[time-nuts] 60Hz mains clocking in computers

[Bill Hawkins]

Yes, the whole PDP-11 line used line frequency to update the real-time
clock.
DEC had a real-time operating system, very useful for emulation of analog
process control functions. Of course, an RTOS is more than just the clock.

We lost that anchor to real time in the interval between the PDP-11 and
NTP or SNTP when the microprocessors took over. All crystal clocks; time
of day (social time) set by anybody with a wristwatch.

Bill Hawkins
 

-----Original Message-----
From: paul swed
Sent: Saturday, December 12, 2009 10:09 PM

Talk about dusting off the old brain cells.
I seem to remember that the PDP 11/23s did indeed allow the use of the 60 hz
as an interrupt for precision timing if that can actually be said. The data
general nova 1200 also. Boy thats exposing ones age.

On Sat, Dec 12, 2009 at 8:29 PM, Colby Gutierrez-Kraybill <
colby at astro.berkeley.edu> wrote:

>
> I'm trying to get to the bottom of whether or not any computing equipment
> made around the advent of UNIX systems (or any time-slicing system) used
the
> mains cycles of 60Hz as phase lock for the internal system clock.  My
guess
> is that perhaps they did not as the computing logic is DC based, but, I
have
> memories of using an 68000 based UNIX system that I thought had its
internal
> clock based off of the 60Hz mains...  Not sure the vendor anymore.
>
> Thanks,  Colby
>