Abstract: Disclosed is a microprocessor operating system having a program which includes a plurality of tasks requiring periodic execution by the system, and wherein each task is comprised of a plurality of associated subtasks. The system executes the tasks in a orderly fashion by: (A) providing a time variable which is periodically updated to represent a measurement of time; (B) setting the time variable to a predetermined time period during which a first task may be executed; (C) determining whether or not the predetermined time period has lapsed; (D) executing at least one of the subtasks of the first task if the predetermined time period has not lapsed, and then proceeding to step c; and (e) executing another portion of program if the predetermined time period has lapsed, and then proceeding to step c before executing another subtask associated with the first task.