Published: March 15, 2013 1:13 PM
By Régis Jehl
Translated by: Catherine Barraclough
Samsung's freshly unveiled high-end Galaxy S4 smartphone is the firm's first mobile to run on an eight-core processor. But what's so good about all those cores?

Samsung Galaxy S4
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Samsung has chosen to load its Galaxy S4 with different mobile processors (SoC) depending on the region of sale. In some markets, the handset will run on a 1.9 GHz quad-core Qualcomm Snapdragon S600 (Krait 300), while in others it'll get Samsung's Exynos 5 Octa 5410. As its name suggests, the Exynos Octa is an eight-core processor, but technically it has two groups of four cores. Note too that this technology isn't exclusive to Samsung. It's actually a practical application of ARM's big.LITTLE solution, and it's something that LG is also set to use a little further down the line with its Optimus G2 handset. It basically involves grouping together two sets of four CPU cores, one made up of very fast but very power-hungry Cortex A15 (1.2 GHz max.) cores, and the other made up of slower, lower-power Cortex A7 (1.6 GHz max.) cores.

At first glance, it's easy to assume that Samsung is simply thinking "the more cores the better". In reality, there's more to this processor that meets the eye, as the big.LITTLE architecture allows processors to offer high levels of performance while keeping power use to a minimum.

The processor can work in various ways to manage power use and performance

Arm big little CPU core use
To optimise power use and performance, the chip can work in various ways. As shown in the diagram above, the Exynos 5 Octa can use just some of its Cortex A7 cores when only low levels of processing power are required (e.g. standby, looking at photos, listening to music). The remaining cores stay idle, keeping power use very low.

When dealing with more demanding tasks, like running video games, the eight cores can all be called into action to ensure maximum levels of performance. However, this will inevitably go heavy on the phone's battery, and may well use more power than the Galaxy S3 in the same conditions. That said, Samsung hasn't confirmed that the chip will run full-whack with all eight cores, and it's possible that the " top performance" mode could involve running four A15 cores instead.

Several intermediate combinations are obviously possible too, with various groups of cores active or idle in relation to the task in hand. Plus, it's not the Android OS that decides which cores need to be active or idle here, but the processor itself. The big.LITTLE system is therefore hardware-driven rather than being software-driven like the fifth core in Nvidia's Tegra.

The Exynos 5 Octa 5410 is a mobile chip that effectively adapts to juggle power efficiency and performances for optimal operation. Still, it remains to be seen exactly what effect this will have in the first smartphone to use this kind of chip, the Samsung Galaxy S4 (which, as it happens, comes with a powerful 2600 mAh battery).

It's also interesting to consider what kinds of apps or functions could potentially make use of the eight cores all working together. When presenting the S4, Samsung showed off all kinds of interesting functions (Dual Camera, Dual Shot, Dual Video Call, Dual Recording, S Translate, S Voice etc.) but it's as yet unclear whether or not a standard quad-core processor (e.g. Cortex A9) or a new-gen dual-core model (e.g. Cortex A15) would be just as capable of handling those tasks. And for games, the most important factor remains the graphics chip (PowerVR SGX544MP3) rather than the CPU. These are certainly interesting questions. And we'll no doubt look into them in more depth soon on DigitalVersus.

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