i just want more control over my fan speeds like i did windows,with that said i used smc fan is it normal to see one option to change the fan speed in the system?i see others with imacs have 3 options etc
I THINK there's only a single (larger) fan on any of the newer iMacs, someone else may post back who can verify that. The larger fan would be able to move more air (more efficient cooling), and run slower for less noise on average.
The older iMacs usually have up to 3 fans.
So, yes, you would only see one choice for changing fan speed (only one fan)
Just my opinion - the cooling is pretty good on the iMacs when booted to OS X. I would suggest that you decide by actual results if the cooling is working well, or (by how you work) that you need to "help" your cooling to some extent (when you actually note that the temp sensors report temps that you perceive as "uncomfortable". I might do that with temps above 200F/95C.
(I think you will find, as most users report, that the iMac does a sweet job at temp control without any assistance from you.
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