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

Peter Coghlan cctalk at beyondthepale.ie
Mon Jan 19 06:23:30 CST 2015

>> 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.

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.

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

Peter Coghlan.

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