Does anyone on HN can explain this question to me: is there a real obstacle that prevents one to build a general-purpose digital computer using pure macroscopic mechanical components? Historically, we had several types of special-purpose mechanical computers, but a general-purpose mechanical computer was never built.
Was it because the mechanical parts are too prohibitively rigid/inflexible/heavy/expensive for a computer? Or, a real barrier for mechanical computers doesn't really exist, and we didn't have it simply because it was not economically worthwhile to build one after electronic computers were feasible?
First computers used relays, becase they were already faster and cheaper than purely mechanical computer. Then came lamps which were even faster. Nowadays mechanical computers are just uneconomical curiosity, but thanks to miniturisation they look like they might be economical for several VERY special purposes where silicon just doesn't work.
> Was it because the mechanical parts are too prohibitively rigid/inflexible/heavy/expensive for a computer?
Yes, and it was all those reasons at once. Electrical/electronical computers were better at every metric simultaneously.
You might want to read up on https://en.wikipedia.org/wiki/Analytical_Engine There is good reason to believe that it can actually be built, and a simpler design that is not general-purpose is exhibited in the Science Museum in London.
Thanks, I confused Differential Engine and Analytical Engine, and believed the latter was a more much powerful version, but still not general-purpose. But apparently Analytical Engine is Turing-complete.
Not an expert, but two obvious issues come to mind:
1) Energy loss due to friction & constantly working against inertia (regular and rotational).
2) I don't think you could get anywhere close to even a kilohertz without the whole contraption shaking itself apart. When we say a CPU has a clock of 1GHz, this literally means some components are being activated and deactivated a billion times a second.
Both problems seem to be correlated with size. That is, the smaller it gets, the faster a mechanism can run.
Not sure if possible, but I've found the idea of building a general-purpose fluidics machine fascinating. This might solve the problem in (1).
I do agree with (2) though - I think anything macroscale would simple be orders of magnitude slower than what we can archieve at microscale. I don't know if there is any way out of this.
> I think anything macroscale would simple be orders of magnitude slower than what we can archieve at microscale. I don't know if there is any way out of this.
This is what I was wondering about.
A general-purpose computer, abierto how slow, is still a computer that can process huge amount of computation. Back in the 19th century, the availability of many mathematical and engineering tables was still a problem. And in 1920s, to calculate the requirements of the Afsluitdijk dam project in the Netherlands, the famed physicist Lorentz helped deriving a model from basic fluid dynamics, and it took several years to run the "computer simulation" - to calculate the differential equations in that model numerically by a team of human computers.
Lorentz said,
> The numerical calculations were so lengthy, that we came close to the ultimate limit of what can be done in this way. I myself had no part in this. I did try once or twice to set up and work out such a calculation, but then it would turn out that I had made a mistake, so that it had to be done all over again by others.
As it has been pointed out, Analytical Engine was a real possibility and unlike the Differential Engine, it was genuinely Turing-complete (I thought it was just a numerical solver, and believed Bruce Sterling's Sci-Fi was a bit exaggeration). Just imagine how the course of history would change if some military or industrial funding in the 18th century went to build such a computer instead...
You should have a look at the old IBM Hollerith machines. Although I think they count as electro-mechanical.
> a real barrier for mechanical computers doesn't really exist, and we didn't have it simply because it was not economically worthwhile to build one after electronic computers were feasible
Bit of both: electronics is easier to miniturise, and as a result of that it's easier to manufacture, easier to maintain, lighter, and consumes less power.
Speed of operation of a mechanical computer is limited by the acceleration of the parts.
Was it because the mechanical parts are too prohibitively rigid/inflexible/heavy/expensive for a computer? Or, a real barrier for mechanical computers doesn't really exist, and we didn't have it simply because it was not economically worthwhile to build one after electronic computers were feasible?