Is Windows 7 greener? Yes, but only by about €50 a year.

Over the last five years I've worked on and off with one of Microsoft UK's most genuine Windows commentators. Paul Foster doesn't have a hint of the 'evangelist' about him and our conversations usually stray between emerging Windows functionalities, to what the latest developments are within his home robotics construction lab.

With arrival of Windows 7, even dedicated OS X users like me are taking a look under the bonnet. Of course it would be inappropriate for me to suggest that Mac users might like what they see due to the fact that Windows 7 is more than just slightly reminiscent of Leopard (snowy or not) – so I won't do that.

But 'jump lists' and fancy icons aside, exchanging a few mails with Microsoft's Foster, he was keen to highlight a set of Windows 7 features rather closer to the engine room. Namely: Windows 7 power saving features. Here's a list of strongest contenders for attention in this area:

• Idle Resource Utilisation • Trigger start services • Enhanced processor management • Timer coalescing • Device power management • Adaptive Display Brightness • Low-power audio • Bluetooth power improvements • Networking power improvements • Power efficiency diagnostics • Power policy • Group policy

Foster points out that some of these features have been implemented to take advantage of newer processors and devices. So users opting for Windows 7 to breathe new life into older kit (something that the new OS can apparently do) will not be be able to get the full benefit from these features.

So how does it do what it does? Foster explains, “The core theme of power saving in Windows 7 seems to be based on the principal of batching up work. Idle resource utilisation, timer coalescing and enhanced processor power management all work as part of this ethos.”

This is due to the fact that modern processors use very little power when they are idle, but they do use power switching from active states to the idle state and back again.

“The trick therefore, is to ensure that the processor can remain in the idle state for as long as possible,” says Foster. “To do this, activities that would interrupt the processor from idle state are gathered together or delayed until really required.”

Essentially, if you take an example and look at something like timer coalescing; USB devices typically work with a polling model, so the device expects to be polled at regular intervals based on the system clock. Many such devices on your machine may have their polling frequency set in such a way that the processor is 'hit' many times for each individual device.

By using timer coalescing, Windows 7 is able to co-ordinate the polling of devices into appropriate batches. This enables the processor to idle and then do all the device polling as a single period of operation

Some of this subject matter also touches on technologies that may be more familiar to the average user such as adaptive display brightness, something people may be familiar with from their use of mobile devices. Dimming an inactive display and/or altering the brightness of the display reactively to the lighting conditions by using an ambient light sensor – if you happen to have one attached to your machine in the first place of course.

According to Foster, “Apparently the display can represent 40% of the power consumed by a computer, so controlling its use more effectively can make for dramatic savings.”

But just how ‘dramatic’ are these ‘dramatic savings’ in real life pecuniary terms Paul?

“At best, the Windows 7 power saving features will save me personally less than €50 a year. Of course, if I was responsible for 1000 PCs in a company, then the potential savings do add up to a significant amount. Looking globally, across all the millions of machines that run Windows today, the power saving potential with Windows 7 is enormous,” he said.

OK so it is a greener option for sure. But you need to take in the big picture if you want to see the true worth of it. Every little bit helps though – doesn't it?

NB: you can read Paul Foster’s own blog linked here.