ARM seeing more mobile chip manufacturers using its big.LITTLE architecture

February 26, 2013
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    think big.LITTLEThere are several reasons why ARM has been successful on mobile devices (while others like Intel have¬†struggled). One of the key reasons is the low power¬†consumption¬†of the ARM¬†architecture. However ARM is fighting an on-going battle between¬†performance¬†and power usage. In simple terms the higher the processor performance, the more power is used. High power¬†requirements¬†aren’t good for mobile devices which rely on batteries, rather than mains power like desktop computers.

    Instead of just upping the Megahertz and seeing the power usage go up (something that happened on the PC for a number of years), ARM are taking a different approach and has developed an architecture called big.LITTLE. This clever idea couples a high performance Cortex-A15 processor with an efficient Cortex-A7 processor. When the mobile device is doing easy work the power conscious processor is used, but when something demanding happens the device switches to using the higher performing Cortex-A15.

    Since both the A7 and the A15 can be multi-core this effectively means that a quad-core A15 coupled with a quad-core A7 yields a eight core CPU, well almost.  You see only one core, of the coupled pair, is used at a time, either a core in the A7 is in use or its counterpart in the A15. So strictly speaking big.LITTLE processors are quad-cores CPUs with a choice of eight cores on which the OS and apps run!

    So far the biggest proponent of the¬†big.LITTLE¬†architecture is Samsung which announced it will be used in its¬†Exynos 5 Octa. It is¬†thought that the Exynos 5 Octa¬†will power the next Samsung¬†Galaxy¬†Note (but not the Galaxy S4). The use of the word “Octa”, implying eight cores, has been¬†criticized¬†by¬†Qualcomm’s CEO Paul Jacobs who has called Samsung‚Äôs Exynos 5 Octa a PR stunt. But name calling aside,¬†ARM has also announced that¬†five more companies including CSR, Fujitsu Semiconductor and MediaTek have licensed the big.LITTLE architecture.

    Will the big.LITTLE¬†architecture¬†make a¬†difference? ¬†Almost certainly yes. If ARM’s data is right then the A15 is about twice as fast as the A7 but the A7 is three times more¬†energy¬†efficient¬†that the Cortex-A15, so switching to the A7 (which itself is running at a¬†respectable¬†1.2Ghz) for lesser tasks should produce a power saving of¬†up to¬†70%.

    It is interesting to note that the performance of the smartphone has increased 60 fold since 2000 and 12 fold  since 2008. I guess we should all be grateful to ARM for making that possible and for continuing to innovate.

    Comments

    • kascollet

      Truth ?
      A15 is a BAD mobile architecture. Powerful but vampire hungry. Having to pair each of those A15 cores with another battery friendly one is a miss.
      Qualcomm and Apple understood this soon enough to engineer their own ARM powerful AND energy saving tech, the others will just struggle.

      • MasterMuffin

        OEMs use Qualcomm because of the built-in connectivity features, not because A15 is bad. And Apple, well Apple is Apple…

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