Inside Windows 8: Jon Berry - Desktop Activity Moderator and Connected Standby

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Jon Berry, a veteran Windows engineer, digs into the new way Windows 8 manages processes to support the brave new world of Windows running on various CPU architectures including ARM and ATOM, which present an interesting set of technical challenges given the need to aggressively preserve energy when running—yet not fully running—while in a battery-powered state.

Jon owns the Desktop Activity Moderator (DAM), which, as the name implies, moderates desktop processes. The DAM is one of several new features in Windows 8 designed to ensure consistent, long battery life for devices that support connected standby.

Connected standby occurs when the device is powered on but the screen is turned off. In this power state, the system is technically always "on" (to support key scenarios like mail, VoIP, social networking, and instant messaging with Windows Store apps). It is analogous to the state a smart phone is in when the user presses the power button.  

As such, software (including apps and operating system software) must be well-behaved during connected standby. The DAM was created to suppress desktop app execution in a manner similar to the Sleep state. It does this by suspending or throttling desktop software processes across the system upon connected standby entry. This enables systems that support connected standby to deliver minimized resource usage and long, consistent battery life while enabling Windows Store apps to deliver the connected experiences they promise.

The DAM is a kernel mode driver that is loaded and initialized at system boot if the system supports connected standby. 

How does Windows 8 provide this always-on experience and not drain the battery in 10 minutes? What does the DAM actually do? How does it work? The DAM is part of a larger management system, which Jon also describes here. What is connected standby, exactly? Jon spends a lot of time at the whiteboard answering these and other questions. Thank you, Jon!

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    The Discussion

    • User profile image

      Charles, you asked a very interesting question near then end about what happens if you have a desktop app like Outlook which is periodically polling for mail and the system goes into connected standby. Jon gave a long answer which briefly mentioned virtualized timers and that a timer might fire 48 hours later than intended but didn't specifically answer the question.  Except maybe by implying it can't work that way anymore and apps that do that may do their poll very very late.  Is that the case? 

    • User profile image

      @paradyne - The short answer is yes, these classic pooling applications will have their time stretched (you can call that "very very late", relatively speaking).

      One the other hand, think about what happens on classic up-to-windows7 Standby (and also Windows 8 if the hardware does not support Connected Standby): When they do Standby, REALY nothing happens - everything just stops. In essence, Classical Applications on Connected Standby are no worse than they were before - maybe a little bit better.

    • User profile image

      What if I have a desktop application that may take a long time to finish like downloading an ISO either through a browser or BitTorrent, installing a very large piece of software, running some simulation, compiling, etc. Now, say I press the power button or the screen goes off after some time. Will those software be suspended?

    • User profile image

      Another question. Have they extensively tested virtualization software under Connected Standby? As a simple example, will the time in the virtualized OS gradually go off each time the host goes into Connected Standby?

    • User profile image
      If we wanted to test that our desktop, network-related services and processes work correctly with DAM, is there a laptop available that supports Connected Standby?

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