-// This is a pretty hard core default - the number of processors in the box - 1
-$iInstances = isset($aCMDResult['threads'])?$aCMDResult['threads']:(getProcessorCount()-1);
+// by default, use all but one processor, but never more than 15.
+$iInstances = isset($aCMDResult['threads'])?$aCMDResult['threads']:(min(16,getProcessorCount())-1);