Aporte original por: remacberlin ,
The latest iMacs use the sensors inside the HD itself. If you fit a different model or make the sensor can't be read and the fans go on full speed. From 2009 on Apple used the internal sensors. You could still work around the problem by using the exact same model of HD. This year (2011) things got much worse - Apple uses HDs with a proprearitary firmware that uses 7 instead of 4 pins (they actually use non standart SATA connectors) on the SATA bus for themp reading. You therefor can only use Apple branded drives for a premium pricetag. More information [http://blog.macsales.com/10146-apple-further-restricts-upgrade-options-on-new-imacs|here]. Shame on Apple - lets work on a solution!