9 Dec
2021
9 Dec
'21
5:34 a.m.
On Thu, Dec 9, 2021 at 11:56 AM Tony Nicholson <tony.nicholson at computer.org>
wrote:
[snip]
Te old VAX-11/780 TOY clock didn't store the year. Instead it was stored
and loaded from the system disk file system (one of the files in [000000] -
I can't remember the exact details). Every year in January we had to do a
"SET TIME" command to update it.
I remembered there's the following entry in the OpenVMS FAQ -
"4.1.1.3 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 standalone BACKUP
explicitly prompt for the time during bootstrap, and why the time value can
"get weird" if the system crashes outside the 497 day window (if no SET
TIME was issued to update the saved values), and why the time value can
"get weird" if a different SYS$SYSTEM:SYS.EXE is used (alternate system
disk, standalone BACKUP, etc)."
There's many more hints in the FAQ. To refresh your brain cells see
Stephen Hoffman's website for a PDF file at
http://www.hoffmanlabs.com/vmsfaq/vmsfaq.pdf
Tony