PPM supports 5 task types: Fixed Units, Fixed Units - Effort Driven, Fixed Duration (the default), Fixed Duration - Effort Driven, and Fixed Work- Effort Driven.
Note: Task type may be displayed as a 5 option pick list (options above) or as a 3 option pick list (Fixed Units, Fixed Duration, Fixed Work), with a Effort Driven qualifier box. The task type is treated in the same way no matter how you set it.
A task's type determines which task property (duration, resource allocation units, or planned work) remains fixed when another property changes.
(click outside window to close)