Gears of war: When mechanical analog computers ruled the waves

http://arstechnica.com/information-technology/2014/03/gears-of-war-when-mechanical-analog-computers-ruled-the-waves/

by haomiao • 12 years ago

53 16 12 years ago

Cogito• 12 years ago

An interesting article, but it annoys me when the author talks of analog computers having "an infinite level of resolution... because they use physical rather than digital inputs and outputs".

Physical machines have varying levels of tolerance, and this impacts the accuracy of calculations in just the same way as a truncated number in a digital system reduces accuracy.

It was a lot more interesting to read about the pros and cons of digital vs analog computers with respect to maintenance, reprogrammability, energy use, and reliability. It's a pity there wasn't a similarly in-depth account of the precision of each system.

jjoonathan4• 12 years ago

Yep, it's embarrassing that this got published. Did the author just forget about mechanical tolerance? The random motion of molecules? Ambient sound waves? Electromagnetic noise?

I suppose it's forgivable that the author didn't think of these things but they should have run their technical article past a subject expert before publishing it. This isn't a nitpick, they screwed up the core concept of their article!

there wasn't a similarly in-depth account of the precision of each system

That's because digital circuits won the "precision wars" so spectacularly that there was no need for comparison. On a digital computer, you can just keep adding bits to your datatype, doubling your precision with each bit, until you are happy. Bits cost almost nothing today (and very little 30 years ago) so you use as many as you need. If you underestimate how many you need, that's a planning problem, not a limitation of the digital technique. Meanwhile, the price of increasing the precision of an analog computer (mechanical, electrical, or fluidic) shoots up dramatically after a few decimal places and goes to infinity after a few more. That is a limitation of the analog technique.

Here's a fun demo of how the digital nature of a circuit grants it complete noise immunity (within tolerances), unlike any analog circuit that could ever be built:

https://www.youtube.com/watch?v=4TCnYYpZxEc#t=2806

eru3• 12 years ago

Without improving tolerances, the only way out is to go bigger.

agoetz• 12 years ago

Make a circuit "digital" does not automagically make it more accurate, and you cannot "add bits" to a datatype to make your measurement more accurate.

Before a digital circuit can process a signal, it must first be quantized, an inherently analog process. Your digital data is only as good as your analog signal, plus inherent quantization noise[1]. In addition, any mixed-signal IC represents a design compromise between digital and analog constraints.

Any signal processing system is inherently limited by the SNR of its source signal. There is no point in building a more accurate converter than the noisiest component of your input data. In fact, when metrologists are trying achieve the maximum accuracy in their measurements, it is not uncommon to leave a test circuit on for days at a time, in order to reach a thermal equilibrium to minimize the seebeck effect[2].

And when engineers to need to make the most accurate of measurements, what do they turn to? Analog circuits. The world's most accurate voltage reference, the Kelvin-Varley Divider, dates back to the late 19th century[3]. For a modern example of a precision reference, see Jim William's excellent white paper, "Quantifying Silence"[4].

[1] http://en.wikipedia.org/wiki/Quantization_(signal_processing...

[2] http://www.keithley.com/knowledgecenter/knowledgecenter_pdf/...

[3] http://en.wikipedia.org/wiki/Kelvin%E2%80%93Varley_divider

[4] http://cds.linear.com/docs/en/application-note/an124f.pdf

mikelbring• 12 years ago

No not about the video game.

NamTaf• 12 years ago

Obligatory link to youtube video of a 1950s training video on the mechanical fire control computers (which I stole from HN last time this sort of topic came up):

https://www.youtube.com/watch?v=s1i-dnAH9Y4

edit: This video is the same footage featured throughout the article, in fact.

D9u2• 12 years ago

Ah... You beat me to it!

D9u2• 12 years ago

Interestingly, several months ago I came across the following 1953 training video dealing with this same subject.

http://youtu.be/s1i-dnAH9Y4

nnq• 12 years ago

off topic, but did anyone pay attention the Juniper deception force adds they sport?

This line of one commercial just blew my mind: 'the less they know, the safer they are' ...can a security oriented company actually get away with saying that?!

spingsprong• 12 years ago

Some of these analogue computers are pretty amazing things.

I can kinda get my head around slow moving ships being tracked by a mechanical computer, but the Russian ZSU-23-4 Shilka self propelled anti-aircraft artillery vehicle used an electro mechanical gun aiming computer in the 60s and 70s.

A mechanical computer that can track a supersonic rapidly manoeuvring jet aircraft by radar, and adjust the aim of its guns quickly enough and accurately enough to score hits. It's amazing what can be achieved.

Gears of war: When mechanical analog computers ruled the waves

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