Analog Computers: Digital vs. Theoretical Possibilities

[ISamson]

There are two types of 'reading'. Digital and analog. There are digital computers, which function with 'on' and 'off' data. But can it possible to construct an analog computer? Can it be theoretically possible?

 

[fresh_42]

There are two types of 'reading'. Digital and analog. There are digital computers, which function with 'on' and 'off' data. But can it possible to construct an analog computer? Can it be theoretically possible?

Not only theoretically: https://en.wikipedia.org/wiki/Analog_computer
In the end it depends on what you allow to be called a computer. There are even more examples on other Wikipedia language pages, so I suppose those examples can also be found in English on some webpages.

 

[Vanadium 50]

https://en.wikipedia.org/wiki/Analog_computer

You've been here long enough that you should know you have to put in some effort.

 

[lekh2003]

Do you think this is relevant: https://en.wikipedia.org/wiki/Antikythera_mechanism

It is probably the world's first scientific calculator discovered in a shipwreck in 1901. Apparently it was built by the Ancient Greeks. Analog computers have been around a long time.

 

[ISamson]

Do you think this is relevant: https://en.wikipedia.org/wiki/Antikythera_mechanism

Greeks had computers. Cool!
Well, a mechanism to be precise...

 

[lekh2003]

Greeks had computers. Cool!
Well, a mechanism to be precise...

But still a computer, again, anything can be a computer. I like to think of a computer as a man-made machine with automated computational abilities. So this would include something like the Antikythera machine, but would exclude an abacus.

 

[ISamson]

Why are analog computres utilised nowadays, how are they useful or more convenient in some ways than digital, normal, computers?
If such analog computers are used, then how are they better than digital?
I don't understand this.

 

[lekh2003]

Why are analog computres utilised nowadays, how are they useful or more convenient in some ways than digital, normal, computers?
If such analog computers are used, then how are they better than digital?
I don't understand this.

Well, for starters they won't require electricity. I don't think the Ancient Greeks had anything like electricity so how in the world would they make a digital computer. In today's world, I can't think of any advantage besides not needing electricity. Analog computers are simply too big and bulky and do too little. Simple multiplication machines are the sizes of rooms (you could make it smaller and more efficient, but why?).

 

[ISamson]

But still a computer, again, anything can be a computer. I like to think of a computer as a man-made machine with automated computational abilities.

A computer is a device that can be instructed to carry out arbitrary sequences of arithmetic or logical operations automatically. The ability of computers to follow generalized sets of operations, called programs, enables them to perform an extremely wide range of tasks.

https://en.wikipedia.org/wiki/Computer

I think it is more accurate to think of it as a device capable of operating logic in computationally and mathenatically logical ways.

 

[lekh2003]

I think it is more accurate to think of it as a device capable of operating logic in computationally and mathenatically logical ways.

Well that's the definition of automated computational abilities.

 

[ISamson]

I can't think of any advantage besides not needing electricity.

How does a computer not need electricity? How on earth?

 

[lekh2003]

How does a computer not need electricity? How on earth?

It's an analog computer, it can use mechanical energy and convert that into motion to run its parts. There are a plethora of methods. Take a look here: https://en.wikipedia.org/wiki/Analog_computer#Mechanical_analog_computers

You can find this stuff online, my friend.

 

[fresh_42]

A slide rule is certainly a computer, because you can do computations with it. And it is without electricity as well as analog.

 

[ISamson]

In recent years, analog computers have proven to be much more efficient at simulating biological systems than digital computers. But existing analog computers have to be programmed by hand, a complex process that would be prohibitively time consuming for large-scale simulations.

The work could help pave the way to highly efficient, highly accurate analog simulations of entire organs, if not organisms.

http://news.mit.edu/2016/analog-computing-organs-organisms-0620

 

[lekh2003]

http://news.mit.edu/2016/analog-computing-organs-organisms-0620

Yeah, but then again, they just said how difficult it is. You have to mechanically fix everything, not as easy as coding. To create a fully functioning organism, the analog computer would take decades to build and would occupy a city.

