What is the difference between R-12 and R-134 refrigerents?

I posted a similar answer in another area

Cars prior to 1994 used R-12, and after 1994 all cars were equipped with R-134A. The reasoning for this is because R-12 refrigerant is a CFCs (chloroflourocarbons) which depletes the ozone layer, whereas the more modern R-134A does not contain CFCs.