Win 97 but it's only free for 30 days, then you have to pay the 30 dollars for registration but it's well worth it, I downloaded a bunch of frequencies during the first 30 days. I ended up getting the Win96 too for my Pro 96 as well. It's very user friendly and makes programming a snap. I might add it's also worth it to become a premium member on this site as well because you get to download the frequencies from RR to the Win program and transfer it to your radio.