The Turbo button worked wonders for Tetris. You start it with turbo turned on, so Tetris adjusts to the computer’s speed - but it only does this once, at startup. As soon as the blocks start falling, you turn the turbo off, and now your Tetris runs at half speed. I even managed, a few times, to roll over a score of 32,768 (ah, those signed integers).

AFAIK no first-party IBM PC ever had a turbo button, only clones, and my only personal recollection of pre-286 clones running significantly faster than 4.77 MHz were the Compaq Deskpro and AT&T PC 6300.

I don't know about the PC 6300 — I only ever used it to run Aldus PageMaker, which, running under Windows on an 8086, could use all the speed it could get — but the Deskpro had a keystroke combination to switch between native and compatible speeds rather than a button.

Hmm, maybe my memory is betraying me. I remember our first family computer was an XT and then later we had a 386. Maybe I'm misremembering and it was the 386 that had the turbo button or maybe the earlier one was a clone. My first own PC was a 486 as well that I built together with my dad. Good memories.