[FRIAM] naive question

[Steve Smith]

FWIW,  I dipped into the higher levels of real-time-systems development 
several times in my career.  The earliest being a control system (circa 
1981) for the LANL Proton Storage Ring where one naturally can't afford 
anything *but* failsafe implementations, etc. The stakes are just too 
'ffing high and the coupling to electrooptomechanical systems quite 
intimate.

The "digital" components of such systems might have had the opportunity 
to ignore timing issues and simply "execute the same steps" regardless 
of timing.  But in fact many software-driven (sub)systems represented 
time-critical processes and sometimes were up agains the timing limits 
of the analog components which had no leeway in their "execution".

There are all kinds of analogies in federated (distributed) simulation 
environments which Glen (and others here) probably know much better than 
I, where different "clocks" matter, and different levels of 
synchronization and reproducibility are in play.   The Postscript 
interpreters, printers, and film recorders were also pseudo real-time 
systems since some of the timing components were in fact software 
controlled (for example, the film recorders were "stroke" devices with 
software driving D-A converters to "sweep" out vectors and "clip" the 
on/off of the beam with appropriate analog component delays/biases/gains 
needing to be calibrated for.   Fortunately failures in this step did 
not (usually) damage anyone or risk anyone's health and safety (like the 
beam in the PSR did).

Regarding identity and equivalence, I prefer the phrase: "close enough 
for who it's for"...


On 10/21/22 11:18 AM, glen wrote:
> Ha! If we're going to argue about words, then let's stick with the 
> word "identity" and skip the "metaphor" nonsense. You and Frank seem 
> to be using the word in a weird way. Identity means "the exact same 
> particular thing over any differencing available" or somesuch. I mean, 
> it's used that way in phrases like "identity theft" as well as 
> mathematical identity. It's equivalence sets all the way down. I just 
> can't imagine any working computationalist would ever say anything 
> like "executed identically" unless ... well ... the exact same 
> process, with the exact same steps, happened.
>
> I suppose there are deep philosophical intuitions pried at by the 
> words "emulation" versus "simulation". And one can argue (again with 
> help from Christian List) about whether there exist fully closed 
> ontological walls like we try to create with things like Jails, 
> HyperV, Docker, VM's like Java's, etc. But "execute identically" is a 
> phrase that would only be used by someone who worked *way* above such 
> levels (assuming levels even exist at all). It's a bit like talking to 
> the kids programming websites these days, with access to infinite disk 
> space, infinite memory, steeped in continuous delivery, etc. [⛧]
>
> Layers of abstraction are fine. Use 'em when you need 'em. But we 
> shouldn't posture by invoking things like "instruction sets" and 
> "execute identically" in the same breath. (Not that you did that ... 
> just sayin'.)
>
>
> [⛧] Rant: This is a good talk 
> <https://www.youtube.com/watch?v=8Ab3ArE8W3s>. But I get super 
> irritated when people use *toy* code in their rhetoric and leave large 
> scale deployment as an exercise for the reader. Yeah, fine. The REPL 
> is cool and all. But when my simulation takes a fvcking WEEK to 
> execute, it's difficult to sympathize. I've recently been playing 
> around with VSCodium, which is pretty cool. But whatever, man. I still 
> have to upload the code somewhere and execute it. Get off my lawn!
>
> On 10/21/22 09:24, Steve Smith wrote:
>>
>> As a counter-example,  we ran film recorders whose "guts" were built 
>> by Ed Fredkin's Information International company and were built to 
>> the spec of Dec PDP-11 (I think 11?) and it was anecdotally agreed 
>> among the user community (of a few thousand delivered units in the 
>> world?) that these PDP-clones *never* failed to execute the code 
>> identically to the machines they were patterned after.   I don't 
>> remember the details of implementation of these 70's era hardware 
>> designs, but I understood that they III designed their own PCBs but 
>> (obviously?) used the same CPU chips... I don't know about all the 
>> other support components... A likely answer to this pondering is that 
>> these machines did not run a general purpose OS and the III 
>> software/system people probably made up for any differences in 
>> Software/Timing/Error Handling?
>>
>> If Owen is listening in here, I think he was there for more than a 
>> little of this from inside Apple/Sun?
>>
>> - Steve
>>
>> PS.   To concede/confront glen's sentiment that: " 'Metaphor' is an 
>> evil word, used only by manipulators and gaslighters",   I would 
>> offer that the use of *conceptual metaphor*  is to thinking as noise 
>> is to simulated annealing, and his point about "tighter or looser 
>> equivalence" might well be the best argument *for* the use of 
>> metaphorical thinking?  I can't believe I'm stirring/kicking this can 
>> of worm-hornets down the street again...
>>
>