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The terms digital and electronic are often used interchangeably but I know that it's not correct because something can be digital but not electronic.

Something can be digital in the sense that it's discrete both in time and magnitude.
A picture of a ruler appearing each second is discrete in time because this timing is countable and it's also discrete in value/amplitude/magnitude because it is splitted into countable (in this case, two or more) parts.
A picture like that is likely to be electronic or displayed on an electronic device.

What would be an example of something digital which isn't electronic?
The ruler itself (given all times it appeared in the minds of people)?

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    $\begingroup$ Abacus. Book of tables. $\endgroup$
    – user207421
    May 28, 2023 at 10:44
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    $\begingroup$ Paper punch cards? $\endgroup$ May 28, 2023 at 19:30
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    $\begingroup$ "Electronic" refers to the medium where the data is stored, not the nature (format) of the data. You can store digital data onto any non-digital or non-electronic medium, e.g. writing down the bit stream of jpeg on paper, pressing a CD/DVD, or printing out a QR code, or punch a program onto paper cards. The data is still digital but the medium is clearly not related to electrons. $\endgroup$ May 29, 2023 at 5:12
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    $\begingroup$ relay logic is also discrete and not electronic $\endgroup$
    – Ben
    May 29, 2023 at 23:06
  • $\begingroup$ Baseball could be considered digital, the score by inning has a discrete time basis (t-axis or x-axis) , and the values (y-axis) are always integers. I saw an answer with a scoreboard flipper that was written before my comment. $\endgroup$ Jun 1, 2023 at 17:39

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Boolean algebra? That's not electronic, that's pure math and logic. It can just be and commonly is implemented with electronic circuits, but you can just as well make a logical AND gate with mechanical elements, whether they are cogwheels, or valves with flowing water or air pressure.

In Boolean algebra, there are variables that are either true or false. Statements can be constructed to be true or false, such as is it day or night, does it rain, or is it cloudy.

However, as you already might have seen, just like in electronics, there is always a gray area between day and night, where given a bunch of people they will not all agree on the exact moment when day turns into night or vice versa.

Which means, even electronic circuits are not strictly digital in as even digital logic is implemented by using analog components and circuits.

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  • $\begingroup$ I never learned enough math to get to the algebra part. Is there an example from daily life? From the sapce we may see without light pollution? Perhaps even the universe itself is "digital" in the sense we can count its age and it has countable parts? $\endgroup$
    – somo
    May 27, 2023 at 19:11
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    $\begingroup$ Yes, an abacus is digital calculator. You can count things with it. For some reason I just used two binary states as an example, but all integers are digital. Your fingers are digits too, so digital. $\endgroup$
    – Justme
    May 27, 2023 at 19:25
  • $\begingroup$ I assume that fingers are "digital" because they are discrete in time (exists as long as the person exists, a countable time) and discrete in value (we can count a number, say, five, of fingers). $\endgroup$
    – somo
    May 27, 2023 at 20:37
  • $\begingroup$ Boolean algebra is actually a topic in philosophy. In Introduction to Logic or similarly titled course. Different symbols, but they got truth tables and the same relationship rules including DeMorgan's Theorem. $\endgroup$ May 27, 2023 at 23:13
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    $\begingroup$ @somo Most of all, fingers are digital, because the latin word "digitus" (which is the root of the word digital) means finger. $\endgroup$ May 28, 2023 at 19:54
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Counting with my fingers.

Also when I was a kid in the '60s, all of the adding machines and cash registers were digital and mechanical.

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  • $\begingroup$ If I understand correctly you say that act of counting is "digital" and not necessarily by the number of fingers but by any number. A shopkeeper counting (countable) merchandise (at least once) is a "digital situation"? $\endgroup$
    – somo
    May 27, 2023 at 20:24
  • $\begingroup$ If they're counting, yes. If they're measuring length or weight, no. $\endgroup$ May 27, 2023 at 23:16
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    $\begingroup$ Etymologically correct! $\endgroup$
    – hobbs
    May 28, 2023 at 3:27
  • $\begingroup$ me: spends month cranking out dissertation, 24 updoots in 1.7 years -- rbj: "cOuNtinG wIth mY fiNGeRs", 25 in 6 days -- also your second-highest $\endgroup$ Jun 2, 2023 at 5:48
  • $\begingroup$ I don't get it either. $\endgroup$ Jun 2, 2023 at 5:53
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A scoreboard flipper (or whatever it's called) immediately came to my mind: scoreboard flipper

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  • $\begingroup$ See also my comment on the original post question. $\endgroup$ Jun 1, 2023 at 17:40
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The difference engine and a number of other pre-electronic mechanical calculators are probably the closest to what we consider nowadays digital. And they are, well, pre-electronic.

A mechanical calculator, or calculating machine, is a mechanical device used to perform the basic operations of arithmetic automatically, or (historically) a simulation such as an analog computer or a slide rule. Most mechanical calculators were comparable in size to small desktop computers and have been rendered obsolete by the advent of the electronic calculator and the digital computer.

