Starting with Android 3.2 apps write-ability to external SD card was restricted to only system apps (using WRITE_MEDIA_STORAGE permission). Also apps can make use of this content provider. So actual filesystem contents aren't visible over MTP, instead MediaStore (one of Android's built-in content providers) provides an indexed list of files. It means that sdcard partition or external SD card was not mounted as partition when connected to PC. But the primary intention was to retain a permission-less virtual filesystem (like FAT) over a permission-aware Linux filesystem (like ext4) so that data could be shared among apps (UIDs).Īndroid 3.1 switched USB Mass Storage (UMS) to Media Transfer Protocol (MTP). In Android 2.3 FUSE was introduced to emulate primary external storage ( /sdcard) over actual filesystem of sdcard partition which majorly remained vFAT. Since primary external storage was still smaller, apps continued to widely use secondary storage by placing files wherever they wanted, creating random directories on both storage. Now there were two external storage: primary ( sdcard partition) and secondary (external SD card).
So apps used to place a lot of data on external SD card.Īndroid enforced WRITE_EXTERNAL_STORAGE permission as early as in Android 1.5 to control which apps could write to external storage, so almost every app had to request this permission.Īs the internal flash memory grew in size, OEMs created a separate partition (usually named sdcard) "to provide external storage internally". As names suggest, private directories of every app (in /data/data/) aren't accessible to other apps, but data placed on shared storage is.Įxternal storage used to be physically external SD card (with permission-less filesystem from FAT family) in early days when flash storage was costly.
The reason is more historical than technical.Īndroid provides two types of storage to apps: private (or internal) and shared (or external). Apps usually don't write data to external SD card, but starting with Android 4.4 up to latest release 10, there is no permission to stop apps writing to Android directory on external storage.
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