Posi Transaxle ?

Looking at possibly purchasing a second Boxster for DE use. It is a 2000 S. It has had 3 previous owners. Current owner doesn't know if it is a posi transaxle. We had the back end jacked up so I could do an underside inspection. I had him start it up and put it in gear. Both rear wheels turned in the same direction. I think this would indicate the it has a posi as my Mustang does the same. If this is true does that mean it is functioning or is there a better test to confirm it is in good working condition.

No, it does not have a limited slip (positraction) differential. I have an 01S, which has what Porsche call "traction control". The brakes are applied via computer control to the spinning rear wheel to equalize traction.

A simple test to confirm an LSD is to raise the rear of the car, engine off, in neutral. Spin one wheel by hand. The opposite wheel will spin in the same direction if the car has an LSD. If the other wheel spins in the opposite direction, you do not have an LSD.