19: Less CPU Core is More FPS

If allocating more CPU cores to FSX will bring higher frame-rates sounds logical,  the findings from recent experiments show a different result.

By applying different numbers to the AffinityMask command in fsx.CFG file, frame-rates achieved vary significantly.  And most important, allocating more cores to FSX (including default setting without AffinityMask) doesn’t necessarily mean that framerate will be subsequently higher.

My CPU is an i7 930.  After many testings, setting AffinityMask to:

AffinityMask=20 (00010100; two cores) generates the highest framerate

AffinityMask=84 (01010100; three cores) generates the second best FPS performance

However, setting to use fewer CPU cores will lengthen the time to load all FSX session, especially when a system has installed many complicated add-ons.

Above finding is true as long as no Saitek panels are used.

  1. When Saitek panels and switches are linked, AffinityMask=13 offers the best FPS performance
  2. When no Saitek panel is attached, AffinityMask=20 performs the best

Note: Above results are based on HD5870 card.

2 thoughts on “19: Less CPU Core is More FPS

  1. Often wondered about that, Tom. I have an AMD Phenom 550 dual core and never bothered with an Affinity mask thinking that both cores would be used by default, and no manner of mask would improve matters.


    1. Dual core is effectively supported by FSX without the need of Affinity Mask. For Quadcore and above, the parameter many times helps to achieve the best from CPUs. Also, in my experience, variation in graphics card may return a different result. Currently I don’t use AffinityMask but it was quite an effective parameter with my previous cards. No matter what, testing it on one’s system for the best performance is the only way.


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