There 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’s 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.