There's the XT RTC, which has an (updated on rollover, software-set only?) year byte, while the AT docs say that it has a century byte? But some documentation I've found says it doesn't update? What happens on the AT and Compaq Deskpro 386 when the year byte of the RTC rolls over? And what about the XT? Should the XT RTC ignore the year? And then(in the XT-RTC case), what happens to leap years?