Where is my iPhone 4 backup stored in Windows 7?

iPhone Backup Location for Windows 7, XP, and Vista

Windows XP stores all of your iPhone backup files in this location:

C:\Documents and Settings\user\Application Data\Apple Computer\MobileSync\Backup

Windows Vista and Windows 7 backs up the iPhone files to here:

C:\Users\user\AppData\Roaming\Apple Computer\MobileSync\Backup

Obviously if your main drive is not C: then you’ll have to change that, same goes for ‘user’

Note to Windows users: the Application Data and AppData directories and their contents (iPhone backups included) are considered ‘hidden’ so you will need to enable ‘Show hidden files’ within Windows Explorer before you will be able to see the files.

http://osxdaily.com/2009/09/11/iphone-backup-location/

On Windows, is there a way to that I can specify a different location? (My C: drive is out of space, but D: has plenty!)

While an application is running, it may create some additional data, without which the program may not function properly. The stored data is for use by the program itself. The "Application Data" folder is the storage space for such data. To deliberately avoid user access, this folder is hidden by default.

This setting enables you to change the default location/path of the "Application Data" folder.

For this, go to Start > Run, enter "regedit" and search the keys listed below. You can create an expandable string value "AppData" in "User Shell Folders" key, if this value does not exist.

Now, double-click the Value Name "AppData" under "Shell Folders" and "User Shell Folders" keys respectively, to define a new path in their Value Data fields for your "Application Data" folder.

Refresh view of your computer for the changes to take effect.

NOTE:

After changing the path, you have to copy all your "Application Data" files from the old location to the new location. Then, you’ll have all your files for your applications at the new location. All subsequent data will be saved at the new location by default.

Source: http://www.tweaklibrary.com/System/Application-Path/71/Change-default-location-o f-the-%E2%80%9CApplication-Data%E2%80%9D-folder/10471/