An NT service is basically just a normal executable program that has a few hooks that the operating system can call to tell it to start, stop, pause, or continue. They are typically started as part of the bootup sequence and run whether or not anyone is logged on. They can be started or stopped through the Services applet in the Control Panel. Windows 95/98 supports a similar scheme. A service process can be started automatically at boot time (through the RunServices registry key) and can run across user logoffs.