conditions, most OSs can update the RTC date while the system is running.This behavior applies both to standalone PCs and PC-based network servers. In contrast, networked PCs can behave somewhat differently, depending upon the NOS. Many NOSs are configured so that when a PC logs in to the network, the local OS initialize the current date from the NOS so that the server controls the system date on its attached networked PCs.The system date is maintained correctly as long as the RTC is able to automatically update to the correct date or the OS has an opportunity to update it. However, the century rollover challenges this process because, under certain conditions, the PC RTC will not be updated correctly to the year 2000. This is due to an inherent flaw in most RTCs dating back to the early days of the PC, as well as peculiarities in the system dates of the most common OSs.When IBM first designed the IBM AT, they included an RTC so the user would not have to enter the date every time the system was booted, as was required in most PCs of that era. The user would enter the date and time once during the system installation using a custom setup program, and the RTC would then maintain the time and date, even while the computer was turned off. The original design of the RTC still prevails. The RTC device includes native support for only a 2-digit year field stored in a 1-byte register; therefore, only the lower 2 digits of the year are maintained automatically. The RTC stores the data describing the century elsewhere in on bye (the century byte) of nonvolatile storage. The century byte is not part of the core functionality of the clock feature and is not automatically updated when a century rollover occurs. Furthermore, as more of the RTC and nonvolatile storage functions have been folded into optimized chip sets, additional data reduction has been applied to further simplify the information. For example, some chip sets would use o...
