We intend to move the multicore app out of beta on Monday the 29th August. This means that by default everyone will get both singlecore and multicore WU.<br />
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The main motivations for this are that multicore provides better CPU and memory efficiency, and we only have to manage a single stream of tasks instead of two.<br />
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If you do not want to run multicore you can disable it in your ATLAS@Home preferences in the option "Run only the selected applications"<br />
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By default the tasks will use as many cores as you have allocated to BOINC. For tuning the number of cores that the tasks will use you can create an app_config.xml file as described in <a href="http://atlasathome.cern.ch/forum_thread.php?id=517" rel="nofollow">this thread</a><br />
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At some point we plan to discontinue the singlecore app and run only multicore. The multicore app will also run on 1 core so you can still continue with ATLAS even with a single core.<br />
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Happy crunching!<br />
The ATLAS@Home team