What Is A Computer?

What is a computer? You’d think that would be a fairly simple question. After all, I’m using one to type this up, I ought to know what it is, right? I mean obviously, it’s a…computer! I mean, it’s got a keyboard, and a monitor, and there’s that box down there…

But what is it that makes all that stuff a computer? Why do we look at it and go, “Oh yeah, that’s a computer,” as opposed to, say, “Oh, that’s just a TV,” or “That’s where I keep the leprechauns at night.”?

Some people try to define the word “computer” just by saying “it’s got such and such parts and they all work this way,” but that’s like saying “airplanes have two wings and jet engines.” It’s true, but I could build an airplane that didn’t have two wings or jet engines. The way something works is not a definition for that thing.

Others try to define it mathematically, but that can also be somewhat limiting, because then only the devices that fit into your mathematical scheme are computers, and there are multiple mathematical models that would all be considered “computers.”

So I turned to the dictionary. That was fun for me–I’m a dictionary fanatic. I’ve got lots of great dictionaries, and there are even more online. The Compact Oxford English Dictionary had the best definition, as it turned out.. I was very happy with it at first, but when I started to think about it, it didn’t quite work. For example, it calls computers “an electronic device,” and we know that computers can be built without electronics.

So I worked to come up with a definition of my own. Strangely enough, the key question that it boiled down to was “Why is a player piano not a computer?” It “processes information” by playing notes from its roll. If you gave it an etching machine, it could “store information” back on to the roll. But despite all that, it’s clearly not a computer. What is a computer doing that is fundamentally different from a player piano, that a player piano could never do?

After about two years, I finally came up with an answer that was both simple and all-encompassing. A computer is:

Any piece of matter which can carry out symbolic instructions and compare data in assistance of a human goal.

And that, my friends, is really it. My only thought left is whether I should say “a series of symbolic instructions” to more clearly differentiate it from a calculator. What do you think?



  1. I like your definition. Personally, I would use “a series of”. One thing: why do you treat ‘comparing data’ in a special way? Shouldn’t it be included in the ‘carry out symbolic instructions’ bit?

    • Because that’s the key bit that separates it from a player piano. A player piano can follow symbolic instructions in assistance of a human goal, but it can’t compare two pieces of data, whereas a computer can.


  2. Great read, Max!

    My only concern is that, to me, a calculator is in fact a computer; It takes a set of instructions (this + that * widget to the Nth power) as input, and produces a result in assistance to my own person goals. It becomes an even better computer when I am able to modify its logic and interpretation of input, to produce even more useful assisting results that the original could not. ๐Ÿ™‚


    • Thanks! Well, a graphing calculator is definitely a computer. I’m just not sure that something that only provides instantaneous output to one command (like a very simple calculator) is something that we should consider to be a “computer”. It’s kind of hard to say, though–that’s a bit of a gray area. ๐Ÿ™‚


  3. Your TV is probably running a firmware that is a series of comparison, branches and symbolic instructions. I think that the main differentiation for a computer now is the ability to run different applications, one can watch movies or TV, then start to typing just to then read the latest news on a website and for a break play a little game.

    • Yeah, that’s usually the definition of a general-purpose computer. I’d still say the firmware inside the TV is a computer, though. It’s just that a TV could be built without involving a computer at all, even though modern ones aren’t.


  4. Why the “piece of matter” part? Why not just “Anything”? You’re not really excluding anything except for maybe optical signals or other massless particles.

    And what’s your beef with a player piano? I’d certainly consider it more of a computer than a well trained rat, but a well trained rat (or a lackluster employee) could definitely fit your definition.

    • Hmm, you’re right, I could probably say “an object” or “a piece of matter or energy.”

      A well-trained rat could fit the definition, but it also may have some degree of volition, so it could possibly go beyond the definition as well. But I agree that a living thing could be reduced to being a computer by that definition. It’d be a sad thing, but people have certainly tried to do it to people before.


  5. I like it, but i would agree that “structure” is probably more appropriate than “chunk of matter.” I mean, what happens when we start using pure energy? Or if the universe is actually a hologram. Also, what, are you biased against aliens? “in assistance of a human goal.” You’re the guy that’s going to be responsible for our eventual enslavement to the alien overlords ๐Ÿ˜‰

    And, since I’m ranting anyway, if you wanted my complete description (and it’s a free internet, so you’re going to get it) “A structure that can manipulate arbitrary information arbitrarily.”

    • Yeah, “structure” might be more appropriate. Or maybe “device?” That makes it more generic, I think.

      Hahahaha, yeah, I’m totally biased against our alien overlords, obviously. ๐Ÿ™‚ There’s not a very good word to put there that most people would know. “A sentient goal” or “A volitional goal” would be close, but perhaps not quite accurate.

      And thanks for your complete description, I always like to see what other people come up with. ๐Ÿ™‚


  6. If you like dictionaries, here’s what the Oxford English Dictionary says about it:

    (removed to comply with OED Online license)

    • Thanks! ๐Ÿ™‚ I’m a big fan of the OED, but I don’t have one at home and I don’t have a subscription to the online one. I do have a nice copy of Webster’s Third New International, though, which I’m pretty fond of.

      Are you sure there’s no copyright issue with reproducing a whole entry from the OED like that, though?


