According to a Microsoft blog last week, power management is getting a lot of focus in the next version of Windows, described as ‘an area of significant innovation for Windows 8 PCs’. Current levels of power management will continue to be available on x86-based PCs and there has also been work done on improving the power consumption of existing desktop apps. But there will also be new apps written to WinRT (Windows RunTime – Microsoft’s new programming model) that run on a new generation of hardware that supports new power management capabilities.
WinRT is behind the new Metro-style apps - full screen apps tailored to users', devices, touch interaction and the Windows user interface. Windows 8 is aimed at crossing both the mobile and desktop worlds through the Metro interface, with apps optimised for the environment.
As the blog points out, one new aspect of power management is to reduce the power usage of running apps. Applications inevitably impact power consumption through their use of CPU, memory and disk, so Windows 8 has adopted the rule, applicable to the large majority of Metro style apps, that if an application is not on screen then it should not impact the battery life. It doesn’t preclude multi-tasking, but does take into account modern hardware capabilities, networking demands, form factors and so on. So there will be exceptions, but in general an application will do most of its work while you actively interact with it.
When an app is not in the foreground it will either be suspended completely, or use limited resources based on a set of common background capabilities (like copying files), which the app can access. For example, it won’t get suspended if you start a copy job and then do something else while it completes in the background.
Suspension of inactive apps only applies to Metro style apps, and even then the most common tasks needed to be done in the background are enabled, including:
- Playing music
- Downloading a file from or uploading it to a website
- Keeping live tiles alive with fresh content
- Receiving a VoIP call
- Receiving an instant message
- Receiving an email
- Sharing content (like uploading photos to Facebook)
- Synchronizing content with a tethered device (like syncing photos)
Otherwise, after you launch an app and then switch away from it the operating system suspends it. It means that the app is not using the CPU, so it’s possible for the CPU to drop into a lower power state, an essential part of power saving. The app can be instantly resumed from the suspended state, taking you back to where you left off. It means that switching between apps is faster than was previously possible in Windows, and also that it doesn’t matter how many apps are running.
There’s clearly a lot of thought going into Windows power management (and the above is a summary of one part) – Microsoft describes it as an area of Windows that has been ‘reimagined for new scenarios’. Those new scenarios include the variety of devices that the operating system will run on, including more mobile, battery-dependent devices, hence the need to save power.
In fact the increasing use of mobile devices and their need to minimise battery use is a driver for greater PC power management in general. Different chips, alternative architectures and software that makes effective use of multi-core processing are all crossing over from mobile devices to mainstream computing. Making the applications more power-aware is going to be an essential part of PC desktop power management in the future.