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Microsoft Details Windows 8's Power-Saving Features

Microsoft summarized many of Windows 8's power-saving capabilities during its Build developer conference in September, when it also unveiled a developer preview of the upcoming OS. Lead Microsoft program managers Sharif Farag and Ben Srour went into further detail about how those capabilities work with applications in a "Building Windows 8" blog post on Tuesday.

The basic idea is that background apps get suspended by the operating system to conserve battery life, which is especially useful for mobile device users. Perhaps the most interesting tidbit explained in the post is that Windows 8, when released as a product, will let the user close an application via touch, keyboard or mouse. This point, seemingly trivial, likely will be a tremendous relief for those who have tried the developer preview tablets given away at Build, which required the user to go find the Task Manager and kill an application in order to close it.

Still, Farag and Srour make a strong case for not closing apps at all when using Windows 8. Apps that a user isn't directly using will get suspended by Windows 8, and while those suspended apps consume some system memory, they draw no power, so there is no battery drain from them "running."

Microsoft makes a few exceptions to this power-saving scheme for background apps that play music, print, receive instant messages or e-mail or VoIP calls, synchronize or share content, download or upload files, or refresh "live tiles." If the apps running in the background are "Metro-style apps," they can perform those operations concurrently with an active app. Windows 8 comes with an application programming interface (API) that lets developers enable background processing for Metro-style apps, if needed. Another exception is anti-malware applications, which may need to initiate a scan based on activity on the system.

Metro-style apps are written to take advantage of the new Windows Runtime environment introduced with the Windows 8 developer preview. They differ from so-called "desktop apps," or the classic menu-driven x86-based applications that are seen running on current Windows systems.

Microsoft typically claims that current (x86) applications capable of running on Windows 7 today will be able to run on Windows 8 when that OS is released. However, the claim neglects the nuance that Windows 8 is also being created to run on ARM-based silicon. It's likely that Windows 8 ARM devices won't support legacy x86 desktop apps, based on a comment made by Steven Sinofsky, president of the Windows and Windows Live Division. However, the x86 system-on-chip hardware being designed by AMD and Intel will support both legacy desktop apps and Metro-style apps. Microsoft announced the new system-on-chip support in January 2011 .

Windows 8 running on the new system-on-chip technologies will enable a "connected standby" mode, which allows the device to receive communications (such as e-mail and instant messages) while conserving battery power, according to Farag and Srour. A new element in Windows 8, called the "desktop activity moderator," will control the resource use of applications that operate in this connected standby mode.

ARM chips being developed for Windows 8 are system-on-chip processors, too. Based on that fact, and the language in the blog post by Farag and Srour, veteran Microsoft watcher Mary Jo Foley hypothesizes that Windows 8 on ARM will support running classic desktop apps. However, even if that turns out to be the case, developers would have the task of recompiling their x86 apps to run on ARM-based metal, which likely would be a daunting prospect.

Consequently, those Windows 7 users with legacy x86 apps who are thinking that they want to run them on the new Windows 8 ARM platforms will be disappointed.

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About the Author

Kurt Mackie is senior news producer for the 1105 Enterprise Computing Group.

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