[HECnet] US DST

[Johnny Billquist]

On 2020-03-08 22:28, Thomas DeBellis wrote:
> The recent post about multi-threaded NNTP for VMS (whaaay cool) jogged 
> my memory about something I had been wondering about.  This morning, a 
> large number of clocks got switched ahead an hour in the United States. 
> Tops-20 did it 'relatively flawlessly' as it has done so since the early 
> 1980's.  Back then, a lot of systems didn't.  None of our IBM systems did.

Hehe... Always a problem...

> A lot of that has changed nowadays with NTP clients; even if the base 
> operating system doesn't support time change, an NTP client can address 
> that.  So all my systems advanced appropriately, as did an old radio 
> clock.  I'm not sure how *nix does it, but I don't remember Ultrix 
> having the code on our 8650 (or 8700). Tops-20 will do the change 
> whether or not a client exists as the code is in the monitor.

NTP does actually not solve this at all. NTP does all time in UTC. It's 
up to the local machine to figure out if DST is applicable or not, and 
how to apply it.

> At the time (1980's), I don't believe that VMS had internal code to do 
> the time change and NTP did not exist as such (some network time 
> services existed, but I don't remember whether there was a generally 
> available VMS TCP/IP package; we didn't have it).  I would assume that 
> this is handled now.  I hesitate to ask about RSX and RSTS, but I would 
> assume that the C compiler for RSX (with Johnny's TCP/IP interface) 
> could support an NTP port.  Anyway, the question is: how does VMS handle 
> the time change?

As far as I know, VMS still use local time. The TCP/IP package have some 
handling of time zones and automatic DST. Exactly how it does it, 
though, I don't know. I suspect it might change the system time.

In RSX, it's all local time, for sure. I do have an NTP client already. 
I use a couple of logical names to tell what the offset from UTC is, and 
NTP makes use of that. And then I have a batch job which runs twice a 
year, at the time of the change between DST a not. And that batch job 
then changes the logical name values, as well as change the clock.

My NTP client, by the way, is in fact written in C. But it is my own 
implementation, and not something picked up from somewhere else.

   Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol