"Move to SD card" button is disabled. Why?

[James_Watson]

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?

 

[Jeffrey]

Most Apps are not designed to run from an SD Card. If the Dev knows his App will not run properly, he most likely disabled the button.

 

[FoxKat]

The other thing regarding moving apps to the SD card is that in some cases the developers can place portions of the application on the SD card, such as subroutines that need to be called into RAM infrequently. this means that the program itself isn't actually running from the SD card, but that lesser needed portions of the application are stored off of the main system memory to conserve system RAM. This isn't much different than the pagefiles area on Microsoft Windows.