If you want to specify an alternate source file, in the Alternate source file path box, specify a fully qualified path of a shared folder that contains the contents of the sourcessxs folder from the installation media. Or, specify a WIM file. To specify a WIM file as an alternative source file location, add the prefix WIM: to the path, and then add the index of the image that you want to use in the WIM file as a suffix. The following are examples of values that you can specify:
Path of a shared folder: \server_nameshareWin8sxs
Path of a WIM file, in which 3 represents the index of the image in which the feature files are found: WIM: \server_nameshareinstall.wim:3