Saving Power Without Giving It Up

21 August, 2013 03:29PM · 5 minute read

Part of engineering design and product development is compromise. The difficulty is choosing which compromises to make and why. To understand which are the right ones to make we consider end user use cases. How will they use the product? When and why will they use it? The answers to these questions should drive the design of the product in question. If they don’t, chances are that most people won’t be satisfied by it and the product will ultimately fail. As designs evolve over time, good companies keep re-asking those very questions as technology changes, peoples needs change and thus so should products change with them.

Much has been discussed about Moore’s Law and David Houses observation that computer power doubles every 18 months and how silicon is reaching its limit beyond which the process simply can not continue. There are competing technologies vying for a place in the silicon dominated computing world but most are many years away from being mass-producable or even financially viable. Anticipating this approaching road-block, operating system and software developers are moving towards more parallel processing with multi-core CPUs now standard on desktop, laptop, tablet and smartphone platforms around the world. In order to keep reducing the size (and hence increasing the density) of CPUs, smaller and smaller processes must be used (45nm, 32nm and Intel Tick-Tock), but in order to use them their average clock speeds must be reduced. At this stage it has become more about increasing/compressing/multi-processing tasks rather than striving for additional computational speed.

The paradigm shift recently is that it is no longer about CPU “power” previously equated with speed, but rather CPU “power” as it relates to CPU power consumption. The smaller we shrink, the less power we use and with architectural improvements we maintain the same level of computational performance overall. Within the boundaries of the laws of physics this can only be a good thing as these devices can now power an advanced smartphone and still have a battery life of up to a day1.

As the mobile computing revolution has pushed for lower and lower powered mobile CPUs, the desktop/laptop CPUs have also been advancing in a similar direction and we are now rapidly approaching an inflection point in the computing industry when powerful CPUs are no longer the driving force but rather, less power consuming CPUs.

There was a time when each new version of popular software (like Microsoft Office and web browsers) needed a little more computing power than the previous version. Operating systems as well started out with outline dragging windows, then progressed to full frame rate window and content dragging, and then to shrink/spin/genie 3D window effects that each required still more hardware power with each operating system upgrade. Recently the move has been to offload the graphical components to the GPU leaving the CPU for running software and computational tasks and there are now many good low-power GPUs available that provide satisfactory performance as well.

Perhaps it is impatience but looking around the PC market place for the last 5 years, operating system upgrades have not required hardware upgrades for performance reasons when using the major operating systems2

This situation has many people asking themselves, if it’s not about CPU “power” in the traditional sense, what actually matters in a computer now? Interface usability? Screen size? Power consumption? Perhaps it’s all of these or some others but let’s focus on power consumption. Around the world there is an increasing energy shortage. Driven by market forces and companies wishing to maximise profits the keepers of the energy are the holders of the keys in our modern world and that energy is no longer cheap. In some cases the cheaper resources have long since been used and the resources in use now are more costly to extract. There is also a mounting series of evidence giving credence to the theory regarding global warming and even if that energy is created from Nuclear Fission, polluting the world with concentrated radioactive waste seems to also be a questionable approach.

Thus energy usage is increasingly on people minds for one of two reasons3: 1) Energy costs money and the current world economy has pushed peoples budgets hard so every cent counts; 2) Saving energy reduces the amount of pollution released into the environment as we simultaneously switch to renewable energy sources.

The MBA this article is being written on has a 2.0GHz Core i7 CPU which consumes 17W at Idle4 and 48W at full load5 which we compare with my Mac Pro6 at 130W at Idle and 240W at full load. At 23c/kWh that difference is staggering when you consider that apart from the occasional video encoding, the MBA does just fine - even compiling in Xcode it keeps enough pace with the Mac Pro that it’s good enough for my needs.

With Apple introducing Timer Coalescing in 10.9 of OSX “Mavericks” and the rollout of Intels Haswell CPUs across their machines7 it’s clear that Apple sees the future in low power computing. They in particular seem to be reassessing customers needs and focussing on lower powered devices across their product lines. With all of this in mind, before you purchase your next computer ask yourself a serious question: How much “power” do you really¬†need?


  1. Backlit screens also draw considerable power and it’s not just the CPU [return]
  2. Windows 7 performs quite well on a Pentium 4 machine [return]
  3. maybe both, who knows [return]
  4. Full screen brightness, web browser open, Microsoft Word document open, not charging [return]
  5. Handbrake 1080p video encoding [return]
  6. Quad-core 2.66GHz Nehalem [return]
  7. Currently MBAs only but it’s expected to be rolled out to their other non-MacPro models shortly at Intel production rates increase later this year. [return]