Nearly every automatic transmission pre-2000's was a basic double planetary gear system. Which means you got 3 gears. So normally you'd have a gear selector of 'park'-'reverse'-'neutral'-'drive'-'2'-'1' where 2 and 1 were the actual gears that you could force the transmission into for increased engine breaking (for going down mountains so you don't melt your brakes). Or sometimes for low traction, you could leave it in '2' which would make it harder to spin the tires.
After 1980, an 'overdrive' gear was added to most transmissions. "Overdrive" in this sense means that for one turn of the input shaft, the output shaft would turn slightly more than one.
After the early 2000's, we started to see the introduction of 3 and 4 planetary gear sets bringing the total gears anywhere from 6 to 9.
After 1980, an 'overdrive' gear was added to most transmissions. "Overdrive" in this sense means that for one turn of the input shaft, the output shaft would turn slightly more than one.
After the early 2000's, we started to see the introduction of 3 and 4 planetary gear sets bringing the total gears anywhere from 6 to 9.