The turbo button was always on, or it should be. you would turn it off to downgrade your pc to run at the speed of the original IBM PC in the mostly vain hope that whatever old game that was programmed for that exact speed would start to run right. It was slightly be fore my time(we had a 286 with the button, but I was to young to be curious about it) Would the pc take the speed change without problems or was it best to reboot? I sort of hate whatever marketing genius figured out to label it "Turbo" instead of "Slow" But they definitely earned their bonus.

The real weird one from that era was the 7 segment led MHz displays that were popular in the 386/486 era. It was weird because the the chips could not change speed in the first place. And I don't want to say every system was like this, but every one I ever saw was set by a set of static jumpers or a dip switch. When you upgraded your cpu you put the little sticker that came with it on the chassis and changed the jumpers, they served the same purpose.