In Windows the fan will be on except at temperatures at or below 31C. In addition, if BIOS is set to have fan always on with AC power, fan will always be on if AC power is plugged in. Whenever the fan transitions from off to on, it generally spins at the second to lowest speed (pretty dumb).
There are really two fan patches. The one that mac4mat did originally and the one I wrote late summer 2012.
mac4mat's version:
- makes no attempt to force the fan off
- at temps between 35C and 52C (inclusive), will hold the fan at its lowest speed
- at temps less than 32C or greater than 54C, will set the fan to "automatic" mode (Windows mode)
mine:
- my version forces control over the fan by making the EC think the CPU heatsink is 31C
- fan speed is loosely controlled by a DSDT table, FTAB
(default FTAB, from the patch)
Code:
// Fan Control Table (pairs of temp, fan control byte)\n
Name (FTAB, Buffer ()\n
{\n
50, 255, // 255 is off (really auto, but at low temp it is off)\n
57, 128, // 128 is slowest speed\n
63, 82,\n
68, 74,\n
72, 59,\n
75, 49,\n
0xFF, 0 // last entry must be 0xFF, 0 is max fan speed\n
})\n
Values in the first "column" are temperatures, values in the second column are fan control values/steps (correspond to speeds). CPU temps below or equal to the number in the first column cause fan to spin at the value specified by the second column. You would have to experiment to discover how each of these values correspond to RPM or read my fan thread... they were probably enumerated somewhere along the way. I don't recall how each of the seven fan control values correspond to fan RPM, but those are the only steps available. 255 is off (or "auto") and 0 is full blast.
I say "loosely controlled" by the FTAB, because changes to the fan speed are also moderated by using averages and timers that keep from having constant changes in fan speed.
Also, with any version, if you set BIOS to have fan always on with AC power connected, fan will never turn off as long as you are running on AC power.
Thus the only way to exercise absolute control over the fan is to uncheck the BIOS fan option, and use my DSDT based fan control solution, with a table to your liking.
There is more information in the fan thread.