[time-nuts] 60Hz mains clocking in computers

Uno Staver uno at staver.se
Tue Apr 20 08:28:14 EDT 2010


Since many of us are not so old as I am, and aren't familiar with the 
PDP-11 family, I should have mentioned that this happened in the middle 
80's.

Uno Staver wrote:
> We bought a bunch of PDP-11/23s as part of a communications network 
> system. After successful acceptance tests in Boston, MA, the systems 
> were commissioned in Sweden with 50Hz AC. To make the RSX-11M O/S 
> time-of-day clock run OK, the developers modified some piece of code.
> 
> 
> Uno Staver
> 
> 
> Bill Hawkins wrote:
>> 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
>>>
>>
>>
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> 
> 
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