What is the PC’s Real Time Clock?
Every IBM PC compatible computer features a battery-backed “Real Time Clock (RTC)” chip. This contains a 32768 Hz crystal oscillator that drives a date/time counter. It also contains 114 bytes of battery-backed CMOS RAM that are reserved for BIOS use. The chip typically used is compatible to the Dallas Semiconductor DS1287 and Motorola MC146818B RTCs. How does MS-DOS relate to this? The original IBM PC was released with the first Microsoft DOS and Basic versions in the early 1980s. At that time, the engineers involved did not consider modern issues such as networking across time zones, mobile computing, automatic clock synchronisation, automatic daylight saving time updates, 24/7 database server operation, dual-boot installations, virtual-machine servers, etc. Microsoft and IBM established at the time the (now highly problematic) convention to keep the RTC adjusted to whatever the PC’s user considers her local time zone. MS-DOS never had any notion of Universal Time or any time zone ot
