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The real reasons Apple's 64-bit A7 chip makes sense

Don't swallow Apple's marketing lines that 64-bit chips magically run software faster than 32-bit relics. What the A7 in the iPhone 5S does do, though, is pave the way for Apple's long-term future.

Apple marketing chief Phil Schiller touts the advantages of the A7 processor used in the iPhone 5S.
Apple marketing chief Phil Schiller touts the advantages of the A7 processor used in the iPhone 5S.
Josh Lowensohn/CNET

Apple injected a lot of marketing hyperbole into its claims about the wonders of 64-bit computing when it showed off the A7 processor at the heart of the new iPhone 5S. But there are real long-term reasons that Apple is smart to move beyond the 32-bit era in mobile computing.

The iPhone maker did indeed beat its smartphone rivals to the 64-bit era with the A7, and the processor may indeed vault over its predecessor's performance. The hyperbole came when Apple marketing chief Phil Schiller, speaking at Apple's iPhone 5S and 5C launch event on Tuesday, linked those two accomplishments.

"Why go through all this?" Schiller asked, referring to the new chip and 64-bit versions of iOS 7 and Apple's iOS apps. "The benefits are huge. The A7 is up to twice as fast as the previous-generation system at CPU tasks," Schiller said, and up to twice as fast at graphics tasks, too.

There's a reason the computer industry is shifting to 64-bit computing; the main benefit is memory capacity that can exceed 4GB. But just as we saw with 64-bit personal computers arriving over the last decade, 64-bit designs don't automatically improve performance for most tasks. In fact, there can be drawbacks: it's likely that 64-bit versions of programs will be bulkier than their 32-bit equivalents.

But Apple is smart to lay the foundations for 64-bit mobile computing now, for three reasons. First, large memory capacity is an academic issue in the mobile market today, but it won't always be. Second, the 64-bit transition happens to come along with other chip changes that are useful immediately. And third, it gives Apple more flexibility to build ARM-based PCs if it chooses to embrace an alternative to Intel chips.

What is 64-bit computing?
A 64-bit chip can handle memory addresses described with 64-bit numbers rather than 32-bit ones, which means that a computer can accommodate more than 4GB of memory and that chips can do math with integers that are a lot bigger. The 64-bit transition doesn't have any effect on a lot of computing performance at all.

With servers, 64-bit chips are crucial, because those machines often need gobs of memory for running many tasks simultaneously and keeping as much of it as possible in fast-response RAM. With PCs, 64-bit chips are useful to avoid bumping up against 4GB memory limits, which is about where the mainstream market is today.

On mobile devices, though, the 4GB limit has yet to arrive. Even though having more RAM is really useful, it's got big drawbacks in the mobile market: it's expensive, it takes up room -- and most problematic -- it draws a lot of electrical power and therefore shortens battery life. The Samsung Galaxy Note 3, an Android phone, has an unusually large 3GB of RAM, but it's also got an unusually large size to handle a bigger-than-average 3,200mAh battery.

Better 64-bit math is helpful for tasks like scientific simulations, but it's not a big deal on mobile.

At Apple's event, Epic Games executives were gleeful about the A7 performance playing Infinity Blade 3, and there's no reason to doubt their statements that they could draw a dragon with four times the detail. But that performance improvement is likely to come more from the new graphics abilities in the A7 and from its support for the richer OpenGL ES 3.0 graphics-acceleration interface, not from its 64-bit design.

Schiller pointed to processor performance improvements in the iPhone 5S, which uses Apple's new A7 chip, but didn't detail which speed tests he was using.
Schiller pointed to processor performance improvements in the iPhone 5S, which uses Apple's new A7 chip, but didn't detail which speed tests he was using. screenshot by Stephen Shankland/CNET

Why bother with 64-bit mobile chips?
Even if 64-bit computing isn't some across-the-board speedup technology, there's a very good reason to adopt it: the future.

But here again, we have to splash a little cold water on Schiller's enthusiasm.

"The PC world went through the transition from 32-bit to 64-bit, and it took years," Schiller said. "Today you're going to see that Apple is going to move the mobile computing system forward from 32-bit to 64-bit in one day."