The abacus is the oldest example that many will recognize, but Pascal's calculator is pretty similar in user experience to a modern day basic calculator, while being entirely mechanical, working by gears and springs.

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The word digital literally comes from the Latin "digitus" meaning a finger or toe, which eventually entered English with both literal and figurative uses. By the 14th century, the word "digit" was used in English with the meaning of a natural and/or whole number up to ten through analogy (people would commonly count things and do minor arithmetic with their fingers). Quite literally, the original digital processing was done on people's fingers in prehistory, and then later in antiquity by written and mechanical devices that modeled fingers. When people counted with fingers, they regarded each of them as either up or down, which also means that digital data is inherently expressible in (or convertible to) a binary format!

The metaphor, then, is that "digital" data is data that can be counted on fingers, or, by extension, expressed exactly in numerals or another format that can be modeled losslessly by a sufficient number of fingers, each of them regarded as held either up or down (and not anywhere in between). That means that "digital" data is more or less synonymous with discrete data.

Examples of non-electronic digital data would thus include:

  • Any data displayed by the holding up or down of various fingers
  • Any data expressed exactly in numbers, such as 3, 55.2, or -0.99
  • Data expressed in any form that has a lossless conversion back and forth to one of the above, such as:
    • Data expressed on an abacus (an ancient digital mechanical calculator)
    • Tally marks
    • True/false or multiple-choice answers on a test
    • Printouts of pre-calculated values, such as times tables, log tables, or trig tables
    • Printed bus and train schedules (e.g. the R2 bus leaves Maple Park Square at 8:03 AM M-F heading northbound toward University Center East)
    • Sheet music
    • All forms of manual signboards that express or encode exact numbers, such as the scoreboard flipper mentioned by Steve
    • Textual information that can be transcribed exactly into a word processor or text editor

Some of the categories above, of course, may have multiple encodings. For example, textual data may be encoded as ASCII, EBCDIC, or Unicode. The critical requirement is that at least one encoding exists which converts both back and forth without loss.

By contrast, the following data would not normally be considered digital:

  • Positions on a ruler
  • Positions on a slide rule
  • Positions on a mercury thermometer, barometer, speedometer, or other physical analog gauge
  • Most forms of graphic art

The above data and their associated devices are considered analog. The mechanical digital calculators mentioned by robert bristow-johnson would contrast with the analog slide rule.

Regarding the music angle, this corresponds nicely with digital versus analog music in the electronic world. A digital representation of music (e.g. an mp3 or a MIDI file) is nothing more than a numerical representation of how to play back the music, in other words, it is an electronic form of sheet music, providing discrete instructions to the computer or player on how to play it back.

Regarding written words and art, the difference is whether it is possible to transcribe exactly. The exact idiosyncrasies of the handwriting are irrelevant to the work. A handwritten novel, for example, can be converted to a text file without loss of any information considered relevant, since the exact form of the handwriting is considered outside of the scope of the novel's content. Calligraphy, however, involves appreciation of the relative positions of the loops, dots, and other forms made with the pen on paper (or other writing medium) and thus a computer transcript does not completely encode it.

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Steve Mould on YouTube built a water computer using siphons that does simple binary addition: Water computer (YouTube)

There's a game called Turing Tumble (Wikipedia) that is a mechanical computer using marbles and can supposedly do anything a modern computer can do given a large enough playfield

Finally, there's an educational toy(?) called Spintronics (Product site) (not to be confused with the field in physics) that allows the construction of mechanical analog circuits. However, Steve Mould showed it could be used to create flip-flops and XOR gates, indicating it could be used to create things like a binary adder: Spintronics (YouTube). There very well could be someone that has done something more elaborate, I just don't have time to try and find it right now

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A telegraph. It is considered as the first digital device, and was so named in 1837. Digital because a finger, or digit, was used to communicate.

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    $\begingroup$ Telegraph used electric current to transfer the signals, so I wouldn't count it as not electronic. $\endgroup$
    – Ruslan
    May 29, 2023 at 9:50
  • $\begingroup$ @Ruslan not by the generally accepted conventions for the terms. Electronic devices are devices which don't require converting electric energy into other forms to function, but are based on the behaviour of the electrons themselves, starting in 1904 with the vacuum tube; the electric telegraph was based on electromechanical relays (digital devices converting electric current to the mechanical motion of a switch) not electronics. $\endgroup$ May 30, 2023 at 11:21
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Perhaps the nearest mechanical equivalent to electronic logic would Fluidics. This is basically hydraulic logic, with no moving parts beyond the fluid itself. The Coanda effect is used to make bistable logic.

Although no logic systems of any appreciable size are built with fludics, a few fluidic components often find their way into the business end of many systems that handle fluids.