      • Actually I didn’t think about that … After all it is just a single entry … Now that I read the license terms I see that it is not allowed to “display or distribute any part of OED Online on any electronic network, including without limitation the Internet and the World Wide Web (other than the institution’s secure network, where the Subscriber is an institution);”. I can’t tell though if they really meant this to apply to single entries, or it’s just a protection against copying the whole dictionary.

        • Hmm, that sounds like it was meant to apply to single entries, and OED entries are so long that reproducing a whole one is probably beyond “fair use”, too (though I don’t know). I’ve removed the text for now.


          • Try the American Heritage Dictionary of the English Language instead. It tends to have the most precise definitions of any general purpose English dictionary I’ve come across, and the use terms at its Important Information page explicitly provide an exception to the copy prohibition where “such use is expressly permitted by applicable law.” In short, it doesn’t try to circumvent fair use.

            The definition of computer in the American Heritage Dictionary is, in my humble opinion, a darned sight better than the OED’s. AHD says a computer is:

            A device that computes, especially a programmable electronic machine that performs high-speed mathematical or logical operations or that assembles, stores, correlates, or otherwise processes information.

            That was definition 1. Definition 2 is actually the definition that preceded modern usage, of course, and from which our current understanding of the term derived:

            One who computes.

            Automated electronic computers were essentially invented to replace people who performed tedious calculations all day, after all.

  7. Humans and all living creatures are biological computers. Hmm, that’s a nick definition. Living = Biological Computers; This definition will surely change as robots get power, but still, there must be a classification for biological computers.

    Anyways, I say that a computer is anything that can collect data though input devices, and release output after processing it. Processing involves logic, otherwise known as if then (and while) conventions. Pianos only have one output for each input, meaning it doesn’t process the data, as it can’t make any choices.

    Computers collect input, logically use the input, and release output. Humans are very complex computers in that the main source of output (thought) is also input for the next operation, and that we have many parallel thought streams at once all vying for power. Still, our lives are mechanical. It’s just so complex that we cannot mechanically and scientifically deduce our next thoughts though simulations.

    • Player pianos translate symbols into sound, which is processing data, by the definition of processing. It’s not comparing, though, which is why the word “comparing” shows up in my definition.

      The primary difference between a person and a computer is that a person has volition. It is possible for a human to make a decision without any input whatsoever.


      • Oh, have I been using the word process wrong. ๐Ÿ™ Okay, change the word process to compare in my definition…

        Please note that nothing can make a decision without input. At the minimum, it has to be based on chance, but it can also be based on reading memories stored in the brain looking for truths that may have been hidden to you. Even when you are first born, you have input.

        • Mmm, I’d disagree with that. I could theoretically make any decision I wanted right now, without limit. I could conceive of something that I’d never seen, that was not a composite of past memories, and make a decision about it. Most people don’t do this, but a person is capable of doing so. This is usually what we call “creativity” (though many people are also creative by compositing past experiences).

          Also, on the other side, I’m free to make decisions that don’t conform with my input or instructions–something a machine is incapable of doing.


          • You could make any decision, as long as you have the thought to do it. You cannot create something that isn’t a composite of past memories. You can take all the small parts of paste memories, and bend them around. Creativity is merely the ability to mesh and destroy ideas until you found a useful one.

            Yes, you are free to make decisions that don’t conform with your input. Either your thought process is bad (glitchy) or you made the conscious choice to say “ignore that”, which makes humans even more complex. Humans are computers…very complex computers…we have no free will, but we have the ability to do complex tasks we haven’t yet learned to code into electronic computers yet.

          • I think Ryan put it well. Who or what we are is constituted by what we have been. Our experience of the past, however long you wish to make it (Too philosophical to go there)defines us. Of cause variable are too many to comprehend, but if we can do it, we can predict exactly what one will do or say in the next second. So, it is a computer, a very complex one.

      • In the strictest sense, a player piano does an 0/1 comparison. There is either a hole/symbol etched there or there is not. This determines whether or not a sound is played. Where the hole is placed determines the pitch. The space between holes determines the speed. Without the ability to compare, you would always have constant sound, or no sound at all.


        • That’s true, actually, and a really good point. ๐Ÿ™‚ What a player piano can’t do is read, store, and later compare two separate pieces of data that it read at separate times, though. I suppose that’s more along the lines of what I meant.


    • Sure, or just one who computes without a machine, too. ๐Ÿ™‚ I’m pretty sure that people are theoretically capable of doing any work that a computer does, though they probably wouldn’t want to do a lot of it! ๐Ÿ™‚


  8. A Computer is a programmable machine and it has two prncipal characteristics such as: responding to instructions in well manner, execute prerecorded list of instructions.It is a machine that calculate caliculations and manipulates data according to a list of instructions

  9. What is computers anyway?

    I need answers, the clearer one…

    you see I’m working on research works about computer..
    I have a hard time usually understanding it too..

  10. computer is the most important things in our life… so we human can’t live with out it, we a lucky that we got this technology that can catch anythings in this world……

  11. “only the devices that fit into your mathematical scheme are computers, and there are multiple mathematical models that would all be considered โ€œcomputers.โ€”

    Umm, no. Insofar as there are multiple mathematical models (viz., recursive enumerable functions, Turing machines, and Lambda calculus), they have been proven equivalent. I know of no mathematical definition of a computer that exceeds the computational power of these and no less definition that is considered to be a computer.

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