Hi,
yes, Mach3 will run on a 64 bit OS and that will in turn will run a UC100 external motion controller.
Note that its not fair to call a UC100 a USB-parallel converter....it so much more than that although granted
it is what it appears to do. Inside the UC100 it has an FPGA which receives numeric motion data and generates
high quality pulse streams from that data. No USB-parallel can do that.
On Amazon, Ebay and the likes there are swags of Chinese fake UC100's......don't go there, they don't work like the real
thing. Buy direct from CNCDrive or their nominated distributor.
Craig