The Windows 7 search indexer is a service that runs in the background to build a database of files on your system. This is used to perform fast file searches, but other applications such as MS Office, Windows Media Player and even the start menu quick search will rely on this service.
If you rarely perform searches or require very accurate searches you may want to disable the search index to save some system resources and hard drive activity. This is not recommended for most home users, although it is unlikely to cause any damage by doing so.
To disable or enable the service, run "services.msc" either direct from the start menu or via the run box (press Windows Key + R to access this). Once loaded, scroll down the services list, right click on Windows Search and then click Properties:
If you want to disable the search index, choose "disabled" from the startup type dropdown box. If you want to enable the index, choose "automatic (delayed start)":