Replacing failed powersupplies on qbus PDP-11s

[Tony Duell]

> Simulation == all bets are off.  It's never going to tell you anything
> meaningful.

I wouldn't go that far, for all I am one of the people least likely to 
use or trust a simulation. I would say that a simulation is only as good 
as the model and the data, and that in most cases you haven't much of a clue 
about how either of those relates to reality. 

For example, a circuit similation may only be meanigful if you correctly 
handle the inductance of all the wires and the cpaactiance between them. 
Something that you might well not know accurately enough!.

If curse correctly, simulation can be useful. IMHO one of the frw correct 
ways (if not the only way) to use simulation is :

1) You have a real physical system that you do experiments on and collect 
real data

2) You simulate the same system under the same conditions and simulate 
the same experiements on that system

3) If the results agree, then it is likely (although not certain) that 
the simulation is an accurate description of the system and that tghe 
theory you used to produce the cimulation also applies to the real system

But if they results don't agree then either you have experimental 
measurement errors, a bug in the program, or more interestingly the 
theory doesn't apply to the real system, perhpas there is some other 
effect you've neglected. In which case you need to do more investigations.

-tony