Note Indexing Service is no longer supported as of Windows XP and is unavailable for use as of Windows 8. Instead, use Windows Search for client side search and Microsoft Search Server Express for server side search.
The W3SvcInstance entry identifies the instance of the WWW server whose virtual directories are indexed by the catalog.
|Range:||1 - 4294967295 (0xFFFFFFFF)|
The W3SvcInstance entry is effective only when the value of the IsIndexingW3Svc entry is set to one.
Different virtual servers are identified by different values of the W3SvcInstance entry. You can set those values by setting each individual Catalog subkey entry to override the main registry entry.
Build date: 9/10/2012