Change the Location of Your iTunes Backups on Windows Vista or 7 (iPhone and iPad)

My first couple of google searches were for some setting or registry key that iTunes might use to tell it where to place these backups, but such a thing apparently doesn’t exist. By default on Windows 7, my iTunes backups were stored to “C:\Users\onelson\AppData\Roaming\Apple Computer\MobileSync\Backup”. Since there is apparently no way of changing this location in iTunes, we have to ask the operating system to do iTunes dirty work for us.
Fortunately, Windows has a way of doing this using a concept known as symbolic links (symlinks, or in M$ speak, NTFS Junctions). A symbolic link is similar to shortcut, but lower level. (Update: Based on some great comments from John and Jake, you can skip the first couple of steps and use the built in command mklink to create the symbolic links)
Unfortunately Windows doesn’t have a built in tool to create symlinks. Don’t worry, I promise I’ll help you through this:

1. So to begin, you need to download this free tool to create NTFS Junctions. (This is a tool provided by a Microsft engineer on Microsoft’s website ironically enough)
2. When you unzip that file, extract the junction.exe into the C:\Windows folder so that you can run in from anywhere.

1. Next up, you need to move all of your existing backup files to their new location. This could be secondary hard drive, or another partition, or even an external hard drive. Before we move the files, make sure iTunes is closed.
2. To move the files, open up a “My Computer” Window and type this into the address bar: “C:\Users\%username%\AppData\Roaming\Apple Computer\MobileSync” (without the quote of course) and press enter. This should take you into your iTunes MobileSync Folder where the Backup folder is located.
3. You need to right click on the Backup folder and select “Cut”.
4. Now navigate to where you’d like your backups to be located. For me, I wanted them on the D: drive in a folder I created called “iTunes Backup”. Paste the Backup folder to this location.
5. Next you need to open a command prompt. To do this, click on the Start button and type in “cmd” (again, no quotes) and then press enter. A black window should open up that looks like this.
6. Now for the easy part, creating the junction. All you need to do to create the junction is type in the word “mklink /J” then the path to where Windows stores the files, then the path to where you decided to place your backup. So for me, I typed in: mklink /J “C:\Users\onelson\AppData\Roaming\Apple Computer\MobileSync\Backup” “D:\iTunes Backup\Backup” (Note that there are quotes around both paths since both paths contain spaces, these quotes are required).
7. If everything worked correctly, the junction command should indicate that it created the junction

Now when you backup your iPod Touch, or iPhone, or iPad in iTunes, the backups will be stored to this new location. If the location is an external hard drive, make sure the hard drive is plugged in and powered on BEFORE you open iTunes. Also note that you can do this same process for other folders. I discovered that one of the other HUGE folders on my hard drive is related to iTunes also. The Mobile Applications folder is 5.4GB on my system since I have so many applications (and some real monsters like The Elements App. I moved this folder to another drive and freed up another 5.4 GB on my drive.
This is certainly an advanced technique, and you could really mess up your iTunes data if you do this wrong. If you are unsure of any of the steps above, please ask for help from someone better versed in Windows. If you find any ways that I might improve this guide to make it easier to understand, please leave a comment.

http://www.theiphoneguru.net/2010/12/30/change-itunes-backup-location/