Haswell, Broadwell, Ivy Bridge. Dual Core, Quad Core, Turbo Boost. Mobile, i5, i7. 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?
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.
Processor names: Haswell, Broadwell, Skylake...
The names Haswell, Broadwell, Skylake and Ivy Bridge are Intel code names for its processor architectures. Ivy Bridge is the oldest, and is used only in the Mac Pro. Haswell was a major re-design of the Ivy Bridge architecture and features on most current Macs. And Broadwell is a relatively minor update to Haswell. It's used in the new MacBook, the 2015 MacBook Airs, and the 2015 13in MacBook Pro. Skylake is due for release later this year.
There are two elements where one processor can improve over 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.
Processor power consumption
The power used by a processor affects us 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.
Apple uses the mobile version of Broadwell, designed to be the most efficient of all, in the new MacBook. The Core M, as it's called, is the first Intel laptop chip that doesn't need a fan to cool it. It's power efficiency is what allowed Apple to build a notebook that's almost ridiculously thin, weighs only 900g, and yet still clocks up 9 hours of battery life while running at a reasonable speed.
Processor speed: dual core versus quad core
The number of instructions a processor can execute in a given time period is determined by a number of factors, including the number of CPUs, the clock-speed of those CPUs and the existence and size of on-board cache. Simply put, and all other things being equal, a CPU with a higher clock-speed (described in GHz) will execute more instructions per second than one with a lower clock speed.
Equally, a processor with four cores will execute more instructions than one with two cores, because it can execute twice as many instructions simultaneously. Thus, a 2GHz quad-core processor should be 'faster' than a 3GHz dual-core model.
Core i5 v Core i7 and Hyper Threading
Intel's Core i5 used widely across the Mac range, and the Core i7, used in the 15in MacBook Pro, are both multi-core families of processors.
The Core i5 tends to be dual-core, although Intel does make quad-core i5s, and i7 desktop processors are quad-core, or sometimes six-core. That's one key difference between Core i5 and Core i7. The others are the size of the cache, the integrated graphics (more powerful on Core i7), and support for hyper threading.
Hyper threading, a feature of the Core i7 series, 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.
Hyper threading isn't the only neat trick the current crop of Intel processors can pull. You might have noticed the phrase Turbo Boost on the Mac specs pages on Apple's website. The simplest way to think of Turbo Boost is as a way of safely over-clocking the cores on a processor.
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 2.2GHz quad-core i7 can, if needed, be pushed to 3.7GHz subject to power consumption and heat dissipation.
Xeon and the Mac Pro
While the rest of Apple's range uses either the mobile or desktop versions of Intel's processor architecture, the Mac Pro uses the workstation model, Xeon. So what's the difference? Workstation processors are designed for raw power, and are less hindered by the need to keep the temperature down (though power efficiency is still an issue). So, the Xeon E5 used in the Mac Pro is available with up to 12 cores, rather than the four available in the Core i5 in the iMac.
The Xeon E5 also supports faster DDR3 RAM than the Core i5 and Core i7, and it has much more L3 cache, meaning it needs to resort to using your Mac's main memory less often. In short, the Xeon can run hotter, and therefore faster than desktop or mobile processors, can execute more instructions per second, and can shuttle data back and forth much more quickly.
Does it matter which processor you choose?
Does the processor you choose make much difference? Yes. And no. Every use case is different and so every user's needs are different. The first thing to note is that your choice of processor will be dictated by the Mac you choose to buy. Not every Mac allows you to choose a processor, and those that do have limited options. You can't, for example, put a Xeon E5 in an iMac.
So the question becomes: is your money better spent upgrading the processor when you order a new Mac, or is it better spent adding more RAM or faster storage? Guess what the answer to that one is? Yep, it depends. If you're going to use your new Mac for 3D modelling, video encoding or financial or scientific modelling, the more powerful the processor the better, and so that's where you should spend your money.
If, on the other hand, you work with huge images in Photoshop, work with large spreadsheets or databases, then more RAM is a better investment than a faster processor.
The good news is that every current Mac comes fitted as standard with a processor that's more than capable of handling almost everything most of us are likely to throw at it.