10: fsx.CFG – AffinityMask

For Multiple Core support in FSX, add the following command line in fsx.CFG file.   The setting is not shown by default.


Choice of <n> as follows:

For 2-core 4-thread CPU
15=1111 = ALL 4 cores
14=1110 = last 3 cores  (cores read from back to front)
7=0111 = first 3 cores
3=0011 = first 2 cores
1=0001 = first core

For 4-core 8-thread CPU
255=11111111 = ALL 8 cores
254=11111110 = last 7 cores
252=11111100 = last 6 cores
127=01111111 = first 7 cores
63=00111111 = first 6 cores

For 6-core 12-thread CPU
4095=111111111111 = ALL 12 cores
4094=111111111110 = last 11 cores
4092=111111111100 = last 10 cores

Other core settings could be calculated from corresponding binary numbers to decimal numbers as shown above, or via the Affinity Mask Calculator on top of the page.   There is no need to use additional software such as Multicore Environment to achieve what is needed.

19 thoughts on “10: fsx.CFG – AffinityMask

  1. there is a neat calculator for the affinitymask value on the Gatwick Flight Simulation Group website which is an essence a neat binary converter, but it makes it easy for anyone to calculate. Just select the number of cores your processor has and if hyperthreading is enabled or not, and it will spit out both the binary and decimal numbers you need.


  2. Little question;
    in some tweaks i read the [JOBSHEDULER] lines must be at the last lines in the cfg file. Is this correct or has this no sense ?


  3. Tom, I just have to through this in for some of your I7-2600k users. On my system running at 4.6Ghz, capable of running stable at 4.8 but I am a little conservative, I run AffinityMask at 14 with HyperThreading turned off in the BIOS. This seems to balance all 4 of my cores at close to 100% when running FSX in flight according to Core Temp 1.0 on my G15 applet.

    Again it may not be the ticket for everyone.

    Rick S.


  4. Hi Tom, I stumbled on this post as I was looking at whether a 16bit number could be used for affinity masking a 6 core HT enabled CPU (3930k) as I’ve only ever seen the affinity mask as an 8 bit number for 4 core i7’s. I just wanted to know if you have confirmed that the masks you give for a 12 threaded processor work.

    Also readers may find my post here interesting – http://www.flightsimworld.com/forums/topic/202278-my-affinity-mask-testing-for-best-usage-of-cpu-cores-hyperthreading/

    On testing my overclocked i7 system I found hyperthreading to be detremental to FSX performance and the use of more than 2 cores unnecesary and possibly detremental to performance. Which just goes to show the importance of testing these tweaks on your own system.



    1. Hi Paul,
      I found many posts saying hyperthreading is detremental and you confirmed it on your system. But I find it works ok on mine.
      Every system varies and all you can tell whether a tweak works for you is to test it yourself. The posts on my blog are describing what I am using and how they perform on my system.
      They could be a reference and starting point for other simmers but not necessarily the best fit. Do test it.
      Same to affinity mask. I don’t use it now.


  5. Tom,
    Thanks for your affinitymask settings info.

    ” you should test different settings for the best result you are happy with.”

    I have i7 CPU X980@3.33 GHz with GTX480 card and Windows7 64bit

    I tried 62/64/255/384 and other settings, never find most sutiablet settings. I will try 4095. What are the other settings I should try if 4095 did not make any difference


    1. Hi Sanal,
      I can’t give you an easy answer. You do need to test different CPU combinations by yourself I am afraid. That’s what I did to find out the optimum setting, as you can see from my various fsx.CFG posted in different times.
      980 is high-performance 6 cores. You may consider running it without using the affinitymask.
      I used the affinitymask in the beginning. But I don’t use it anymore after I swapped to my current 6970 many months ago.
      BTW, hyper-threading is aother issue you have to explore whether turning ON or OFF is better to your system. Many people on the internet said disabling it brings better performance. It’s the opposite in my case.


  6. Wow man.. this site is like eating cookies.. can’t get enough.. hahahaha, so you what you are saying is after the affinitymask=4095=111111111111

    is this correct


    1. No, Dwayne. I just showed different affinitymask settings. To find the most suitable one still requires your own expedition since our hardware and software are different. For example, in my previous setup with 5870 card, Affinitymask=13 returned some good result. But my current 6970 doesn’t require it at all. So you have to try different options yourselves. My settings are just a reference — not a must.


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