Why You’ll Probably Never Own A Mac With An ARM Processor [Feature]


Image via Ars Technica

Ever since Apple launched the new MacBook Air, analysts and Mac fans alike have gone wild speculating that Cupertino might dump Intel and use custom-made, ARM-based chips in their laptop line instead. Yesterday, more fuel was thrown on the fire when it was revealed that an Apple intern worked on porting OS X to ARM devices back in 2010. Even Intel has said it would be “remiss” of them to dismiss the possibility that ARM might steal their Apple business. On the surface of things, it looks like ARM might make its way to our MacBooks soon.

Is ARM really a threat to Intel? Yes, absolutely, and especially as we transition into Apple’s Post-PC world. But there is next to no chance Apple will replace Intel chips for ARM-based ones any time in the next five years. In fact, there’s a good chance the exact opposite could be true, and Intel chips will be powering our iPhones and iPads by then. Here’s why.

Where ARM’s Power Efficiency Comes From

For most people, it’s not immediately clear what makes the chip inside your iPhone (an ARM-based chip made by Apple) different from the processor inside your MacBook Air (an Intel chip). So here’s a remedial layman’s primer.

All other things being equal — and as we’ll see later, all things are not equal — the main advantage ARM chips have over Intel ones is power management. But why are ARM chips so much more power-efficient than Intel’s that they can be used in the iPhone?

It’s because of a fundamental difference in the chips’ architectures. ARM’s RISC-based architecture has a distinct edge in power-efficiency over Intel’s x86, which was designed in the late 1970s. While computer architecture is a complicated thing, for the most part, RISC is more power efficient than x86 because it has to spend less energy figuring out where one instruction ends and the next begins.

With x86, an instruction to the chip can be any number of bytes. That means in any 64-byte chunk of memory, you can have any number of instructions… and as a result, a computer chip has to spend energy separating instructions before it can process them. With RISC, though, every instruction is 4 bytes: the chip knows that every 4 bytes, it can expect to see a new instruction. It doesn’t have to work as hard figuring out the grammar. Physically, this manifests itself in an ARM chip by allowing you to make your CPU cores smaller than their x86 counterparts, and for these CPU cores to draw less power.

Think of it like this. Which of the following sentences is easier for you to read?


The cat sat and ate his hat.

The second sentence is clearly easier to read than the first, because in the first sentence, there are many different types and lengths of words all crammed together. In the second sentence, all the words are spaced apart, and each word has exactly the same number of letters. A child can read the second sentence easily, while the first sentence would challenge many adults.

Again, we’re making this a lot less complex than it actually is in the interests of accessibility, but for the most part, the difference between the way RISC and x86 pass along instructions is like this example. An instruction passed along in RISC takes less energy to compute, and can be understood by a smaller, less advanced chip.

Those are all big advantages… but unfortunately, they have diminishing returns.

ARM vs. Intel

As we’ve seen, ARM is better than Intel chips at decoding instructions. But there are two other things every chip needs to do: execute those instructions, and put them into memory. And Intel has the advantage there, says David Kanter, principal analyst and Editor-In-Chief at Real World Technologies, a technology analysis firm specializing in x86 and RISC microprocessors.

“If you look at any modern, high-performance chip, what you’ll find inside is maybe 25% to 35% CPU cores, 35% to 45% cache memory, and the rest is other stuff like memory control, I/O and so on,” Kanter told Cult of Mac in an interview last year. “So while ARM can make their CPU cores about 20% smaller and more power-efficient than Intel can because of RISC, all things being equal, that’s only a really tiny advantage overall. Maybe 4%.”

And that 4% advantage disappears the second you put Intel’s massive manufacturing muscle into the equation.

Intel is the Apple of the microchip world: everyone is at least a year behind Intel when it comes to competing with their cutting-edge technology and design in the x86 space. Because of Intel’s manufacturing strengths, they can make the entirety of their chips smaller (and therefore more power-efficient) than anyone else around, not just their CPU cores.

The result? Intel’s CPU cores may need to be slightly bigger and less efficient than ARM’s, but the overall chip is smaller and less power hungry at the same speeds.