Fluidics have the potential to operate at very high temperatures, and in very high radiation environments, so have often been touted as a control method for use within reactors and other difficult environments.

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digital in the sense that it's discrete both in time and magnitude

A gravity swing pendulum clock divides up time in discrete intervals. Through a set of gears the pendulum clock is able to rotate two sticks around the center of a circle. This results in the magnitude, namely, the time of day, as perceived by us with the help of numbers on the circle's perimeter.

https://en.m.wikipedia.org/wiki/Pendulum_clock#:~:text=Each%20swing%20of%20the%20pendulum,rate%2C%20controlled%20by%20the%20pendulum.

A pneumatic player piano energized by a foot pedal is another digital device. Notes and combinations of notes are represented by holes in a paper scroll at regular or non- regular time intervals. https://en.m.wikipedia.org/wiki/Player_piano

There is an electromechanical computer having no electronics. It was built in 1941. https://en.m.wikipedia.org/wiki/Z3_(computer)#:~:text=The%20Z3%20was%20a%20German,of%20about%205%E2%80%9310%20Hz.

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    $\begingroup$ I think that most authorities would call the pendulum clock an analog device because it uses analog means (pointers moving around a dial) to display the time. Even though its hands actually move in discrete steps, that's more of a defect than a feature. If you could find or build a flip-down clock that was powered by a spring or by weights, and was regulated by a pendulum, then that truly would be a digital clock. $\endgroup$ May 28, 2023 at 12:59
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    $\begingroup$ Agree that most of the pendulum clock is an analog device. Some have a cog that by design creates the discrete time units I was referring to. Here's a 10 sec video. videos.pond5.com/… $\endgroup$
    – PaulH
    May 29, 2023 at 6:35
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    $\begingroup$ Not "some." The "cog" in that video is the escapement wheel, invented in 1657. A wheel like that has been at the heart of practically every pendulum regulated or spring regulated clock that's been manufactured since that date. $\endgroup$ May 29, 2023 at 13:46
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The alphabet. Any of them.

Formalized to the point of being "digital" many centuries before electronics ever existed.

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Digital hydraulics. In contrast to classical hydraulic valves, that are proportional ("analog"), digital hydraulics uses a number of on/off valves in parallel to control the flow of hydraulic fluid. It is said to improve efficiency.

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  • $\begingroup$ Or, for that matter, digital pneumatics. Some pipe organs open and close wind chests with a pedal that "seems" analog, but actually opens and closes a few switches that send a binary value to a wind chest that uses bellows and levers to convert a binary-weighted value into a shutter angle. $\endgroup$
    – supercat
    May 29, 2023 at 19:38
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Similar to mechanical calculators mentioned in another answer, the idea has been taken to the extreme to make entire programmable mechanical computers. See my own question on Retrocomputing.SE. To quote the accepted answer there:

While the term mechanical computer may sound not much, the 170 was an unusual beast and maybe the peak of mechanical computing. In 1955 it for sure outclassed all electronic computers of similar or even lager size.

It features one or more 12 digit (decimal) wide ALU and up to 5 result registers per ALU all connected over a mechanical parallel bus.

Programming of the 170 was done by fitting pins into a plug-board.

A program could have up to 53 steps made up one (or sometimes more) of the 90 instructions.

Digital? Check. Non-electronic? Also check. Absolutely fascinating machines.

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To return to the original question, the simplest thing that is not electronic, and digital, would be the die we roll in games, or the coil we flip. Statistically, if the object has n faces, we would expect a good die to give us a probability of 1/n to achieve one of these faces. The next thing is the representation that we have on one of these faces, this might be a number, or some other unique object. So, if we take a coin, and we decorate it with a 0 and a 1, then we get a binary number stream from repeatedly flipping the coin. If we take the die, with 6 faces, and we decorate it with 0,1,2,3,4,5, we would generate a number in this sixfold basis. I am sure there are many other examples, but this is all you really need to get started.

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Strictly speaking, the Bombes of Bletchly Park were electromechanical rather than being electronic, and were about as complex digital technology got before electronics.

The bombe was an electro-mechanical device used by British cryptologists to help decipher German Enigma-machine-encrypted secret messages during World War II.

Each machine was about 7 feet (2.1 m) wide, 6 feet 6 inches (1.98 m) tall, 2 feet (0.61 m) deep and weighed about a ton. On the front of each bombe were 108 places where drums could be mounted. The drums were in three groups of 12 triplets. Each triplet, arranged vertically, corresponded to the three rotors of an Enigma scrambler. The bombe drums' input and output contacts went to cable connectors, allowing the bombe to be wired up according to the menu. The 'fast' drum rotated at a speed of 50.4 rpm in the first models and 120 rpm in later ones, when the time to set up and run through all 17,576 possible positions for one rotor order was about 20 minutes. wikipedia

The USA also made bombes, but those variants employed thermionic valves, the first electronic device. The computers made in Bletchly Park also were valve-based.

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