 

[ISamson]

You can find this stuff online, my friend.

If you are talking about mechanical, not electrical, or silicon computing, then you are totally right!

 

[Rive]

Why are analog computres utilised nowadays, how are they useful or more convenient in some ways than digital, normal, computers?
If such analog computers are used, then how are they better than digital?
I don't understand this.

Nowadays this art can be considered as a dead end. There are still some examples when analog functions are implemented with the knowledge and parts originated from analog computers, but that's all. Microcontrollers and AD-DA converters are so cheap, that most cases it's just faster, cheaper and more flexible to do everything digital.

In theory, analog computers were way more sturdy in some environments, and such things like a random high energy particle was just a source of some additional error instead of a deathblow (like it is for a common digital circuit).

 

[Borek]

Analog computer can be easily an electrical one. Nothing unusual to use an electrical circuit to simulate a process and read the results from a voltmeter.

My Mom in front of an analog electrical grid simulator, early sixties:

 

[Svein]

Analog computers...

Of course you can add and subtract voltages with op-amps. You can also take logs and do exponentials. There are multiplying circuits (http://www.analog.com/media/en/training-seminars/tutorials/MT-079.pdf) as well.

So what else do you want to do?

 

[ISamson]

Analog computer can be easily an electrical one. Nothing unusual to use an electrical circuit to simulate a process and read the results from a voltmeter.

Voltimeter? That easy?
Do you have a link?

 

[ISamson]

Of course you can add and subtract voltages with op-amps. You can also take logs and do exponentials. There are multiplying circuits (http://www.analog.com/media/en/training-seminars/tutorials/MT-079.pdf) as well.

Thank you. Extremely good link!
But a bit complex...

 

[Rive]

Voltimeter? That easy?

It's just unusual but not really different than what you get from a common calculator...

 

[Borek]

It's just unusual but not really different than what you get from a common calculator...

Completely different. Do you understand the difference between analog and digital?

 

[Rive]

Completely different. Do you understand the difference between analog and digital?

Yes. In this case: around 1% accuracy vs. 8 digit accuracy.

(C'mon, both are simple, one dimensional readings...)

 

[phinds]

Greeks had computers. Cool!
Well, a mechanism to be precise...

Keep in mind that the word "computer" was first applied to PEOPLE, not machines.

 

[donpacino]

Even in the modern day the "flight control computers" on some aircraft are all analog (granted the products in design now are not).

 

[donpacino]

http://www.popularmechanics.com/mil...r-were-a-mid-century-engineering-masterpiece/
So the B-29 had one of the first advanced electronic computing systems that were not the size of a room during ww2. Read the above article!

TLDR: The B-29 was pressurized so to utilize less crew and allow the crew to properly aim weapons, the machine gun turrets were controlled via an analog computer and remote control. They even had logic to prevent the aircraft hitting itself.

 

[donpacino]

Yes. In this case: around 1% accuracy vs. 8 digit accuracy.

(C'mon, both are simple, one dimensional readings...)

There is no such thing as a purely digital voltmeter. A digital voltmeter is an analog voltmeter with a digital interface to the outside world along with possibly (depending on the model) some process and function handling in the digital domain as well.

His question was not regarding accuracy. It was do you understand the differences beneath the hood.

 

[CWatters]

Here is a water based analogue computer from 1949 running a simulation of the UK economy...

 

[Rive]

There is no such thing as a purely digital voltmeter.

Since the topic is about (analog) computing, the analog/digital measurement is completely off. What matters is, the type of output, what's a single number in this case: the same what a common (digital) calculator would provide. To mix in the type of output is kind of like setting up categories on computer performance according to display type (CRT, LCD).
That was behind my slightly sarcastic answer about accuracy.

 

[donpacino]

That was behind my slightly sarcastic answer about accuracy.

It was a VERY relevant question posed to you that you did not fully answer and partially answered with sarcasm.

Since the topic is about (analog) computing, the analog/digital measurement is completely off. What matters is, the type of output, what's a single number in this case: the same what a common calculator would provide. To mix in the type of output is kind of like setting up categories on computer performance according to display type (CRT, LCD).

