RTC(3) Library Functions Manual RTC(3)
rtc - real-time clock and non-volatile RAM
bind #r /dev
The rtc device supports the Mostek MK48T12-15 Zeropower/Timekeeper and
similar devices with real-time clocks and non-volatile RAM.
The rtc file behaves just like /dev/time (see cons(3)). The real-time
clock is maintained on-board; /dev/time is set from the file server.
Neither is necessarily more accurate.
The nvram file provides (if permission allows) access to the local non-
volatile RAM. For example, boot(8) reads the machine's key from there