Windows(C++) cross-compiles your code to C++, then compiles that to a binary. Windows(Krom) cross-compiles your code to JavaScript, then runs it in the Krom runtime which is basically Chakra. Krom is usually faster - this is typical for Haxe because the optimizations done by a JavaScript engine apply nicely to Haxe code and it’s true for Armory according to the numbers I’ve seen.