Source Resiliency: Applications that rely on network resources for installation-on-demand are susceptible to source failures if the source location should change for any reason or become damaged.
The Microsoft® Windows® Installer provides source resiliency for features that are installed on-demand by using a source list.
The source list contains the locations searched by the installer for installation packages. The entries in this list can be
1) Network locations
2) Uniform Resource Locators (URLs),
3) Compact discs.
If one of these sources fails, the installer can quickly and seamlessly try the next.