On my Samsung Galaxy Note 3 mobile phone, Settings - Application manager. In "App info" window of some apps, the "Move to SD card" button is grayed out. But for another apps, the button is enabled. So then, what does this difference result from? And I found that the app "Move to SD card" button of which is grayed out is not always a system app. For example, Amazon Appstore and some apps I got from this appstore. So, I am confused. Is there an option in manifest file for developers to build his/her app in order to enable or disable the button? Can we have a choice between SD card and device storage when we install an app?