What is Windows Service
Previously called an NT service, the core function of a Windows aervice is to run 
an application in the background. There are few things that make them different 
from a Windows application. [b]A Windows service starts much before any user logs 
in to the system[/b] (if it has been setup to start at boot up process). A Windows 
service can also be setup in such a way that it requires a user to start it manually 
– the ultimate customization! 

Windows services have their own processes, and hence run very efficiently. 
Normally a Windows service will not have a user interface for the simple reason 
that it can be run even if no one is logged into the system, but this is not a rule 
-- you can still have a Windows service with a user interface. 
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