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Marvell Launches First Triple-Core Hybrid ARM Chip
Blacklaw passes along an excerpt from Thing.co.uk that begins "While other manufacturers are content to develop dual-core ARM processors, Marvell has gone one better — literally — with a new triple-core chip called the Armada 628. The system-on-chip design, based on ARM's v7 MP series, features two dedicated 1.5GHz processing cores plus a third 624MHz core in a single application processor — making Marvell the first company to bring such a beast to market. While two of the cores are a pretty standard SMP setup, as seen in other dual-core ARM implementations, the third is a standalone processor designed for ultra-low-power draw. The idea behind such a design is that when the system is idle, or only running a low-performance application on a single thread, it can shut off the dual-core portion and save oodles of power."
It's common for people (myself included) to conflate Energy with Power, but it's often an important distinction. To begin with, technically, we don't consume power. We consume energy (to do work, which is in the same units), and power is the rate at which it is consumed.
An important factor often left on the floor is processing efficiency, meaning how fast are we getting work done for a given power level. If you reduce power by half, but the work takes twice as long, you've accomplished nothing. For the same amount of work, your battery will drain the same amount. Indeed, what we really want to do here is make systems take less energy, and within reasonable limits, it doesn't matter how much power you consume while you're doing it.
This has actually been one of the things that makes ARM processors energy-efficient. Not to say they're not also low power, the strategy has always been to build event-driven systems. Something happens (user input, sensor reading, etc.), which causes the CPU to wake up in your embedded system. The ARM processor then blasts through the work to be done, and then goes to sleep, powering down completely until the next event. (Some systems will use intermediate "sleep" states that are less time-expensive to sleep and wake.) An ARM is more efficient than an Atom, in part because it uses less power, but also in part becauses it needs less time to complete the same task.
In today's technology, this is especially important. At 90nm and 65nm, the Intel Core and Core 2 used clock gating to save power. Functional units (e.g. floating point multiply) that are idle have their clock signals gated, which reduces power being used by that part of the clock distribution tree. This is important because in those technologies, dynamic (switching) power dominates. In the Core i7, Intel uses POWER gating. When a functional unit is idle, it's powered down completely. This is because in 45nm and 32nm CMOS, static (leakage) power is what dominates.
Going back to ARM, this is something being applied in the Cortex A9. They've made a more complex processor in order to execute out of order, but as a result, computation goes appreciably faster. During computation, leakage is constant. By getting the work done faster and powering down completely, more leakage power is saved. Less time translates into less energy, even if the A9 uses more power than the A8.