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Superscalar CPUs and Quantum computing

  1. Mar 1, 2015 #1
    So, from what I understand, modern computers use superscalar CPUs which allows the computer to run two instructions on two separate lines of data in parallel. Which in lame man's terms is just: the CPU can run two instructions at the same time.

    Now, from what I understand, this is also a bragging point for the advancements in quantum computing: quantum computers would be able to compute to pieces of instruction at the same time.

    So what is the difference between a superscalar CPU and a quantum CPU? Am I misunderstanding everything entirely? Is there a twist to the whole quantum computing part? I quite stumped.

    Any and all answers will be greatly appreciated. Hope I posted this in the correct section.

  2. jcsd
  3. Mar 1, 2015 #2


    Staff: Mentor

    The computer I'm using to write this is an Intel i7, that they describe as a Quad Core Duo. That means that there are four "cores," with each of the cores having, in effect, two CPUs. Software that is optimized to run on this machine can have up to eight threads operating simultaneously, each with its own set of data.

    In addition, I have an nVidia video card in my machine whose GPU has 128 "cores" that can be run simultaneously.
    I could be wrong, but I don't think that quantum computers currently exist. And they certainly aren't available commercially if they have been built
    Last edited: Mar 1, 2015
  4. Mar 1, 2015 #3
    Gotcha. But yes, I am aware that quantum computers are not existent. The ones that are are hybrid sort of computers and are owned only by governments and prestigious educational entities. But I've watched videos and such where scientists theorize that a quantum computer would be able to operate several functions at once...but superscalar CPUs already do that. So what do they mean when they assert this?
  5. Mar 6, 2015 #4


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    It is a "hand waving" explanation that we use for non experts, it gives you some idea of why they are faster for certain applications but it is not actually what is happening physically (explaining that requires a LOT of knowledge of quantum mechanics).
    Anyway, if you DO think of quantum computers as being parallel (which again they are not) the key is that EACH element (qubit) can be in a large (actually infinite) number of states at once (superposition) . Hence, whereas the transistors in a classical computer can be either "on" or "off (1 or 0), a qubit can be 1, 0 or any state in-between..

    Note that quantum computers are only faster if you run a suitable quantum algorithm that can exploit the "quntumness" and there are only a few known algorithms that can actually do something useful. Fortunately, some of these can be used to solve important practical problems. However, a quantum computer will never replace classical computer, it would be more like a specialized processor for very specific problems (a bit like the math co-processors that were used 20 or so years ago)
  6. Mar 8, 2015 #5
    I think two issues are being conflated here...

    Firstly "serial" and "parallel" processing, and;
    Secondly "quantum computers".

    When I was a boy, (and yes, we did have electricity...) parallel processing was the great white hope because the rate at which instructions could be executed by a serial processor (something not dissimilar to what was in your average PC until recently), was a fundamental limiting factor. If you could program in such as way as to execute multiple instructions at the same time then the advantage is obvious. Unfortunately in practice this is not as easy as it sounds.

    A good practical example comes from the British code-breaking attempts (at Bletchley Park) during the second world war which used parallel processing. This was so fast and effective at the task it was designed for that it wasn't surpassed by serial computers until the 1990s!

    The UK was at the forefront of parallel computing again in the 1970's when a company called Inmos was set up with the specific aim of producing a fast powerful parallel processing computer. Unfortunately like all good ideas (i.e. Betamax) this was scuppered by cheap chips from the far east which made a British alternative uneconomic.

    As for quantum computers, the probability of seeing one on my desk in my lifetime (which is admittedly a bit shorter than yours) is about the same as being able to travel back in time and make the necessary adjustments so parallel processing wins out!
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