I was under the impression highmemfix was only for faster PC's.Yesterday I had my VC go to crap on the Lancair. I had been flying in PNW (taxes my system heavily) and then around Florida, about 3 hrs in total. It almost felt like a GPU OOM issue. Someone told me highmemfix is the trick. But what does it do and will it really help?

I was under the impression highmemfix was only for faster PC's.Yesterday I had my VC go to crap on the Lancair. I had been flying in PNW (taxes my system heavily) and then around Florida, about 3 hrs in total. It almost felt like a GPU OOM issue. Someone told me highmemfix is the trick. But what does it do and will it really help?

It looks like you have the invisible texture problem that highmemfix solves. To quote bojote from his post here http://forum.avsim.net/topic/280688-graphics-corruption-in-fsx-update-possible-solution-found/page__st__475:

You were very close :) It fixes a 'bug'... RTM and SP1 had a problem with D3DX (the effects component of DirectX, which also includes DirectX Audio btw) The problem, was that FSX (when using more than 2GB memory) crashed and/or corrupted graphics. The very first person to ever report this was 'Phil Taylor' in 2007, see here:http://blogs.msdn.co...ress-space.aspxLater, MS 'fixed' this bug in SP2, (The D3DX functions required a LARGEADDRESSWARE flag to be passed) and either it was NOT passed OR there was a BUG in the D3DX libraries not recognizing it. It seems that the problem was originally with D3DX as you can see after reading Phil post.In SP2, the correct flag is passed to the D3DX functions but ONLY if HIGHMEMFIX is set to 1. I can only assume that MS forgot to make HIGHMEMFIX a default value OR probably they did it on purpose because they didn't have the chance to test the effects of using HIGHMEMFIX when it was NOT needed (e.g 32-bit OSes running FSX without LARGEADDRESSAWARE flag set) and/or no 3G switch.This, is the particular function causing all the problems when HIGHMEMFIX is not set:http://msdn.microsof...y/bb172731.aspx

There is absolutely no reason to not have HIGHMEMFIX=1 in your cfg - it was supposed to be enabled by default in SP2 and actually is enabled by default in ESP builds that came after FSX SP2. That's info straight from the horse's mouth - it's supposed to be on by default.