So in 50 years the equivalent of a gpt4 training cluster from today's datacenters will fit in a cheap cable, and it will run over 100 times faster than a full cluster today.
Yeap, that's how exponential growth works. It just never stops.
Apollo 11 vs. USB-C Chargers (2020)
161–170 of 209 posts
Re: Apollo 11 vs. USB-C Chargers (2020)
#162> the LVDC actually contains triply-redundant logic
I didn't know that was just for the LVDC.
> emulate this voting scheme with 3x microcontrollers with a 4th to tally votes will not make the system any more reliable
I think that's clear enough; the vote-tallier becomes a SPOF. I'm not sure how Tandem and Stratus handled discrepancies between their (twin) processors. Stratus used a pair of OTC 68K processors, which doesn't seem to mean voting; I can't see how you'd resolve a disagreement between just two voters.
I can't see how you make a voting-based "reliable" processor from OTC CPU chips; I imagine it would require each CPU to observe the outputs of the other two, and tell itself to stop voting if it loses a ballot. Which sounds to me like custom CPU hardware.
Any external hardware for comparing votes, telling a CPU to stop voting, and routing the vote-winning output, amounts to a vote-tallier, which is a SPOF. You could have three vote-talliers, checking up on one-another; but then you'd need a vote-tallier-tallier. It's turtles from then on down.
In general, having multiple CPUs voting as a way of improving reliability seems fraught, because it increases complexity, which reduces reliability.
Maybe making reliable processors amounts to just making processors that you can rely on.
Re: Apollo 11 vs. USB-C Chargers (2020)
#163I'm a bit tired of all the sensationalist "look what landed on the moon vs. today's hardware" comparisons. The first airplanes didn't have any sort of computer on board, so computation power is not the single deciding factor on the performance and success of such an endeavor. The software (and hardware) of the Apollo missions was very well-engineered. We all know computation became ridiculously more powerful in the m…
I don’t think you’re reading these articles in the right spirit if that’s your take away from them. What I find more interesting is to compare how complicated the tech we don’t think about has become. It’s amazing that a cable, not a smart device or even 80s digital watch, but a literal cable, has as much technology packed into it as Apollo 11 and we don’t even notice. Playing devils advocate for your comment, one of…
Your comment reminded me of this[0] video about the Jerry Can.
A simple looking object, but in reality it had a lot o tought put in to get to this form.
It also goes along the lines of "Simplicity is complicated"[1].
[0] - https://www.youtube.com/watch?v=XwUkbGHFAhs
[1] - https://go.dev/talks/2015/simplicity-is-complicated.slide#1
Re: Apollo 11 vs. USB-C Chargers (2020)
#164> The Anker PowerPort Atom PD 2 USB-C Wall Charger CPU is 563 times faster than the Apollo 11 Guidance Computer Wild to think the thing that charges my devices could be programmed to put a human on the moon
From that data point, we don’t know for sure. The Apollo Guidance Computer was programmed to put a human on the moon, but never used to actually do it, so no computer ever “put a human on the moon”. All landings used “fly by wire”, with an astronaut at the stick, and the thrusters controlled by software.
https://www.quora.com/Could-the-Apollo-Guidance-Computer-hav...:
“P64. At about 7,000 feet altitude (a point known as “high gate”), the computer switched automatically to P64. The computer was still doing all the flying, and steered the LM toward its landing target. However, the Commander could look at the landing site, and if he didn’t like it, could pick a different target and the computer would alter its course and steer toward that target.
At this point, they were to use one of three programs to complete the landing:
P66. This was the program that was actually used for all six lunar landings. A few hundred feet above the surface the Commander told the computer to switch to P66. This is what was commonly known as “manual mode”, although it wasn’t really. In this mode, the Commander steered the LM by telling the computer what he wanted to do, and the computer made it happen. This continued through landing.
P65. Here’s the automatic mode you asked about. If the computer remained in P64 until it was about 150 feet above the surface, then the computer automatically switched to P65, which took the LM all the way to the surface under computer control. The problem is that the computer had no way to look for obstacles or tell how level its target landing site was. On every flight, the Commander wanted to choose a different spot than where the computer was taking the LM, and so the Commander switched to P66 before the computer automatically switched to P65. [Update: The code for P65 was removed from the AGC on later flights. The programmers needed memory for additional code elsewhere, and the AGC was so memory-constrained that adding code one place meant removing something else. By that point it was obvious that none of the crews was ever going to use the automatic landing mode, so P65 was removed.]
