It always blew my mind how well it worked on a 33 Mhz 486. I'm fairly sure it ran at 30 fps in 320x200. That gives it just over 17 clock cycles per pixel, and that doesn't even include time for game logic.

My memory could be wrong, though, but even if it required a 66 Mhz to reach 30 fps, that's still only 34 clocks per pixel on an architecture that required multiple clocks for a simple integer add instruction.