Form Wikipedia：http://en.wikipedia.org/wiki/Windows_service
In Windows NT operating
systems, a Windows service is a computer program that operates
in the background.[1] It
is similar in concept to a Unix daemon.[1] A
Windows service must conform to the interface rules and protocols of the Service
Control Manager, the component responsible for managing Windows services.[2]
Windows services can be configured to start when the operating system is started and run in the background as long as Windows is running. Alternatively, they can be started manually or by an event. Windows NT operating systems include
numerous services which run in context of three user accounts: System, Network and
ServiceLocal Service. These Windows components are often associated with Host
Process for Windows Services. Because Windows services operate in the context of their own dedicated user accounts, they can operate when a user is not logged on.
Prior to Windows Vista, services installed as an "interactive service" could interact with Windows desktop and
show a graphical user interface. In Windows Vista, however, interactive services
are deprecated and may not operate properly, as a result of Windows
Service hardening.[3][4]