Windows 8 blog talks about power efficiency for apps

The Windows 8 Consumer Preview is just weeks away from being released to the world, and one of the biggest concerns about any operating system, is how it will handle energy consumption.

Microsoft has written in the past about how Windows 8 will be more efficient in terms of battery life. In the latest post on the official Windows 8 blog site, Microsoft's Sharif Farag and Ben Srour write about how Windows 8 will improve the energy efficiency in the OS's applications.

In the blog post, Farag and Srour write:

For Windows 8, we started off with a rule that would apply to the large majority of Metro style apps:  if an app is not on screen, and the screen is not on, it should not impact your battery life. That doesn’t mean WinRT and the user model preclude multi-tasking. There’s a new way of thinking about how and when code takes into account modern hardware capabilities, networking demands, form factors, and reliability/security/privacy. There are going to be some exceptions (e.g. background email syncing, desktop tools), but for the majority of cases, we expect the app to do most of its work while you are actively interacting with it. When an app is not in the foreground, we wanted to ensure that it would either suspend completely, or use limited resources based on a set of common background capabilities (like copying files), which the app can access.

If a Windows 8 Metro app is running in the foreground, it uses a PC's CPU, memory, hard drive, and more just like previous applications for older Windows operating systems. However, app developers can also use Windows 8's new Background Tasks infrastructure. Farag and Srour state that Windows 8 will allow more apps to run via Background Tasks when a PC is plugged into a power outlet. The blog says that this will allow for better battery life because apps will only run when they are really needed.

Windows 8 Metro apps can also suspend apps in the background.  The blog post states that means " ... that the Windows scheduler (the component that schedules CPU access for processes and threads) does not include it in the CPU scheduling. Since the operating system is not scheduling the app, the app is not using the CPU, and it is possible for the CPU to drop into lower power states."

Farag and Srour also state:

The great thing about this new suspended state for your apps is that they are instantly ready for you to get back to them. When you switch to a suspended app, it resumes instantaneously and takes you back to exactly where you left off. With this, you will be able to switch between more apps faster than you ever have before on Windows. You’ll no longer need to care how many apps are running on your PC—with the help of live tiles keeping you informed about what is going in your apps, and the ability for apps to save and restore state, great apps always look like they are running.

Windows 8 won't allow any battery drain or performance issues on a PC even if a PC has a number of suspended apps. However, the upcoming Consumer Preview version of Windows 8 will allow people to close apps if they choose via the Task Manager.

Finally, Windows 8 Metro apps will also be able to handle background tasks. That includes things like downloading a file, playing music, or receiving emails and instant messages.  Microsoft has created a number of scenarios based on the types of applications and what they would do in the background. For example, Windows 8 can still print documents even though the printing app may have moved to the background.

If a Windows 8 laptop PC goes into sleep mode, both regular and Metro apps will be suspended which, of course, extends a laptop's battery life. However, some PCs are rarely turned off. In this case, these special kinds of PCs go into a low energy mode called "connected standby." Farag and Srour state that for those PCs, Windows 8 has a new feature, the “Desktop Activity Moderator." This new feature will suspend all of a PC's desktop apps when it goes into the low powered mode. When such a PC is brought out of its connected standby mode, the apps will resume their activities as if they were brought out of a regular PC's sleep mode.

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