I'm sure the poster will reply later, but in the meantime.. AFAIK for a Palm Vx there were a number of OS updates, three or four at least. It may even have gone on all the way up to the point when PalmOS 5 was introduced (which was for a completely different architecture - m68k->ARM, although OS5 runs OS4 apps through a just-in-time compiler, so in fact most Palm apps. are to this day still m68k apps! Runs on anything..)