as my assumption ,OS freeze the application but still allow application to update the hubhttp://www.engadget.com/2010/03/17/windows-phone-7-series-multitasking-the-real-deal/
We've definitely learned a ton about Windows Phone 7 Series here at MIX, but getting the full picture on multitasking has been difficult, since the OS isn't ready, no one has final hardware, and the emulator seems to behave differently than actual devices and Microsoft's descriptions. So let's set the record straight on multitasking: it's not going to happen, at least not in the traditional way. Not only have we directly confirmed this with Microsoft executives several times, but the developer sessions here are totally clear on the matter -- you don't tell 1000+ devs that they should expect their apps to be killed whenever the user switches away from them if you don't mean it. Now, that's not to say that the OS can't do multitasking: first-party apps like the Zune player and IE can run in the background, and third-party apps are actually left running in a suspended state (Microsoft calls it "dehydrated") as long as the system doesn't need any additional resources. If the user cycles back to an app, it's resumed ("rehydrated") and life continues merrily along, but if the user opens other apps and the system needs additional resources, the app is killed without any indication or remorse.
If that sounds familiar, it's because it's basically a single-tasking riff on Android and Windows Mobile 6, both of which also purport to intelligently manage multiple running applications like this, and both of which usually find themselves greatly improved with manual task managers. We'll have to see if Windows Phone 7 Series can do a better job once it ships -- we have a feeling it will -- and later down the line we'll see if Microsoft decides to extend multitasking to third-party apps. But for now, just know that you're not going to be running Pandora in the background while you do other tasks on a 7 Series device -- it is a question we have specifically asked, and the answer, unfortunately, is no.
