor, even if the number of GHz is smaller.

We will look at a number of other differences between processors below, including GHz (the processor speed as advertised, and the speed that can be claimed if Turbo Boost is active).

We will also look at the different processor types in each generation. For example, you can choose from an i5 and an i7 chip.

The other big difference will be the number of cores available, with dual-core, quad-core, and even 8- 12- and 18-cores available. We’ll also examine this below.

How many GHz

GHz reflects the number of clock cycles per second. So a 2.3GHz processor’s internal clock beats 2.3 billion times per second. Hence people referring to the number of GHz as the clock speed.

Each range of Macs usually has more than one option in terms of GHz (with the exception of the MacBook Air which is only available at 1.8GHz, although there is a build-to-order option available that runs at 2.2GHz).

Sometimes it will look like a more powerful Mac has a slower clock speed. This is invariably due to the Mac in question having more cores available. For example, the 2.8GHz quad-core MacBook Pro costs considerably more than a 3.1GHz dual-core model. At first glance that might look like a bad deal, but that’s four 2.8GHz cores, rather than two 3.1GHz cores. And the more cores the better, as we will explain below.

Turbo Boost

Another thing to note in terms of GHz is the Turbo Boost figure. The simplest way to think of Turbo Boost is as a way of safely over-clocking the cores on a processor. This figure can sometimes give a clue as to how one generation’s processor compares to the next.

The Turbo Boost controller samples the power consumption and temperature of the cores hundreds of times a second while monitoring the demands made of them by software. If any of the cores are being driven to their theoretical maximum, Turbo Boost can, if enough power is available and the temperature is at a safe level 'over-clock' the core and enable it to work faster.

So the four cores in a MacBook Pro's 2.8GHz quad-core i7 can, if needed, be pushed to 3.8GHz subject to power consumption and heat dissipation.

And a 1.2GHz MacBook dual core processor can be pushed to 3.0GHz, while a MacBook Air, which uses a much older generation processor, has a 1.8GHz processor but that can only be Turbo Boosted to 2.9GHz.

Core M, i5, i7, and Xeon

Core M

Intel makes mobile versions of its chips. The Core M, which appeared in the first Retina MacBook when it launched in 2014, was the first Intel laptop chip that didn’t need a fan to cool it. Its power efficiency is what allowed Apple to build a notebook that was thin, weighed only 900g, and clocked up 9 hours of battery life while running at a reasonable speed.

There are three Core M processors with increasing performance: Core m3, m5 and m7. The Core m3 features in the entry-level MacBook, running at 1.2GHz. Previously the other MacBook models featured Core M processors, but when Apple updated the range in 2017 it changed the processor in the top of the range model to an i5, and added an i7 as a build-to-order option.

Core i5

The majority of Macs use Intel's Core i5 processors. The Core i5 tends to be dual-core, although Intel does make quad-core i5s - as you will see in the iMac range.

Core i7

However, when it comes to quad-core the i5 and i7 versions are not equal. The Core i7, used in the 15in MacBook Pro and often available as a build-to-order option, offers some features that the i5 doesn’t, one of which is Hyper threading, which we discuss below.

Another difference is the size of the cache, which we will also discuss later.

Thanks to these features, Core i7 processors are better for multitasking, multimedia, high-end gaming, and scientific work.

Xeon

Xeon processors are workstation or server processors. Xeon processors support more memory than the i5/i7 processors, as much as 128GB RAM and more. You will also find more cores available on Xeon processors, 24-cores, for example.

How many cores

Among the Macs on sale currently you will generally find dual- or quad-core options. However, you can get more cores if that is what you need.

The current Mac Pro ships with a Xeon processor with a choice of 6- or 8-cores, and a build-to-order 12-core option. We expect even more cores from the new Mac Pro when it launches in 2018 or beyond. Read all about the new Mac Pro here: Mac Pro release date.

The iMac Pro when it launches later in 2017 will offer 8-, 10- or 18-core Xeon processors. Read more here: iMac Pro release date.

The more cores in your CPU the faster it will perform.

CPU Cache

The more processor cache you have the better. Cache is on-board memory and it helps the processor deal with repetitive tasks faster, because information can be held in the memory. Greater amounts of cache will also help with multitasking, because several tasks can be run simultaneously.

Hyper threading

Hyper threading is a feature of the Core i7 series. It allows the processor to handle twice as many 'streams' as it has cores, by fooling software into thinking it has twice as many cores. So a quad-core processor with hyper threading should be able to execute four times as many sets of instructions in a given time period as a dual-core processor with the same clock speed but without hyper threading.

This means that a quad-core i7 can act like it has eight cores, but a quad-core i5 will only be able to use the four cores available to it.