- >1 A Bit Of History
- >2 The New Stuff
- >3 Why Talk About This Now?
- >4 The Consequences
- >5 Perhaps There’s A Plan
In recent years, Google hasn’t exactly been known as particularly hospitable toward SD cards with regard to its Android operating system. This theme is most often associated with the Nexus line of devices - the Nexus One was the only such handset to ever offer expandable storage. But despite arguments from Dan Morrill and Matias Duarte suggesting this stance is about keeping the Android interface simple and file picker-free, people still want more space. Google is apparently firming up its position on expandable storage even further, though, and in a way that limits flexibility and changes how we can use it.
A Bit Of History
Let’s start with just a little bit of terminology. Almost every type of storage in Android is considered "external storage," including the non-removable flash memory that comes in every device, which is designated "primary storage." Everything else is considered "secondary storage." Since the very early days of Android, an app simply had to request the WRITE_EXTERNAL_STORAGE permission to have access to any and all external storage.
Back in March 2011, almost 3 years ago, a small modification was made to the Android source code that would change how secondary storage mediums (SD cards) were mounted by the operating system. The commit message simply read, "Mount secondary external storage writable by AID_MEDIA_RW rather than AID_SDCARD_RW." The side-effect of this change was that applications would now have to belong to the media_rw group to modify the contents of an SD card. To gain access to this group, a permission called WRITE_MEDIA_STORAGE was added.
Source : http://www.androidpolice.com/2014/02/17/external-blues-google-has-brought-big-changes-to-sd-cards-in-kitkat-and-even-samsung-may-be-implementing-them/