Brass Tacks and Comparability

So I thought I should try to explain “comparability” very simply. Reading my previous posts, which were derived from larger texts, I spend a lot of time saying a lot of generalities, and I think the main point is getting missed. So here’s me getting down to brass tacks on the subject.

A computer CPU is a very basic electrical device. Send it a stream of electrons and a command to “add”, and it returns another stream of electrons representing a purely “mechanical” (i.e., unintelligent) electrical result. That CPU doesn’t know anything about semantics, or whether the switches and gates it opens and closes should appropriately be applied to those particular data streams. It just does what it was designed to do given that particular sequence of electron streams. If the streams are comparable before they get to the CPU, then the output will be meaningful. If they are not comparable, then the output (and being a CPU, there will be some output) will not be meaningful.

So the job of the software is to manipulate each symbol before presenting it to the CPU. In particular, the software needs to take each symbol and replace it with one that MEANS the same as the original symbol, but which will present itself to the CPU as COMPARABLE to the other symbols.

Comparability has to be put into the computer, through the software, by a human being. In particular, it is the human who understands when one data stream is not comparable to another, and it is the human being who writes the code to change one stream so that it becomes comparable to the other.

So what really are we talking about? Let me make a non-computer example to show the point.

2 + 00000010 = IV

If I take a pencil and write the above string of characters on a piece of paper, and show it to another computer programmer, after a few moments, I would expect that person to agree that this is a correct mathematical statement

 two plus two equals four

Part of the success of the person in understanding the original statement is that they are able to parse each symbol in the string, interpret the MEANING of each symbol, then translate each into COMPARABLE numeric ideas.

If the computer CPU could experience each symbol as I’ve written it (let’s agree that each of the symbols depicted here would have similar diversity of structure in the computer as they do here on the page), then we can immediately grasp what comparability is. The CPU does not know what the symbols mean, it cannot make the interpretation just by looking at the symbols as they are presented and come to the same conclusion as the human. 

If we look at what I, the human did, to provide you, the reader, with a more readable version of the equation, I replaced each symbol with another one that meant the same, but which appeared as mutually comparable symbols:

  • 2   –>  two
  • +  –>  plus
  • 00000010  –>  two
  • =  –>  equals
  • IV  –>  four

Before the CPU can compare the symbol “2” to the symbol “00000010”, they must both be replaced with two other symbols, each with the standard interpretation of “two”. These new symbols must be structured to flow through the CPU in such a way that their very structure is modified by the CPU to create a third symbol whose standard interpretation has the meaning “four”. The “plus” symbol must be translated into the CPU’s “ADD” instruction, and the “equals” symbol is represented by the stream of electricity leaving the CPU with the resulting symbol.


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