Originally posted by Louzer
One other thing I remember about 486's and their 'Mac-equivlents' at the time, the 68040 Centris models. The 68040 ran at 25MHz and 33MHz, while the 486's ran usually at 50 and 66. But, IIRC, I read that the 486's were speed-doubled at the clock rate (which would explain how a turbo button could work). The Macs also were doubled, but Apple didn't double the MHz when advertising (so, like, they both were really 25 and 33MHz chips doubled, just the Intel folks used the 'doubled' number and Apple didn't).
This is riddled with inaccuracies.
The i486-DX2 models had a processor clock speed that was twice the speed of memory bus. This is identical to modern 2.0 Ghz PowerMacs that have a 1.0 Ghz memory bus. Of course everyone calls the Mac a 2Ghz machine and not 1Ghz, just as with the Intel machines.
The 040 Macintosh models were not "clock doubled", although later on Apple marketing started lying and marketing the chips as "33/66Mhz" or similar. The lower number is the correct one for those machines, and their lack of real oomph was the big reason for the last Apple CPU shift.
The function of the Turbo button (when turned off) was to knock the clock speed down to 8Mhz, the same as a genuine IBM PC AT. This improved compatibility with software that used specific timing loops. By the 486 era, the Turbo button was just a fugly case feature that was rarely wired up.