That is not true at all. How things work under the hood can very much effect the outcome, regardless of the data presentation, which leads me to follow up with Borek's question, do you know the difference between analog and digital. It's not just about display type.

 

[Rive]

It was a VERY relevant question posed to you that you did not fully answer and partially answered with sarcasm.

If you are so into hair splitting then please notice that in that answer I already used percents and digits.

To clarify - the answer for that question is 'YES'.

 

[donpacino]

If you are so into hair splitting then please notice that in that answer I already used percents and digits.

To clarify - the answer for that irrelevant question is 'YES'.

Digital systems can report in % accuracy too, referring to the difference between analog and digital domains as percents vs digits implies you don't understand the difference. You also referred to a voltmeter comment with "It's just unusual but not really different than what you get from a common calculator..." which implies you don't have a good level of understanding, as there are older calculators that compute using analog methods. Responding to people trying to help you by being sarcastic and rude is not good form.

 

[ISamson]

Completely different. Do you understand the difference between analog and digital?

I do. I think I do.
Digital can be either two states, High or Low in measurment, or 1 or 0 in computing. Analog can be any state or value possible.
I like to think of it as time measurment: digital and analog clocks. Digital can either be 21:02:45 or 21:02:46. Nothing in between. Analog can be basically anything in between the two seconds, minutes or hours. Is that accurate?

Keep in mind that the word "computer" was first applied to PEOPLE, not machines.

How?
Thank you for all the replys.

 

[phinds]

How?

You should learn to use Google.

Word Origin and History for computer n. 1640s, "one who calculates,"

 

[Svein]

Analog, digital and voltmeters...

Let's see. A 12 bit ADC (analog-to-digital converter) is relatively inexpensive. So the output (12 bit) should be within 1 bit. 1 bit in 12bit equals 1/4096 or 0.024%.

How do you produce an analog front-end with 0.024% accuracy?

And - worse - how do you keep that accuracy over the wanted temperature range?

Sadly, people tend to trust every digital bit even if the low-order bits are pure nonsense.

Once upon a time - some customers wanted us to measure the pressure in the fuel lines of a jet engine. In order to have a precise measurement, they wanted a 16 bit ADC. 1 bit in 16bit equals 1/65536 or about 16ppm. Even if we could measure pressure that accurate, what with the noise and vibration from the jet engine at >100dB? The customer is always right, so they got their 16bit ADCs - and a hefty digital filter backend to remove the noise.

 

[jim hardy]

@ is not working again

@ISamson
As recently as the 1960's digital computers were just too slow to solve differential equations quickly.
I worked in a factory that made computers for Cape Canaveral, they were hybrids.
A digital computer set the adjustable resistors in an analog computer that solved the equations and read the answers at desired times.
The adjustable resistors were plain old multiturn potentiometers turned by tiny motors under control of the digital computer.

If there are any left today they're relics.
https://archive.org/stream/TNM_Milg...ter_System_-_Milgo_Ele_20171110_0135_djvu.txt

oh my goodness here's a picture of the assembly line !
https://www.floridamemory.com/items/show/38724
this should take care of the copyright

Milgo Electronic Corp. technicians working on computer production line - Miami, Florida. 196-?. Black & white photoprint, 8 x 10 in. State Archives of Florida, Florida Memory. <https://www.floridamemory.com/items/show/38724>, accessed 11 January 2018.

 

[Phillip81]

I like this. I have always wondered 1 important aspect of computing, what is analog?
Everyone assumes an analog computer is mechanical in nature. What if it was PWM instead. so use 0-1023 instead of 0 and 1. my poor little brain has no idea about transistor and the like but with about 100 arduino nano's taking a read and writing to the next you could make a baby analog for just on $200 (if you buy the el cheapo).
theoretically I believe that you could make a program that needs less junctions to get the end result. so 1 +1 in binary is 8 bits + 8 bits. in analog it could be 1 digit plus 1 digit. The only Issue I foresee in my way of doing it is that you go analog to ditital to analog to digital... over and over and over again.

