I upgraded a TiVo Premiere XL to a 2TB drive (purchased with software already on it), but then had a perfectly good 1TB XL drive left over. I wondered if I could use the 1TB XL drive in a regular Premiere (without doing an image copy from the Premiere drive to the XL drive). I couldn't find a direct answer on the forums, but I knew there must be some difference in the images because upgrade drives are sold differently, depending on the model. Well, I purchased a "45 hour" Premiere at a good price and decided to give it a try. Before I ever started up the new box, I put the original 1TB drive from the XL in it. It started up but indicated there was a hardware issue. It appeared that it wasn't going to work, but I persisted. I did a "clear and delete everything", a guided setup, and several "connect to TiVo service" to get the latest software downloaded. Somewhere in the process it recognized it was a Premiere and not an XL and downloaded the appropriate software. I'm not sure what the difference is beyond the TiVo introductory cartoon (the XL starts with a THX logo). Anyway, it is now a fully functioning Premiere with 157 hours of HD recording capacity. The multi-room streaming between Premieres (the primary reason I wanted an additional Premiere) works great. So if anyone out there has an original Premiere XL drive left over after a capacity upgrade and has thought about putting it into a Premiere, go ahead. It will work fine after you "clear and delete", do a guided setup, and download new software.