Python 2.7.8 (64bit) on Windows (64bit) is half as fast as 2.7.8 (64bit) on Ubuntu (64bit)

On Linux it takes 1.09171080828 secs.

On Windows it takes 2.14042000294 secs.

http://ift.tt/1BNQ6qV <-- code for the benchmark

I am aware that the GIL creates more or less single threaded scripts.

Windows box is my Hyper-V host but should be beefy enough to run a single threaded script at full bore. 12-cores 2.93Ghz Intel X5670s, 72GB ram, etc...

Ubuntu vm has 4-cores and 8GB of ram.

Both are running Python 2.7.8 64-bit.

Q: Why is windows half as fast?