Why does VAX need a SET TIME at least once a year?
Because the VAX Time Of Year (TOY) has a resolution of 497 days, the VAX system time is stored using both the TOY and the OpenVMS VAX system image SYS.EXE. Because of the use of the combination of the TOY and SYS.EXE, you need to issue a SET TIME command (with the time parameter specified) at least once between January 1st and about April 11th of each year, and whenever you change system images (due to booting another OpenVMS VAX system, booting the standalone BACKUP image, an ECO that replaces SYS.EXE, etc). The SET TIME command (with the current time as a parameter) is automatically issued during various standard OpenVMS procedures such as SHUTDOWN, and it can also obviously be issued directly by a suitably privileged user. Issuing the SET TIME command (with a parameter) resets the value stored in the TOY, and (if necessary) also updates the portion of the time (the current year) saved in the SYS.EXE system image. This VAX TOY limit is the reason why OpenVMS VAX installation kits and
