How does OpenVMS VAX maintain system time?
VAX systems maintain an interval clock, and a hardware clock. The VAX hardware clock is called the TOY (“Time Of Year”) clock. The register associated with the clock is called the TODR (“Time Of Day Register”). 4-7 Time and Timekeeping The TOY clock-as used-stores time relative to January first of the current year, starting at at 00:00:00.00. It is a 100 Hz, 32-bit counter, incremented every 10ms, and thus has a capacity of circa 497 days. OpenVMS (on the VAX platform) stores system date information-and in particular, the current year-in the system image, SYS$SYSTEM:SYS.EXE. The TOY is used, in conjunction with the base date that is stored and retrieved from the system image, to initialize the interval clock value that is stored in EXE$GQ_SYSTIME. Once the interval clock is loaded into the running system as part of the system bootstrap, the system does not typically reference the TOY again, unless a SET TIME (with no parameters) is issued. The interval clock value is updated by a perio
