I have a 2011 iMac with an i7 Sandy Bridge CPU which will thus run up to 8 BOINC tasks at a time. I'm currently also running another project (no chance of getting 8 tasks out of CPDN at the moment :-)), and I also have a Windows 7 virtual machine (using Parallels). I find that unless I limit the number of CPUs that BOINC can have, the computer runs like a dog. I currently have no of CPUs set to 50% (which means 4 virtual CPUs) in BOINC, and Windows has 1 - I don't know whether that means 1 physical core or 1 virtual one...). Anyone have any suggestions as to the optimum settings to use?

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Derrick Ashby

The i7-2600 has four cores with eight threads. Hyperthreading usually gives a small increase in total throughput (~10-20%). However, because the threads are not really independent cores, the models will run much more slowly - though more can be run. Clearly, more models will also thrash the rest of the system.

I now ignore the hyperthreading on any processors and set the number of CPUs in BOINC to make the real number of cores available. This is exactly what your CPU 50% setting is doing.