Well just to add my 2p to the mix - I changed to an Affinitymask=14 just this week as I was so fed up of frankly rubbish performance of FSX. This really was the last one I was prepared to do to make it usable.The difference has been incredible - SO much smoother, and with steady FPS of 25-40 all the time (whereas before it was stuttering like crazy and barely reaching 20FPS). Same quad core, same graphics card, same add ons. I've even been able to max out the AA and AF settings on my modest Radeon 4770 for the first time.I would STRONGLY recommend this to anyone who is fed up of FSX performance to anyone who hasn't tried it. On the face of it, it seems illogical to remove a core to make things better. But the amount it frees up for the OS, active sky, radar contact, etc etc. makes it all worthwhile.I'm actually happy with FSX for the first time ever, which is really saying something.

To clear up a fewe issues1 - I know that my priaffinty task maneger shows fsx is on cores 0123, but the affinity mask in fsx.cfg is et to 14 1110 = means fsx using cores 123 only.I found its best to set fsx affinity in cfg file and not in priaffinity.2- Priaffinty is powerfull but it only has control over user tasks, so you cant set the priority or affinity of most windows and systems tasks, you only have control over user tasks like fsx etc.3 - Checking temps, and individual core usage with affinity mask 14 while fsx running, you can actually see that core 0 is least used and has lowest temp.4 - i have tried fsx at affinity 7 = 0111 meaning fsx does not use core 3 and addons go on core 3. With this i get higher fps , but also more stutters.By the way HT is ofcourse off on my i7.But even though many agree affinity 14 works very well, the new information here is, it works even better if all your fsx addons are put on core 0 and set to lowest priority, while fsx is set to high priority, but not !!!real-time priority!!!

Interesting discussion!Forgive my ignorance, but surely the OS itself will not be limited to core 0?What's stopping Windows from using the other cores if it so fancies?I thought at least WinXP Pro/Windows Vista/Seven would make full use of multi-core processors?CheersDavid

Because the OS itself does not make heavy use of multi-core processors. It is the applications running on the OS that may be coded to do such.