We often use iTunes to backup our iPhones or iPads on computers. And when the hard drive where iTunes store backups is going to run out of space, we need to change iTunes backup location.

iTunes backup location on Mac:

~/Library/Application Support/MobileSync/Backup/

iTunes backup location on Windows XP:

\Documents and Settings\(username)\Application Data\Apple Computer\MobileSync\Backup\

iTunes backup location on Windows Vista, 7, 8, 10:

\Users\(username)\AppData\Roaming\Apple Computer\MobileSync\Backup\