• At boot time
• Automatically
• By a user with the Service Control Manager
• By a Win32-based application that uses the service-related Win32 APIs

Process-tree viewers under NT/2K/XP that show process owners will show all Services running under services.exe. All applications started by the user or other applications will be shown as running under explorer.exe.

The Service Control subsystem and the associated Win32 APIs are not supported in Windows 95/98/ME. In place of services, Windows 95 has two registry keys that allow users to run applications before a user logs in when the system first starts up. These registry keys are:
 HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunServices
 HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunServicesOnce
Values under the key RunServicesOnce are deleted after the application is launched.