Why Windows RT has a closed Windows 8 apps environment: power

Office apps are optimized to reduce draw on the battery, extend time between recharging

Windows RT – the ARM-based Windows 8 devices with strict controls on what applications can be loaded – sets longer battery life as a top goal, which goes a long way to explain why Microsoft has placed tough requirements on application development.

The company even had to tinker with the Office applications that come standard with Windows RT in order to make them more power-friendly, and has detailed some of what it went through in an Office Next blog.

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The Windows RT Office apps are based on the same code as earlier versions of Office so Microsoft had to modify their behavior some to cut the amount of power they eat up, the blog says.

Reducing how often the CPU on ARM systems-on-a-chip is woken up can greatly reduce the power used by the device, he writes. Office 2010, for example, under certain circumstances woke up the CPU 1,000 times per minute; that has been cut to 50 when users aren’t interacting with the program, according to the blog.

Office apps have been optimized to use the specialized hardware capabilities of the ARM chips, improving efficiency of the device. For example, tuning video code in PowerPoint to take advantage of dedicated features of the processor cuts power requirements vs what an application adapting to the hardware on the fly via software, the blog says.

Office for RT releases cached content when it detects that an application isn’t being actively used.

Pinching power use even gets to the level of shutting off the blinking cursor a few seconds after users stop interacting with applications.

These Windows RT devices must be made to specifications set by Microsoft in order to achieve the responsiveness and battery life the company seeks. Microsoft’s own Surface Windows RT devices become available when Windows 8 launches Oct. 26 with those of partners becoming available a few months later.

(Tim Greene covers Microsoft for Network World and writes the Mostly Microsoft blog. Reach him at tgreene@nww.com and follow him on Twitter https://twitter.com/#!/Tim_Greene.)