Of course! The crazy thing is that you could do it while the computer was running and it was mostly fine: DOS and many DOS games would just happily keep working, just at slighly different speeds. But then it wasn't uncommon for the PC to just freeze and then it needed a reboot.

But the best feature, to me, was those PC with a turbo button that also had a seven-segment display showing the current speed. This was looking really cool.

We added a variable frequency control to an IBM/AT and used it to adjust the CPU clock up to the point just below where the system would crash. Default was 6 MHz but we could push it up to around 10 MHz before it started crashing. That seemed amazingly fast at the time.

I distinctly rememver taking one apart and being very disappointed: the segment display was completely fake and showed 2 predefined numbers, not correlated to the CPU frequency at all.

Unless you set them correctly to actual CPU frequencies, in which case they correlated perfectly.

They were to slow the cpu down.

This is technically correct (the best kind…) however many people will have a different experience because it was sometimes inverted to be more intuitive.

Or Ctrl+Alt+- if your turbo button wasn't actually wired on the cheap XT clone...

My 486 had one.

At the time I had no idea what it was and...not sure I do now.

Great YouTube video on them! https://youtu.be/p2q02Bxtqds

It was mainly for games written for the older CPUs that used CPU timing for the main game event loop. Turning off "turbo" would reduce the clock frequency and slow the game down to a playable speed.