Currently windows defaults to SimpleFSDirectory, but this is a problem due to the synchronization.
I have been benchmarking queries sequentially and was pretty surprised at how much faster
MMapDirectory is, for example for cases that do many seeks.
I think we should change the defaults for windows as such:
if (WINDOWS and UNMAP_SUPPORTED and 64-bit)
I think we should just consider doing this for 4.0 only and see how it goes.