Sure, it only took a couple hours for Apple to announce the iPhone 5S and the A7 processor. But the full 64-bit transition will take years in mobile, just as it did in the PC market.

Indeed, the transition already has been going on for a couple years. In 2011, after four years of behind-closed-doors work, ARM Holdings announced its 64-bit ARMv8 instruction set for the chip designs it licenses to Apple, Qualcomm, Samsung, and many other makers of mobile chips. Apple's A7 uses the ARMv8 architecture.

The hardware change is only the first part. After that comes software. Apple has retooled iOS 7 -- the kernel at the heart of the software, the libraries of prewritten code that it and other software draw upon, and the device drivers the kernel uses to talk to hardware like the network and touch screen -- so that it's 64-bit software. And it's got a version of its Xcode developer tools so that programmers can build 64-bit versions of their iOS products.

But it'll be years before the whole software ecosystem makes the move. Old software likely will never make the change, which is why it's good ARMv8 chips can run older 32-bit software seamlessly. And programmers will still need to build 32-bit versions of their software for older iPhones -- as well as brand-new 32-bit models like the iPhone 5C.

Given how long it takes to make the transition, it's important to lay the hardware foundation early enough that the software market can move gracefully. Even though adding more RAM is hard in mobile devices, it'll happen. It might well happen sooner on iPads, too, which can handle faster processors, bigger batteries, and more elaborate software. And it's possible that computing engineers will successfully commercialize some other form of memory that's not as power-hungry.

ARMv8 benefits
A nearer-term reason the Apple A7 might appeal to programmers has nothing to do with its 64-bit nature: the ARMv8 architecture itself brings some real advantages.

One of them is a larger number of registers -- tiny on-chip storage areas where the processor stores data for very fast access. ARMv8 roughly doubles general-purpose registers from 16 to 31, which means the chip needn't fritter away as many cycles swapping things into and out of memory.

The ARMv8 architecture used in the Apple A7 chip brings several improvements in addition to a 64-bit design, including more registers to store data, better double-precision math, and built-in cryptography features.
The ARMv8 architecture used in the Apple A7 chip brings several improvements in addition to a 64-bit design, including more registers to store data, better double-precision math, and built-in cryptography features. ARM Holdings

When AMD pioneered 64-bit computing on x86 -- a transition it pushed while Intel was distracted with its Itanium designs -- it got a big speed boost from increasing the number of registers. But 32-bit x86 chips were hobbled by having only four registers, while 32-bit ARM chips have a relatively abundant 16; that could mean the performance boost won't be as good with the ARM transition.

ARMv8 also has some other significant changes. It's got much better mathematical abilities, especially when performing the same operation on a lot of data. And it's got built-in encryption processing abilities, which should speed a lot of secure communications and cut battery usage.

New Apple options
Apple surprised the world when it moved its Mac line from PowerPC processors to Intel processors, and there have been rumblings it might move to or at least embrace ARM chips for Macs, too.

The A7 processor or its rumored higher-end A7X sibling might not have enough oomph for a full-fledged personal computer, but it was hard to miss Schiller boasting that the A7 has a "desktop-class architecture." And even if there's never any ARM-based Mac, it's still possible Apple could take iOS into something more laptop-like. The company, which made iWork free with new iOS devices and threw iPhoto and iMovie into the bargain, clearly likes the idea of customers creating content on iOS devices, not just consuming it.

If Apple chose to build ARM-based PCs, having more than 4GB of memory could be very useful. Thus, it would be a big asset to have a mature 64-bit ARM chip design with an accompanying operating system and app collection.

ARM-based Apple PCs would be a dramatic shift indeed. Intel is working furiously on lowering the power consumption of its x86 chips to compete better against ARM, and an ARM-based Apple PC would have serious difficulties running Mac software for x86-based machines.

We need not invent reasons for Schiller's 64-bit A7 enthusiasm besides that it makes a good marketing line, something that sounds like progress and that's easy to see missing from Android competition.

But even if it's mostly just an iPhone marketing line for now, Apple's change to 64-bit ARMv8 designs does make sense in the long run.

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