Which directory does Mac OS X 10.10.x keep iPhone back up file？ I backed up my old iPhone 5S with iTunes on Mac OS X 10.10，But It seems that it's not easy to find the folder. (In Windows，It's C:\Users\Administrator\AppData\Roaming\Apple Computer\MobileSync\backup)
Here is what you are looking for. 

    ~/Library/Application Support/MobileSync/Backup/