Android processors: The past, present and future of smartphone chip design

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ARM may rule the roost in the Android hardware world, but it’s not running a dictatorship. Rather than fabricate and sell its own chips, ARM simply designs architectures and instruction sets, which it then licenses to chip manufacturers across the Android land.

It’s a somewhat generous approach, and ARM even encourages its hardware partners to alter reference designs however they like. As a result, companies as diverse as Apple, Qualcomm, Samsung and Nvidia have cooked up their own ARM processor variants, creating something of an arms race.

Thanks to a nudge from Apple and its A7 processor, which was introduced in the iPhone 5s, 64-bit chips will soon be commonplace in Android phones too. Indeed, major players in the Android processor space have already announced both high- and low-end 64-bit parts for 2014. 

But what does all this mean for you? Read on for details and insight. We’ll describe the processors deployed in today’s phones, and preview what’s on deck for tomorrow. Your phone’s ARM chip plays a pivotal role in app performance and battery life, so knowing what’s on the horizon could influence whether you buy a new phone this week, or wait until later this year.

Qualcomm: Snap, the Mighty Dragon

In US markets, Qualcomm leads the way in Android phone implementations with the Snapdragon SoC (System-on-Chip) platform. Snapdragon starts with an ARM-compatible CPU core of Qualcomm’s own design. Currently, the CPU core in Snapdragon processors is called Krait, and is loosely comparable in speed to ARM’s Cortex A15 reference design.

snapdragon 800 diagram

A (very very basic) block diagram of the Snapdragon 800.

Paired with Krait is Qualcomm’s Adreno graphics technology. This GPU line began life at ATI under the brand name Imageon, and was picked up by AMD in 2006 when it purchased ATI. Two years later, AMD sold off the Imageon technologies to Qualcomm, which re-branded them Adreno. It’s a cheeky move on Qualcomm’s part: Adreno is actually an anagram of Radeon, the brand name still used by AMD for its graphics cards. 

Qualcomm was first out of the 4G LTE gate with an integrated SoC implementation for the wireless standard. This put Qualcomm at an enormous advantage in markets like the US, where LTE support became a must-have feature. Direct SoC integration also earned the Snapdragon a home in lots of phones, as the alternative is to add a separate LTE modem chip—thus raising price, energy usage and manufacturing complexity for phone manufacturers.

Currently, the Snapdragon 800 series is Qualcomm’s top offering, featuring up to four Krait cores running at up to 2.46 GHz, and partnered with Adreno 330 graphics. Arguably, this represents the most well-rounded processor package for Android devices today, providing excellent performance in all areas within a reasonable power budget. Snapdragon-based devices also get the lion’s share of post-release ROM development from enthusiasts.

Just around the corner is the Snapdragon 805, a platform refresh that will feature faster Krait cores, an improved Adreno GPU, and faster RAM bandwidth. Oddly, Qualcomm’s first 64-bit mobile parts will arrive this year in the form of the low- to mid-range Snapdragon 410.  High-end parts are expected shortly afterwards. 

Samsung, the company man

Samsung has been producing SoCs based on ARM architectures for more than a decade. In fact, Samsung chips appeared in every iPhone released before the iPhone 4. 

Samsung’s current Exynos series SoCs are fairly traditional ARM variants, featuring Cortex A9 and A15 cores, and ARM’s own Mali GPU design. However, a few Samsung chips—such as the Exynos 5 5410 found in one variant of the Galaxy S4—use PowerVR’s potent SGX core to handle graphics. PowerVR’s excellent GPU designs are most commonly found in Apple products, which is too bad because Exynos could use a little love when it comes to GPU horsepower.

exynos 5 octa

The Exynos 5 Octa features 4 “big” high-performance cores paired with 4 “little” cores that offer lower performance but big battery savings.

While the Exynos 5’s raw CPU performance is generally superior to Qualcomm’s Krait performance, the Mali GPU falls behind competing Adreno and PowerVR graphics solutions. Samsung’s own Galaxy Note 3 implementation is a good example of this. The Note 3 variants featuring Snapdragon chips offer more features and a better user experience, despite being virtually identical to the versions that include Samsung’s own Exynos chips.

