The thread title may sound strange, but here comes the explanation and the question regarding which I would need some help. I recently purchased a 2.26 8-Core DP Mac Pro 2009, which came brand new. My plan was to exchange the CPUs and get a higher perfomance, but due to the substantially high price of Dual QPI-link CPUs I cannot afford now more than one. So I picked up a 6-Core 3.33 Ghz Westmere CPU (X5680) (along with all other tools needed because of the increased height of the new setup) and wanted to use it in a single configuration by leaving CPU Socket B empty and doing the upgrade with another X5680 later in the future. It has been clear for me that Dual Socket boards should boot up fine with only a single CPU, so I did a quick test: I simply removed the stock CPU from Socket B, and left the other one (2.26) intact. After carrying out the removal my Mac Pro booted up fine, but soon after the desktop appeared, fans started to spin up to max speed, causing me quite much of disappointment. Then I reinstalled CPU B and realized that if the screws of the heatsink are not tightened completely, the CPU is not recognized and the same phenomenon happens as before: machine boots up with 1 CPU running and fans spinning up after a while. So all this happens either because the female connector of the heatsink is not plugged in or because the row of power regulators are not touched by the slip of thermal pad at the bottom of heatsink. So could anybody help me in finding a workaround for this problem to work with only a single CPU for a prolonged period? I don't know if it could be a good idea to reinstall only the heatsink over the empty socket B to avoid such the spinning up of fans, what do you think about it? Also, one might say that a software-based fan control (like SMCFanControl) could solve the problem, but firstly, it is unclear for me whether the socket is really completely shut down and is it safe to leave the power regulators near the empty socket naked without any cooling and second, software is not a complete solution anyway (the whoosh would reemerge any time you would make a reinstall of Mac OS, for example, and neither do i know if it could be discarded when running Windows in bootcamp, which I will occasionally).