P67. This is full-on honest-to-goodness manual mode. In P66, even though the pilot is steering, the computer is still in the loop. In P67, the computer is totally disengaged. It is still providing data, such as altitude and descent rate, but has no control over the vehicle.”
Re: Apollo 11 vs. USB-C Chargers (2020)
#165> the LVDC actually contains triply-redundant logic I didn't know that was just for the LVDC. > emulate this voting scheme with 3x microcontrollers with a 4th to tally votes will not make the system any more reliable I think that's clear enough; the vote-tallier becomes a SPOF. I'm not sure how Tandem and Stratus handled discrepancies between their (twin) processors. Stratus used a pair of OTC 68K processors, which d…
> I can't see how you'd resolve a disagreement between just two voters.
Tell them both to run the calculation again, perhaps?
Re: Apollo 11 vs. USB-C Chargers (2020)
#166Earlier quoted context omitted.
Analog computers have to be rebuilt if it turns out the program is wrong though, don’t they?
In the context of this thread, I believe even a digital computer would have to be rebuilt if the program is wrong... :P Unless you typically salvage digital computers from the wreckage of a failed rocket test and stick it in the next prototype. If the FCC is wrong, kaboom.
I had assumed it meant more simple things like balanced balancing pneumatic or mechanical components that always put you at the the correct ratio sort of like a carburetor vs fuel injection.
Re: Apollo 11 vs. USB-C Chargers (2020)
#167Earlier quoted context omitted.
This is a great technique to avoid common-mode failures.
Do you have data to back that claim up? I remember reading evidence to the contrary, namely that programmers working on the same problem -- even in different environments -- tend to produce roughly the same set of bugs. The conclusion of that study was that parallel development mainly accomplishes a false sense of security, and most of the additional reliability in those projects came from other sound engineering tec…
That was the reason for the different programming paradigms (Algol-like vs Prolog-like), to reduce the probability.
Re: Apollo 11 vs. USB-C Chargers (2020)
#168Earlier quoted context omitted.
Presumably they meant a program being discovered to be wrong before the computer was actually launched. And meant literally building a whole new computer, not just recompiling a program.
For the Apollo Guidance Computer, changing the program meant manually re-weaving wires through or around tiny magnet rings. A good part of the cost of the computer was the time spent painstakingly weaving the wires to store the program.
Pardon me, but why would you have to re-weave wires around magnetic rings? The magnetic rings are for storing data; the whole point is that you can change the data without rewiring the memory. If you have to re-wire permanent storage (e.g. program storage), that's equivalent to creating a mask ROM, which is basically just two funny-shaped sheets of conductor. There's no need for magnetic rings.
Re: Apollo 11 vs. USB-C Chargers (2020)
#169Earlier quoted context omitted.
That sounds way too low. Modern fly-by-wire planes are said to have 12-way voting.
It's more complicated than that, in the link, they described it better: >> The microcontrollers, running on PowerPC processors, received three commands from the three flight strings. They act as a judge to choose the correct course of actions. If all three strings are in agreement the microcontroller executes the command, but if 1 of the 3 is bad, it will go with the strings that have previously been correct. This is…
> Byzantine Tolerant Concensus
I was taken to task for mis-spelling "consensus"; I used to spell it with two 'c's and two 's's, like you. It was explained to me that it's from the same root as "consent", and that's how I remember the right spelling now.
Re: Apollo 11 vs. USB-C Chargers (2020)
#170Earlier quoted context omitted.
> is the game? Sure. One of the "Surprisingly Turing-Complete" examples is that "Magic: the Gathering: not just TC, but above arithmetic in the hierarchy ". See https://arxiv.org/abs/1904.09828 for the preprint "Magic: The Gathering is Turing Complete", https://arstechnica.com/science/2019/06/its-possible-to-buil... for an Ars Technica article, and https://hn.algolia.com/?q=magic+turing for the many HN submissions on…
Could you explain "above arithmetic in the hierarchy" in a few words, TIA, never heard of this
Nope. The source page links to https://en.wikipedia.org/wiki/Arithmetical_hierarchy . I can't figure it out.
An HN comment search, https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu... , finds a few more lay examples, with https://news.ycombinator.com/item?id=21210043 by dwohnitmok being the easiest for me to somewhat make sense of.
I think the idea is, suppose you have an oracle which tells you if a Turning machine will halt, in finite time. There will still halting problems for that oracle system, which requires an oracle from a higher level system. (That is how I interpret "an oracle that magically gives you the answer to the halting problem for a lower number of interleavings will have its own halting problem it cannot decide in higher numbers of interleavings").