some clarification on PWM and PPM

I know that similar question have been asked in the past, and rest assured that I have read them. I know the basic difference between PWM and PPM. I am still a little confused though. Correct me if I am wrong, but:

-almost all hobby servos and R/C stuff expect PPM -the Servo library and the megaservo library both put out PPM -analowrite() puts out PWM

Is this right?


What sometimes confuses the topic is that a PWM output can be generated to simulate a PPM signal by adjusting it's base frequency to a 20msec period and vary the duty cyle for a 1-2msec positive pulse. Not something you can do with a simple analogwrite statement but by manipulating the timer it can be made to work somewhat.