source:apple.com

Just yesterday Apple released a critical patch that fixes a major security flaw. That Mac OS update required 3GB free on my machine.  That’s trouble! I have an older MacBook Air with a 128GB hard drive so I’ve been hovering with under 2GB of available disk space for a long time.

Even after some aggressive spring cleaning of Applications and old file attachments I still did not have enough disk space for the Mac OS update. At this point it dawned on me that I had recently  used iTunes to setup a new iPad that I bought and all the apps autmatically synchronized onto the new iPad without downloading anything. All that data must be stored somewhere.

So, I had to find out where iTunes keeps its backups. A cursory Google search found Apple iOS Backups which reveals that iOS backup files are housed in ~/Application Support/MobileSync/Backup for Macs. Sure enough, my mobile backup folder had 4 subfolders hogging up 20GB(!) of disk space. Since we only have 2 iOS devices in the house it was clear that iTunes still had backups for an old iPhone 3GS that I had given to my mom.

The folders contain encrypted iOS backups so I didn’t know which folder corresponded to each of my devices. Consequently, you have to delete your unwanted iOS backups using iTunes. The instructions “Deleting a Backup in iTunes” show that you can delete backups in iTunes >Preferenes > Devices.

Clearing out the old iOS backups gave me back 10GB of hard drive space! I haven’t had this much free disk space since I bought this laptop 3 years ago.