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Apollo 11 vs. USB-C Chargers (2020)

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Re: Apollo 11 vs. USB-C Chargers (2020)

#151

Post by demondemidi »

kristopolous wrote: post #14
GlenTheMachine wrote: post #8

Earlier quoted context omitted.

They won’t be. We will use RAD750’s, the flight qualified variant of the PowerPC architecture. That’s the standard high end flight processor. https://www.petervis.com/Vintage%20Chips/PowerPC%20750/RAD75... The next generation (at least according to NASA) will be RISC-V variants: https://www.zdnet.com/article/nasa-has-chosen-these-cpus-to-...

The 750 is still based on a 27 year old chip and runs at half its clockspeed. The point was that spaceflight is relatively computationally modest.

Reliability is more important. Even more problematic is that many semi companies have been funneled into just a few due decades of mergers. And all of these are chasing profits which means jettisoning RAD hard mil spec devices. Up until the early 2000s intel was still making hardened versions of the 386, now they make no milspec parts.

Re: Apollo 11 vs. USB-C Chargers (2020)

#152

Post by Dah00n »

kqr wrote: post #140
ThePowerOfFuet wrote: post #134

Earlier 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…

Isn't this exactly what aeroplanes do? Two or more control systems made in different hardware, etc?

Re: Apollo 11 vs. USB-C Chargers (2020)

#153

Post by Dah00n »

lmm wrote: post #73
hinkley wrote: post #66

Earlier quoted context omitted.

Have you ever tried to google that?

Yes - up until a few years ago it was easy to find by googling, but now google has degraded to the point where I can't manage it.

Yeah sure, people on HN says this all the time, but in reality it isn't true like a lot of comments getting repeated on here. I found it on the first try.

Re: Apollo 11 vs. USB-C Chargers (2020)

#154

Post by deaddodo »

milkey_mouse wrote: post #135
kragen wrote: post #92

Earlier quoted context omitted.

i think it's (unintentionally) misleading to describe analog 'computers' as 'computers'. what distinguishes digital computers from other digital hardware is that they're turing-complete (if given access to enough memory), and there isn't any similar notion in the analog domain the only reason they have the same name is that they were both originally built to replace people cranking out calculations on mechanical desk…

https://www.gleech.org/first-computers

If you just want to reference the entire data set of potential "first computers" (including ones that aren't referable in the javaScript app, due to missing toggles), you can access the source data here (warning, small CSV download):

https://www.gleech.org/files/computers.csv

Re: Apollo 11 vs. USB-C Chargers (2020)

#155

Post by bregma »

codezero wrote: post #35

Weird question maybe, but does anyone keep track of quantitative or qualitative data that measures the discrepancy between consumer (commercial) and government computer technology? TBH, it's kind of amazing that a custom computer from 50 years ago has the specs of a common IC/SoC today, but those specs scale with time.

By 'government' do you mean banks and large industrial concerns (like the "industry" in "military-industrial complex")? The latter are where all the big iron and massive compute power has always been.

If course, from a certain point of view, they're many of the same people and money.

Re: Apollo 11 vs. USB-C Chargers (2020)

#156

Post by eru »

kragen wrote: post #92
kens wrote: post #16

> Apollo 11 spacecraft contains 4 computers Analog computers don't get the respect they deserve. There's one more computer, the FCC. The Flight Control Computer is an analog computer in the Saturn V that controlled the rocket gimbals. It's a two-foot cylinder weighing almost 100 pounds.

i think it's (unintentionally) misleading to describe analog 'computers' as 'computers'. what distinguishes digital computers from other digital hardware is that they're turing-complete (if given access to enough memory), and there isn't any similar notion in the analog domain the only reason they have the same name is that they were both originally built to replace people cranking out calculations on mechanical desk…

Most digital computers are Turing complete, but interestingly not all programming languages are Turing complete.

Turing completeness is a tar pit that makes your code hard to analyse and optimise. It's an interesting challenge to find languages that allow meaningful and useful computation that are not Turing complete. Regular expressions and SQL-style relational algebra (but not Perl-style regular expressions nor most real-world SQL dialects) are examples familiar to many programmers.

Programming languages like Agda and Idris that require that you prove that your programs terminate [0] are another interesting example, less familiar to people.

[0] It's slightly more sophisticated than this: you can also write event-loops that go on forever, but you have to prove that your program does some new IO after a finite amount of time. (Everything oversimplified here.)

Re: Apollo 11 vs. USB-C Chargers (2020)

#157

Post by kqr »

Dah00n wrote: post #152
kqr wrote: post #140

Earlier quoted context omitted.

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…

Isn't this exactly what aeroplanes do? Two or more control systems made in different hardware, etc?

I'm not saying people aren't doing it! I'm just not sure it has the intended effect.

(Also to protect against physical failures it works, because physical failures are more independent than software ones, as far as I understand.)

Re: Apollo 11 vs. USB-C Chargers (2020)

#158

Post by nine_k »

kragen wrote: post #92
kens wrote: post #16

> Apollo 11 spacecraft contains 4 computers Analog computers don't get the respect they deserve. There's one more computer, the FCC. The Flight Control Computer is an analog computer in the Saturn V that controlled the rocket gimbals. It's a two-foot cylinder weighing almost 100 pounds.

i think it's (unintentionally) misleading to describe analog 'computers' as 'computers'. what distinguishes digital computers from other digital hardware is that they're turing-complete (if given access to enough memory), and there isn't any similar notion in the analog domain the only reason they have the same name is that they were both originally built to replace people cranking out calculations on mechanical desk…

In analog computers, software is hard to separate from the hardware. In ones I had any experience with (as a part of a university course), the programming part was wiring things on patch panels, not unlike how you do it with modular analog synths. You could make the same machine run a really wide variety of analog calculations by connecting opamps and passive components in various ways.

If we could optimize a set of programs down to the FPGA bitstream or even Verilog level, that would approach the kind of programs analog computers run.

I can't tell anything about Turing completeness though. It's a fully discrete concept, and analog computers operate in the continuous signal domain.

Re: Apollo 11 vs. USB-C Chargers (2020)

#159

Post by argiopetech »

hnlmorg wrote: post #148
blauditore wrote: post #136

I'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…

This is actually about the wall warts the cable could be plugged into.

Otherwise, I completely agree.

Re: Apollo 11 vs. USB-C Chargers (2020)

#160

Post by couchand »

fanf2 wrote: post #146
kragen wrote: post #121

Earlier quoted context omitted.

as i understand it, with infinite precision; the real numbers within some range, say -15 volts to +15 volts, have a bijection to infinite strings of bits (some infinitesimally small fraction of which are all zeroes after a finite count). with things like the logistic map you can amplify arbitrarily small differences into totally different system trajectories; usually when we plot bifurcation diagrams from the logisti…

Except that infinite precision requires infinite settling time. (Which I guess is the analogue computing version of arithmetic not being O(1) even though it is usually modelled that way.)

Infinite precision is just analog's version of an infinitely-long tape.
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