[Info-vax] Databases versus RMS

[Paul Sture]

On Sat, 21 Apr 2012 13:34:12 +0200, Paul Sture wrote:

> On Fri, 20 Apr 2012 10:20:38 -0700, abrsvc wrote:
> 
>> In the days of the stepper motor, that was a problem.  In more modern
>> drives, the actuator arm is driven by a coil so no real friction or
>> contact points.  Usually it wouldbe in the "home" position as well  The
>> biggest problem was the current required to start the unit spinning.
>> With the drives spinning, the amount of power required to keep it that
>> way is significantly less than to start it spinning.  This allowed the
>> total power required to both spin and record the data to be much less
>> in both capacity and endurance.
> 
> There was a way to link up RM05 disks so that if you switched them all
> on at once they would only spin up one at a time.  The power draw of the
> four we had spinning up at the same time was enough to trip the circuit
> breaker.

A kind soul has sent me more details on those:

--- start quote ---

The power bus was common throughout all of the older and bigger boxes; a 
room full of RA or RF disks all spinning up together would blow breakers.


>From <http://users.bart.nl/users/pb0aia/vax/750faq.html#powerbus>

"What are the DEC Power Bus connectors for?

On the back of the power controller, there are two three-pin DEC Power 
Bus connectors, one labelled 'Normal' and the other labelled 'Delayed'. 
These are used to allow the front-panel keyswitch on the processor rack 
to control the mains supply to the other racks in the system. Pin 3 on 
each of the connectors is grounded. Pin 2 is an emergency shutdown: when 
grounded, it shuts the power system down. This is normally caused by a 
temperature sensor in either the processor rack or one of the other 
racks, or by the airflow sensor in the blower plenum signalling that the 
blower has failed. Pin 1 on each connector is a power-up request signal; 
when grounded by the front-panel keyswitch, it causes the power-
controller relay to close, supplying mains power to the PSU. On the 
'Delayed' connector, the power-up request output is delayed by about half 
a second; switching the other racks in your system from this output can 
prevent those embarrassing mains surges that trip the breaker on the 
mains ring and plunge the house into darkness...
Normally, the power controllers in all the racks of an installation are 
daisy-chained together, so that the front-panel keyswitch controls power 
to the whole system."

--- end quote ---


-- 
Paul Sture