 

[Rive]

I have always wondered 1 important aspect of computing, what is analog? ... What if it was PWM instead. so use 0-1023 instead of 0 and 1..

Binary logic is just the most common and practical variation of 'digital', it is not absolute. In theory, there is no issue with - for example - ten state logic.
This way what makes the difference between analog and digital is not the amount or value of signal levels, but the way of computing. If you (your equipment) does the computing digit by digit logic, with keeping the logic levels discrete then it's still digital.

theoretically I believe that you could make a program that needs less junctions to get the end result.

In theory, you are right... But the practical part is totally different. To make a not-binary digital system is quite a challenge.

Ps.: well, I mean it's a challenge if you want to make it in electronics. The classic pen-and-paper calculation method is a good example for non-binary digital 'system'.

Ps2.: since at young age it takes some years to master it, maybe we can still recognize it as a challenge

 

[Asymptotic]

As recently as the 1960's digital computers were just too slow to solve differential equations quickly.
I worked in a factory that made computers for Cape Canaveral, they were hybrids.

What was old is new again :)
"Not Your Father's Analog Computer". From the article,

The analog processing on a computer of the type my colleagues and I have developed typically takes about a millisecond. The solution of differential equations that involve only one derivative typically requires less than 0.1 microjoules of energy on our computer. And it takes one half of a square millimeter of chip area if we use plain-vanilla fabrication technology (65-nm CMOS). Equations that involve two derivatives take twice as much energy and area, and so forth; yet the solution time remains the same.
...
With a 300-millimeter wafer, this would permit more than 100,000 integrators to be placed on the chip, thus allowing it to simulate a system of 100,000 coupled first-order nonlinear dynamical equations, or 50,000 second-order ones, and so forth. This might be useful, for example, in simulating the dynamics of a large array of molecules. The solution time would still be in the milliseconds, and the power dissipation in the tens of watts.

 

[FactChecker]

The F-16, F-111, and several other fighters had analog computers for their flight controls till the mid 80's. It was easier to design their response to the dynamic frequencies of the airplane. As long as the logic switching remained relatively simple (compared to modern flight controls), analog computers worked well. There is a trade-off between analog and digital computers. Analog computers have no trouble responding to very fast frequencies but have trouble with complicated logic. Digital computers can handle incredibly complicated logic, but may not do it fast enough for high frequency responses. Modern fighter flight controls can be incredibly complicated and push the fastest digital processors to their limits.

 

[Babadag]

In my opinion, the word “analogue”, like many words in English - meant something else initially. Now any device that is not digital is considered analog-even mechanical one. The analogue word was used for circuits that could mimic arithmetical operations as sum, difference, division, and even integral. See https://en.wikipedia.org/wiki/Operational_amplifier
So it was once upon a time an analog computer. However, there were mechanical computers also [see for instance “Enigma” German product in WWII].
https://en.wikipedia.org/wiki/Enigma_machine

 

[Baluncore]

A GPU with over a thousand processors, each running at better than 1 GHz, is capable of emulating a few hundred analogue computers in real time. If you don't believe it, design your analogue computer, model it with SPICE, and run it on a PC.

I have yet to find a true digital gate used in a digital computer. Every logic gate is a circuit made from transistors, resistors, diodes and wires. The circuits implement an analogue of the boolean logic functions.

Consider two voltages, A and B, each varying between 0 and 1 volt, each representing the probability of that particular input being true. An AND gate can then be a simple multiplier. The output voltage, Z, will be the probability of both inputs being true. Z=A*B. If both inputs had a probability of 0.5V then the output would be 0.25V which makes statistical sense. An inverter would be made from a subtractor, Z=1–A. Then the NAND gate becomes Z=1– A*B. The set of basic functions becomes;
NOT(A) = 1–A
AND(A,B) = A*B
NAND(A,B) = 1– A*B
NOR(A,B) = (1–A)*(1–B)
OR(A,B) = 1 – ( (1–A)*(1–B) )
XOR(A,B) = B*(1–A) + A*(1–B)
Not one of those is a digital gate, yet if you are certain of the inputs, they all perform boolean logic.