After creating our answer files, the question came about as to how Windows knows to use this answer file. Our deployments took off after a reboot without us designating an answer file. Windows setup will use an answer file either explicitly, or implicitly.
The explicit method of user an answer file is by running the following command from the installation media: Setup.exe /unattend:filename. This will launch windows setup and will take answers from your unattend.xml file that you created with Windows System Image Manager (Windows SIM).
Windows setup also has some implicit ways of recognizing that you have an answer file. Windows setup will automatically look for an answer file in the following locations:
4. Removable read/write media in order of drive letter, at the root of the drive.
5. Removable read-only media in order of drive letter, at the root of the drive.
6. windowsPE and offline Servicing passes:
• \Sources directory in a Windows distribution
All other passes: