Since the introduction of the Apple iPhone 5S with the 64bit Apple A7 processor, it's become something of a status symbol to have a 64bit mobile applications processor. Intel, Mediatek, Nvidia, and Qualcomm either announced 64bit plans before or during the Mobile World Congress here.

While there's no proof that mobile devices are ready for 64bit code, the Apple introduction has kicked off a flurry of 64bit chip announcements that continue through the 2014 Mobile World Congress. The rush to 64bit mobile processors is on.

Does 64bit ARM processors make any sense in a 2014 smartphone? Or is '64bitness' the next big marketing check-off box for smartphone chip makers? But will consumers of high-end smartphones be clamoring for 64bit processors, like the one found in the Apple iPhone 5S? The answers are: somewhat, clearly, and uncertain. In addition, there's going to be an uneven introduction of 64bit processors in the market.

The utility of a 64bit processor in smartphones and consumer tablets has been subject of debate. An executive of one chip company called it a "gimmick," but soon afterwards his employer disavowed that categorisation.

Apple's 64bit iOS and application code takes advantage of the more efficient ARMv8 instruction set, but it's hard to separate the influence of the new instruction set from the other microarchitecture changes that Apple made in the A7 when comparing it with other 32bit ARM processors.

Intel is also promoting 64bit support in its latest Atom processors build on the 22nm Silvermont core. But 64bit instruction sets are not only useful to address larger memory arrays, both ARM and Intel have solutions for paging schemes to support more than 4GB of RAM in their respective 32bit instruction sets.

In both the ARMv8 instruction set (and to be more exact, the AArch64 mode) and the Intel x86-64 instruction set there are enhancements to the chip microarchitectures that improve performance and break through limitations of the 32bit versions. The ARMv8 and x86-64 instructions offer significantly more register resources and add new capabilities such as improved virtualisation support.

While Apple recompiled its iOS operating system and core applications for 64bit, neither Google's Android nor Microsoft's Windows Phone operating systems are 64bit enabled. Both Intel and Nvidia have demonstrated Android recompiled for 64 bits, but only not as a released operating system and Google has not announced native 64bit support.

Microsoft has also not revealed a 64bit roadmap for Windows Phone OS. The lack of a 64bit operating system is only a temporary problem as 64bit operating systems lagged the introduction of 64bit capable PC processors and the ARMv8 instruction set include 32bit backwards compatibility through the AArch32 mode.

The lack of a native 64bit operating system has certainly not slowed chip manufacturers from announcing 64bit mobile processors. Prior to MWC, Apple, Nvidia, and Qualcomm had announced 64bit mobile ARM processors.

At MWC, MediaTek announced its entry into the 64bit processor market with the MT6732 quad core smartphone processor with integrated LTE modem announced the day before the start of MWC (MediaTek's MT67xx product nomenclature is for 64bit ARM processors; 32bit parts are MT65xx).

Nvidia had demoed its chip, a variant of the the Tegra K1, at 2014 CES. The Nvidia chip will have two wide-issue, custom 64bit "Denver" cores.

Qualcomm also added to its 64bit product line with the Snapdragon 610 and 615 processors. The Qualcomm chips use ARM's licensable Cortex-A53 CPU cores in the Snapdragon 410, 610, and 615.

The Cortex-A53 is the 64bit evolution of the 32bit Cortex-A7, the little core in the big.LITTLE system architecture that can be paired with the Cortex-A15 or Cortex-A17 big core.

There is also a 64bit big CPU core, the Cortex-A57, but that seems destined for ARM server chips like AMD's eight core Opteron A1100 because of its higher die area and power requirements—at least in the short term. A number of low-to-mid-range mobile chips use from one to eight Cortex-A7 cores.

The new chips announced by MediaTek, like the one announced by Qualcomm use the 64bit capable Cortex-A53 for mid-range smartphones. While the Cortex-A53 is not the highest performing mobile CPU in ARM's arsenal, it offers good performance through a dual-issue microarchitecture and clock speeds up to a consumer friendly 2GHz in 28nm. Intel's Atom processors are also 64bit enabled.

Does 64bit make a difference to consumers today? The short answer is not very much—so far.

As a chip geek, I found the idea of having a 64bit processor in my smartphone compelling enough to buy the iPhone 5S, but I doubt other consumers were as enticed by an arguably esoteric feature of the phone. But in the long run, much like the PC market, 64bit will become pervasive in high performance mobile processors.

Until native 64bit Android is available, the possibly premature jump to 64bit cores in mobile processors shipping late 2104 and into 2015 will create an awkward product positioning issue—mid-tier smartphones will appear with quad, and likely, octal 64bit Cortex-A53 ARM cores and high-end phones offering custom 64bit CPUs, but some higher-end smartphones will also use the recently announced 32bit Cortex-A17 CPUs (like the MediaTek's octal-core MT6595).

Mobile processors based on the Cortex-A17 will offer higher clock speeds and higher performance than those based on the Cortex-A53 (when running 32bit operating systems), but the A17 cannot provide the 64bit check-off box of the A53.

The consumer market conundrum will be which to buy: 64bit capability or higher performance? While operating systems only support 32bits today, the higher performing choice is clear. But once 64bit Android and Windows Phone is released, the Cortex-A53 offering adds additional value.

For a period of time the two chip solutions for mid-to-high end smartphones will have to awkwardly coexist. The one thing that is clear is, with the large diversity in the Android ecosystem, the transition to 64bit will not happen overnight and there is still a lot of room for 32bit processors.

By: DocMemory
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