The turbo button came out of "turbo XT" PC clones, rather than being some sort of defined standard. Whether or not "turbo enabled" meant "runs at normal speed" or "runs at 4.77 mhz" was entirely dependent on how your case and motherboard happened to be wired, as there was no industry-wide standardization effort at that point. There's a great video on how PC clones evolved over time here if you're interested: https://www.youtube.com/watch?v=LGoM3Sqr2-w