Originally Posted by Entropy512
Android has supported emulated storage (where /data/media is mapped to /sdcard with a special FUSE daemon that makes /sdcard have DOS-like permissions despite an underlying ext4 partition) since ICS. It's pretty much the standard in all new devices - the Find 7 is to my knowledge the only device launched in 2014 not to use emulated storage. Most devices in 2013 also did - Oppos were again the rare exception.
As I understand it - for some reason Chinese users prefer the legacy pre-ICS partitioning scheme. My guess is due to UMS vs. MTP - MTP is required for access to emulated storage, UMS can't be used, but a lot of older desktop OSes have issues with MTP. So Oppo finds themselves in conflict between their home market (China) and expanding in the West. That said, the Find 7 was kind of a screwup in achieving this goal, since the internal sdcard partition was ext4 which meant UMS was a no-go for it.
I've got it now. Thanks for your explanations
I saw that Oppo phones didn't follow Android guidelines (yet?) by not using the emulated_storage mounting method but I didn't know why.
And your right, mtp doesn't work in Windows XP (or is hard to make working) and there's a lot of Asian people still using it. Obvious once you said it...
And that's also why only external sdcard is accessible in UMS mode in recovery.
Thanks again for your enlightenment. 😊