How do i tell if i have a lock up or non lock up trans?

Oklacarcollecto said
Lock up is the later 904 overdrive transmission. It would have been in the mid 80s and newer cars. I don't know the exact year it started.

70aarcuda said
first lock up was the converter..in 1978....

over drive with lock up converter in 80s

Thats what I was thinking it was as far as the converter.What is the benefit of the lock up over the non lock up.I don't mean to high jack but this lock up deal has been on my mind.