1. A computer apparatus, said computer apparatus comprising, a plurality of processors, including a first processor subset of said plurality of processors, said first processor subset containing at least one processor, said first processor subset having a first memory associated therewith, and a second processor subset of said plurality of processors, said second processor subset containing at least one processor, said second processor subset having a second memory associated therewith, said first and second processor subsets being disjoint; an operating system mechanism which supports concurrent execution of a plurality of jobs, a first job of said plurality of jobs having at least one respective thread, a second job of said plurality of jobs having plurality respective threads; a grouping mechanism that groups said at least one respective thread of said first job and at least one thread of said plurality respective threads of said second job thread into a respective first group of a plurality of groups, said at least one respective thread of said first job and said at least one thread of plurality respective threads of said second job being grouped independently of their association with said first job and said second job, each said first group having an affinity with a respective said first processor subset and said first group being used to provide said first processor subset affinity for said at least one respective thread of said first job and said at least one thread of plurality respective threads of said second job contained therein, wherein said first group of said plurality of groups contains said at least one respective thread of said first job and said at least one thread of plurality respective threads of said second job, and said first group contains fewer than all said threads of said first job and said second job; and an affinity changing mechanism which alters said first group from said first processor subset affinity to a respective altered processor subset, wherein said at least one respective thread of said first job and said at least one thread of plurality respective threads of said second job of said first group are preferentially dispatched to processors of said first processor subset affinity before said altering said first groups is performed, and said at least one respective thread of said first job and said at least one thread of plurality respective threads of said second job of said first group are preferentially dispatched to processors of said respective altered processor subset after altering said first groups is performed.