I just ordered a new TiVo Premiere 4 from TiVo. From what I understand the Premiere 4 comes with a 500 gb drive but can only record 75 hours of HD programming. My current TiVo HD has a 500 gb drive (I installed this drive myself to increase recording time from 20 hours to 180) but has room to record @ 180 hours of HD programming. Anyone know why the difference? I ask this question because I just ordered a new Premiere 4 and planned to move the drive from my TiVo HD to the premiere? Also, will I be able to simply swap the TiVo Premiere 4's drive with the one from my TiVo Hd?