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When I moved an app to the Storage Card on my HTC One V, I found some data moved to USB Storage App. The Storage Card is still showing not used. What's "USB storage app"? Why apps are not moving into the Storage Card, instead moving into the "USB storage app"?

Before moving the app to the storage card Before moving the app to the storage card

After moving the app to the storage card After moving the app to the storage card

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Can you clarify what you mean by "The Storage Card is still showing not used"? Are there no files on it? If it's Android showing no used space, have you tried rebooting? –  Matthew Read Oct 31 '12 at 4:56
2  
I uploaded two screenshots to clarify it. –  Debiprasad Oct 31 '12 at 5:56

4 Answers 4

I guess you have to read the "USB Storage App" as the USB storage used by the app itself. So the code of the application.

If your application would for instance start generating cache information, saved pictures etcetera. And if it would save that information on your Storage Card, then the information will be showed under Storage Card.

So under "App" and "Storage Card App" is only the information and code of the application itself, not the information or data it generates. So in most case these 2 numbers will not change over time. And then under "Data" and "Storage Card" information generated by the application can be found. Either on the Storage Card or the internal memory (depending on the application I guess). This is the information managed by the application (local databases etc), so this will probably change over time, depending on the application in question of course.

This is my interpretation of those 4 terms. And if I check for some applications I use, it looks like my interpretation is correct. It is certainly correct for the applications I created myself, so for these apps I know where what information is saved on the phone.

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This is an excellent answer you gave. I think the user should accept this answer. The only part that puzzles me is why after moving the application from USB storage (internal memory) to SD card (external SD card), some of the code still remains under App (the code part of the application on internal storage). Is there some reason why some of the code could not be moved? Thanks. –  John Sonderson Dec 6 at 23:52
    
@JohnSonderson I don't really know, but my guess would be that it is because you still need some kind of pointer to the external app part. So maybe the main class of the application remains and points to the other part of the application on the external storage. That way the internal workings of Android stay the same (they can just list all the applications on the internal file system), but some of the code is placed externally. –  ndsmyter Dec 8 at 8:12
    
I have given it a second thought. Perhaps your interpretation is not entirely correct. Please see my answer below. –  John Sonderson Dec 8 at 13:40

The answer posted by @ndsmyter seems almost correct. The applications under Application manager -> SD CARD are those applications which can, at least in part, be moved to the SD card (and this happens where the checkbox next to the application's entry is checked). At first sight it may seem like "Application" and "SD card app" are for code on internal storage and on external storage, respectively, whereas "Data" and "SD card data" are for application data generated by the application on internal storage, and external storage, respectively.

However, upon further inspection I realized that on my Samsung Galaxy SIII I don't have an external SD card inserted, and despite this, while none of the applications listed under Application manager -> SD CARD have the SD card app field displaying anything but 0.00B, the example below, and many others, shows that SD card data is nonzero even though I don't have an SD card (click the image to enlarge):

Storage Space Breakdown

So, the only thing I am able to conclude is that these values are not the number of bytes taken up by the application and its data on internal and external storage, but rather how the data would be distributed among these four locations should the user decide to transfer the application to the external SD card (and some portions would still need to reside on internal storage for technical reasons).

Also note that on my device the field names are different. What on the original poster's post is called USB storage app on my system is called SD card app, very confusing.

enter image description here

And just as confusing is the fact that when I change the UI language to Italian, what in English was called "SD card app" now becomes "SD card applications" (applications: plural), which means not even the people that localized the system could figure out what these fields represented.

Regards.

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I don't think that because you have no external SD card, you don't have and external partition on your phone. Most phones use different partitions to seperate access to different parts on the system (that's the case on my phone). They are probably just talking about "SD Card" in case you do have an external SD card. The conclusion you've made is almost the same as mine, but how you get there doesn't seem completely correct to me. But it is indeed very confusing :-) –  ndsmyter Dec 8 at 14:30
    
@ndsmyter, on my phone internal memory, referred to as USB storage in the user interface, is mounted on /mnt/sdcard (symlinked /sdcard), and there is also a /mnt/extSdCard directory which is empty, and I think is where the SD card would get mounted if I were to get mounted. Perhaps external SD card counts as USB storage as well, hence the field USB storage in the UI in the OP's post. There seem to be inconsistencies regarding how these fields are labeled across devices. –  John Sonderson Dec 8 at 14:42

"USB storage" is the "internal" SD card i.e. the partition on the phone's internal memory that is treated like an SD card for general data storage.

"Storage card" is your actual physical microSD card.

The latter is where the stuff moved via "move to SD" or "move to storage card" gets put.

As for why it does this, Android's system for storing app stuff in user storage hasn't caught up with the concept of having more than one section of user storage.

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@JohnSonderson - Are you sure your suggested edit is correct? The last time I had a device running ICS, the "move to SD" function moved the app to the internal "SD card" partition, not to the actual SD card, as my answer currently states. Is your edit reflecting the status of ICS (which this question is about) or a later version of Android? –  Compro01 Dec 8 at 21:12

It seems to be the .android_secure folder on your SD card.

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So "USB storage app" presumably manages encrypted/protected apps on the SD card? Is there a way to have unprotected apps on the SD card? –  Matthew Read Oct 31 '12 at 15:14

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