Windows Diagnostic Infrastructure (WDI) is a collection of diagnostic tools that can help find the source of many common disk, memory and network problems. In addition, it can warn you of impending failures so you can either react to fix them, or at least save your data while you can. The Diagnostic System Host works with Diagnostic Policy Service (DPS) as a component of WDI. If you don’t find any value in Vista’s diagnostic features you can disable this service, though any application that makes use of it may then not function correctly, and because this service is set to manual by default, there will be little benefit to disabling it.