Operating systems of the 1970s handling dates beyond the year 2000

Johnny Billquist bqt at update.uu.se
Mon Jan 19 07:15:38 CST 2015

On 2015-01-19 13:23, Peter Coghlan wrote:
>>> After trying to get Unix v5 to understand dates beyond the year 2000 I
>>> had to wonder if any of the older operating systems from the 1970s or
>>> older could do this.
>>> So, did any operating system programmers from this time period have
>>> the foresight to use 4 digits for the year? I just checked APL/360 and
>>> it seems that it does not.
>> TOPS-20? VMS?
> It was very near the end of the 1970s but VMS made a really good effort to
> handle times and dates well from the beginning.  A single 64 bit time format
> is used throughout the operating system and operating system routines are
> provided to manipulate it and convert to and from well chosen standardised
> display formats with no ambiguities such as two digit years or easily mixed up
> numbers for days and months.  Everything [*] displays and accepts the same
> time and date formats and shortcuts such as YESTERDAY, TODAY and TOMORROW.
> No messing about trying to figure out what format a particular utility wants
> the date specified in and no wondering whether a unitless time displayed by
> something is days, hours or minutes.

Agreed. But VMS was released in 1977. Possibly realy 1978, so it wasn't 
"very near the end of the 70s" I think.

> The areas where I think it could have been done better still are to have stored
> the time internally in UTC rather than local time while displaying local time
> and to have chosen an earlier base date than 17 November 1858.  Also, there was
> originally a rule that time differences could not be larger than 10000 days
> which was poorly enforced and eventually had to be scrapped - this should have
> been handled much more gracefully.

The local time problem is a serious miss that VMS did.

The 10000 day limit was a problem that hit the C runtime library, since 
C programs like to, and expect code, to express time as an offset from 
the epoch, which is Jan 1, 1970.
Of course, VMS used delta times for this, and that hit 10000 days a 
little while ago, which barfed things up. I don't remember offhand 
exactly what the solution looked like.
Nothing else normally ever had any issues with that limit, but I think 
it was rather arbitrary, so I don't expect any programs had problems 
with raising the limit either.

> [*] A few system parameters are specified in seconds and TIMEPROMPTWAIT is
> specified in microfortnights with tongue in cheek.



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

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