Services start when the operating system begins. They run in the background, unobstrusively doing many of the tasks needed to keep the computer running smoothly.
Typical services include handling Input and Output (I/O) such as the printer queues or networked devices, automated updates, Bluetooth and wireless networked devices.
Developers can write their own services though this is harder than creating non service applications and debugging services presents unique challenges; a service is running all of the time, even before a user has logged in and/or after they have logged out.

