Do the apps really move to the SD Card?

[Mackenzie Slater]

I brought the Tab for to read my comics and a couple of games. Most of the comic apps state they have been moved to the ext SD Card but once I downloaded the comics (Comixology), almost all the 16 gigs is taken on my device, not my card. I'm looking in to the folders and a lot of them are still on the internal storage, not the SD card like it states it is.

Samsung Tab 4 10.1
OS: 4.4.2

 

[Paul627g]

To my knowledge only a portion of the app is moved to the SD CARD. Some of the app still remains on the internal storage of the device.

 

[Rukbat]

Some apps can't run from the card at all (like system apps and widgets - and apps written with code that won't run from the card.

Some apps can be moved to the card, but won't run from it, because the "developer" isn't really a developer and didn't even check to see if his app will run properly from the card.

Of those few apps that can run properly from the card, the app is usually moved in parts. (Java apps are VERY seldom written from scratch - people use classes to do things. Why spend a week writing and debugging code that's already available and bug-free?) And basically, each class gets moved separately. For each piece that gets moved, there's a link in internal storage, pointing to the location of that code on the SD card. (Android looks in internal storage - it was never designed to run apps from the external card.) So if the app is written using enough small class files (not much larger than a link), "moving the app" to the SD card won't gain you very much space.

Three other disadvantages to moving apps to the SD card:

If you take that card and put it into another phone, the app isn't installed. Pieces of it are taking up space on the card, but it's not installed on the phone.

Copying that card won't copy the app. It's on the card, the space it takes is marked as "don't write here", but there's no "file" to copy, so unless you clone the card to another one of the same size (why would you do that?), you'll have to move the app back to the phone, put in the (probably larger - why else would you be changing cards) card and move the app to the new card.

Internal storage works more like an SSD. Writing is scattered around, so updating data doesn't write to the same spot all the time. That's how to kill solid state storage - there's a limited (huge, but limited) number of write cycles before something goes bad. An SD card is meant for long-term storage - write something to it and read it for years. Having an app on the card that writes its data to where it resides - IOW, to the SD card - will bring the card to end-of-life sooner than it should. And it's not that more expensive, or better, cards will last longer, it's that the technology works that way. The best card has a limited number of write cycles, and it's probably not much more than the worst card.

That's not to say you should never move an app to the card, just know what to expect when you do. (And back the app up to an apk file before you move it. [You should have backups of all your apps, including older versions - so when Google "improves" an app to death, you can install an earlier version that actually works - and so that you don't have to download an app to install it.] So if moving it messes it up, you can uninstall it, then install it again.)