I have found Windows a bit slower but never to the extent the author suggests. But then I have generally tested on clean systems without antivirus. So I suspect that this is a huge factor, esp. because it intercepts all FS calls and checks them. That's really not what you want when compiling code.

This.

And anything else you can find that registers with the kernel for file system calls. Logging mechanisms, etc. Anything the kernel has to talk to about file i/o is going to slow it down.