A15 cores are power hungry, so ARM implemented a scheme called “big.LITTLE” wherein each high-performance core is shadowed by a lower-power, lower-performance core that takes over whenever workloads permit. The current crop of Exynos 5 Octa SoCs employs this feature to keep the A15’s appetite for power in check, although some implementations of big.LITTLE have cache issues that hinder performance.

Looking forward, Exynos 6 promises to bring cutting-edge 64-bit hardware and integrated 4G LTE to the table. Samsung says the caching problems that held back earlier variants of big.LITTLE have been resolved, and we should see Exynos 6 by springtime, perhaps in the Galaxy S5.

That being said, Samsung’s phones and tablets are most appealing for reasons beyond processor performance, focusing instead on features such as advanced OLED screens and sophisticated stylus input. The conservative route of going with ARM’s reference designs allows Samsung’s engineers to look for more novel ways to differentiate their hardware. Given their market share, it appears Samsung may be on to something with this strategy. 

Nvidia: Full speed and full volume

It may seem like Nvidia has been plugging away with its Tegra line for a while now, but it’s the newest player to the SoC game by a long shot, and the inexperience shows. Tegra’s growing pains meant that very few devices used a Tegra chip until Tegra 3 came along. But the third time was a charm, and Nvidia’s SoC package found a home in tablets like Google’s original Nexus 7 and Microsoft’s Surface. Microsoft retained Nvidia for the Surface 2, which features the Tegra 4, but Google migrated to Snapdragon for the 2013 Nexus 7.

tegra k1 die shot

A die shot of the Nvidia Tegra K1. You can easily make out the four “big” CPUs, one “small” CPU in the center, and the giant graphics array.

Tegra 4 hit the market in 2013 with up to four times the performance of its predecessor, but it still required a separate companion LTE modem chip. It pairs a Cortex A15 quad-core setup with 72 GPU cores of Nvidia’s own design. Still, despite this firepower, GPU performance tends to trail the competition. A fifth, low-power A15 core is also included in Tegra 4 to serve in an energy-saving capacity similar to Samsung’s big.LITTLE.

Tegra 4 isn’t fully competitive with current industry leaders, but waiting in the wings is Nvidia’s Tegra K1, a project that promises to bring last-generation gaming console quality graphics to mobile users with a 192-GPU core implementation of the Kepler architecture. Tegra K1 was announced in two versions. One uses the same “4+1” CPU setup employed in the Tegra 4, with similar ARM Cortex A15 cores.

But the more interesting K1 version uses a custom, dual-core 64-bit CPU code-named Denver, designed by Nvidia’s own in-house dream team of engineers poached from Intel, AMD, Sun, Transmeta, and HP. While leaked benchmarks suggest the K1 may live up to its press, the chip is still a wait-and-see proposition.

For starters, we don’t know which variant of the Tegra K1 generated those leaked benchmarks. And what’s more, we have no helpful details on the K1’s power utilization. With no integrated LTE modem, and Nvidia’s history of relatively high power use, the Tegra K1 may be destined for tablets but turn out to be too power-hungry for phones.

64-bit dreams

While Apple’s move to 64-bit has motivated the rest of the mobile industry to follow, don’t expect to see dramatic dividends in upcoming Android phones and tablets. Apple’s tightly controlled vertical integration—in which system software and device hardware are made by the same company—makes it easier for the company to realize benefits from big platform shifts. And jumping from 32-bit to 64-bit is a big shift. But the transition won’t be quite so seamless in the diverse Android ecosystem.

Some 64-bit benefits, such as increased memory limits, should manifest quickly. But other performance advantages will have to wait until the OS and many applications are modified. And that will require coordination between hardware vendors, software developers and Google itself. This might take a while, but don’t worry about the wait. There’s plenty of mobile tech in the pipeline for 2014 to keep you busy in the meantime.

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