Since the 30 hour unit I have has a 27 gig, I'd guess the 72 hour is somewhare in the 60 or 70 gig range. Probably pretty easy to find out by seeing what size Quantum makes in the size range, since they provide the drives for TiVo. By the way, for those of you with a 15 hour TiVo - TiVo now is offering an upgrade from 15 to 30 hours for $299 on their web site. Just send in your TiVo and they send it back with a bigger drive.