So why is Intel so behind ARM in the mobile space? Simple: Intel screwed up. Over the last decade, Intel spent years focusing on performance over power management, desktop over mobile. They were so focussed on winning the x86 Gigahertz war against the likes of AMD that they didn’t see the rise of ARM and Apple’s Post-PC world coming.

But Intel’s now seen the light. They have almost infinite resources to throw at the problem of catching up. And they’re going to do so quickly.

“By 2014, Intel will have gotten their power management ahead of everyone else and be using their manufacturing muscle as a major advantage in the mobile landscape,” predicts Kanter.

And when that happens, most of ARM’s advantages over Intel will go away, save one: Apple can design and tweak its own ARM chips to its heart’s content, adding all sorts of custom low-power graphics solutions and oddball sensors to the chip. That’s harder to make happen with Intel.

Chip mod-ability is a compelling reason why Apple will likely stick with making their own ARM-based, A-series chips for mobile devices. But when it comes to a laptop or desktop Mac form factor, getting these things baked into the chip itself isn’t as important, when you can add other hardware or software to manage the same tasks.

There Is No Threat To Intel From ARM In The Mac Space

“The fact is that there is no ARM processor today, nor any that will be coming in the next five years, that are suitable for Apple’s existing models of laptops and desktops,” says Kanter. “On a deep and profound level, there is no technical advantage right now for Apple to switch to ARM across its laptops and desktops.”

Why? ARM processors are still relatively slow, and unsuitable for the vast array of tasks we take for granted in a desktop or laptop. Compared to the Core i7 in your MacBook Air, the core of Apple’s A5 CPU is similar to that of a 1995-era Pentium Pro. A full-featured port of OS X simply can’t run on an ARM series chip right now, which is what gave us all iOS — a massively stripped down version of OS X — to begin with.

“Apple won’t use ARM in the MacBook Air or any other Mac laptops anytime soon, because by the time you’re done making compromises, you’d end up with an iPad,” says Kanter. And even if ARM chips could be quickly ramped up to match the power of Intel’s current chips, it’s not clear that they would be any more power efficient than Intel’s offerings.

But ARM doesn’t need to replace Intels in Macs to beat Intel. While Mac sales are booming, iPhone and iPad sales are exploding. So although Apple’s Mac business is very healthy, it’s becoming a smaller part of the overall pie. Last quarter alone, Apple sold 37 million iPhones and 15 million iPads compared to a mere 5.2 million Macs. If iPads and iPhones continue to overshadow PC sales, ARM doesn’t need to come to Macs to be a very real and very scary threat to Intel.

All the more reason for Intel to get serious about power management now and figure out how to more closely work with companies like Apple to offer an easier, more streamlined way to insert their own custom technology into Intel’s x86-based chips. But Intel knows they’re behind and are taking the lessons they’ve learned from ARM over the last few years seriously. More importantly, Intel has the resources and expertise not just to catch up, but to blow the competition out of the water in the next few years.

So Why Was Apple Working On An ARM Port Of OS X?

If ARM isn’t really suitable for running OS X, and if the power advantages of ARM mostly disappear when you make the chips as fast as Intel’s offerings, then why was an engineer working on porting OS X to ARM back in 2010?

We can only speculate, but there’s any number of reasons that an intern might be tasked by Apple to explore this route that don’t end in a commercial product. We already know that Apple puts new engineers on fake products until they can be trusted. It’s also possible that Apple would want a bare-bones version of OS X that they could show Intel to help at the negotiating table. Finally, Apple may have simply been doing preliminary groundwork in case of the eventuality that ARM does catch up to Intel in five-plus years or so.

(Update: Seth Weintraub from 9to5Mac wrote to inform us that the real reason Apple had an intern working on porting Darwin to ARM was to update Airport platform, which has devices running Marvell ARM-based chips. In other words, as we’ve said, moving the Mac to ARM had nothing to do with it.)

Apple’s not serious about ditching Intel for the Mac, but even so, the next few years will be very interesting as ARM and Intel trade body blows. If Intel plays its cards right, come 2015, we could all be talking very seriously indeed about whether or not Apple will be putting Intel’s new mobile chips in the iPhone 8 and iPad 6.

[image via Ars Technica]

[teaser-top]But could someday have an iPhone with Intel inside.[/teaser-top]
[teaser-featured]But could someday have an iPhone with Intel inside.[/teaser-featured]