Before windows incorporated burning into itself, I use to use 3rd party software to burn multisession ISOs (not UDF, which was always hit and miss). Most of the time, multisession worked, even between computers. In the cases where it didn't, I attributed it to incompatibility between all sorts of things that I can't recall now. I spent two evenings (and much more in the more distant past) reading up on the current Windows capability of burning discs. In recent times, web info indicates that Mastered format is ISO, while Live is UDF. I will be using discs to migrate info between Windows 7 machines, so I suspect (and hope) that there will be no compatibility issues. Though I don't know for sure until I try it. Perhaps the hardware itself can give rise to incompatibilities. In fact, I have no issue with using Mastered, since I burn discs so infrequently that I can afford to waste disc space in order to maximize compatibility. However, there is a confusion that I'm hoping to get clarification on if only in order to know what's going on. From what I've read, closing sessions applies to Live format and not Mastered. I find this odd, since I was able to work with multisession ISOs before Windows XP without resorting to UDF. Is this just because Microsoft decided not to support multisession ISOs? P.S. I am working only with data files, not audio/video media.