The word, analog, is commonly used to describe a system that predates digital computers. I blink each time I hear it because I know it is not right. Formal definitions in computer science are better. They contrast analog and digital by how they store data, continuously or discretely. The terms are treated as opposites. I still blink. If the formal definition is correct, the dyad should be digital and continuous. I will explain how analog and digital are not exactly opposites.
In analog telephone lines, the fluctuations of the voice correspond to the electric vibrations in the wires. The essential waveform is preserved. In a digital voice system, the voice transmission is encoded into bytes for transmission, and later decoded back into sound. All digital computers do the same. Electricity flows through switches, representing data in binary digits, one or zero, called bits. So far so good, but as above, the dyad should be digital and continuous.
An analog clock measures time by the continuous motion of one or more hands. In a digital clock, an electric charge is passed through a crystal, causing a sound whose frequency is converted into counts of seconds and minutes and so. The digital aspect is seen in the display of number of hours, 1-12 or 24. The base 12 or 24 system is as digital as binary. But then, then hands of an analog clock also point to the same digits. The clock is both analog and digital.
Today, analog is used as adjective, but originally it was a noun, a comparison of one thing to another. For example, a pump is an analog of the heart. An analog is a literary device with properties. One property is proportion, a correspondence in size or quality between one thing and another. An analog can be exactly proportional to the original. If I mark the length of my finger on a ruler, the marked ruler is a one-to-one analog for the length of my finger. I can use the ruler as a record of my finger length at a particular age and compare the size again in the future.
More often, the proportionality is at a scale. A map is an analog for a real world geography, reduced in scale for analysis and portability. This bring out a second property of analogy, incompleteness. Analogy is a comparison such as a metaphor or simile, which are substitutes. My love is not literally a red red rose. A map is not literally the land. Even if I map the world with a high resolution satellite camera I cannot record every detail. This fact is what makes the map useful. By omitting detail the map becomes something I can see at a glance, measure with a compass, and carry in my pocket. But what happens when I zoom in with a magnifying glass? It depends on how the map was printed. I may see dots. A color map has a range of dots. A black and white map has two types, black or not — binary digits, bits, digital. Even a hand-drawn and painted map is not continuous like the real world. The resolution of analog is always digital.
The third property of the analog is its purpose, to explain a new or complex idea with a familiar one. We use analogy to help explain and understand. It is the same purpose for a digital representation. The bits must ultimately correspond to something meaningful in the world. Bits mean nothing without a mapping to numbers and characters and real world phenomena. A ruler represents my finger. A clock represents time. Ones and zeros decode back into voice, and images, and music.
Decoding depends partly on the continuous physical form in which the data was stored. Take language. In some ideal language we could map all the forms of a word to a single lemma. We could also strip out all punctuation and spacing. In real language each form carries unique differences in meaning that must be preserved in digital storage. Punctuation and spacing also meaning. All digital systems that store text also store these real world features. Digital systems require analog data.
Analog and digital are not precise opposites. Analog has an older literary meaning that still applies, comparison. My discussion of the properties of proportion and completeness showed that the analog always resolves to the digital. Also, the purpose of analog is just as applicable to the digital. None of this analysis will make a whit of difference to the operation of analog or digital systems. The analysis cannot be used to claim that analog technology is superior to digital. The main benefit is that I might stop blinking the next time someone misuses the terms analog and digital.