Hi,
yes it is perfectly possible to run Mach3 on 64 bit OS's, what will NOT run is Machs parallel port, that requires 32bit Windows7 or earlier.
If you have a 64bit OS then you MUST have an external motion controller. Chinese made controllers seldom work as advertised and
have poor or non existent support. I suggest either a US or European made controller and not one of the Chinese fakes either.
Craig