Very noob question...

Discussion in 'Mac Basics and Help' started by Sam Yikin, Apr 29, 2008.

  1. Sam Yikin macrumors regular

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    #1
    I don't really know much about how processors work, and a friend recently made a claim that I'm not sure about. He said that a 3GHZ dual core processor actually means two 1.5GHZ cores. I have almost no idea about this subject and would like to know if this is true.
     
  2. dukebound85 macrumors P6

    dukebound85

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    #2
    means 2 cores at 3ghz apiece

    doesnt add up to 6ghz in total speed though as there are other factors to consider
     
  3. richard.mac macrumors 603

    richard.mac

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    #3
    yep just means what it is, a 3GHz processor with 2 cores. you dont divide the clock speed by the number of cores to get the clock speed per core, its just a 3GHz CPU with dual cores.

    i think these days too much emphasis is based around the clock speed when CPUs are getting up to 4 cores. some people will go for a Pentium >3GHz single core CPU rather than a Core 2 Duo 2GHz dual core CPU as they think its faster but having dual cores means you can compute twice as many processes as a single core. this is the megahertz myth.
     
  4. Sam Yikin thread starter macrumors regular

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    #4
    Let me get this straight...

    So a 3GHZ dual core means that it's a processor chip with two cores, EACH CORE runs at 3GHZ, but this does NOT mean that both of the chips total up to running at 6GHZ?
    I'm assuming, at a basic level, that this is because they are two seperate cores, and thus the dual core fuctionality is more useful for multitasking?
     
  5. spinne1 macrumors 6502a

    spinne1

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    #5
    Imagine a farmer plowing a field (single core). Now imagine another farmer showing up and plowing the row next to the first farmer (dual core). More work gets done with two farmers but each individual row is not being plowed at twice the speed (thus a dual 3Ghz is not 6Ghz), but twice as much work is being done. This is similar to the effect dual core has over single core.
     
  6. robbieduncan Moderator emeritus

    robbieduncan

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    #6
    But (and this is why you can't add them together) the two farmers cannot plow a single furrow together, so the time to plow a single furrow is unchanged.

    So in software terms a single thread of execution still runs at 3Ghz, but there can be another thread of execution also running at 3Ghz. Fortunately OSX and a lot of the applications on it are heavily threaded...
     
  7. skunk macrumors G4

    skunk

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    #7
    However, the time to plough two furrows is halved...
     
  8. robbieduncan Moderator emeritus

    robbieduncan

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    #8
    Indeed. I was adding to the original post which implied this. I was trying to point out that a single threaded executable (lots of games apart from very modern stuff for example) won't gain from this as they are the single furrow...
     
  9. eXan macrumors 601

    eXan

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    #9
    lol nice analogy :D

    A dual core processor clocked at 3 GHZ has 2 cores that are 3 ghz each.

    Applications written to take advantage of having additional cores will be faster (quite often they are roughly twice as fast on 2 cores vs 1), while those that aren't will still run at 3 ghz.

    Most CPU-intensive apps now take advantage of at least 2 cores and Mac OS X is extremely good at splitting the duties between the cores so in most cases having more than 1 core is very good.
     
  10. timsutcliffe macrumors 6502

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    #10
    Nice

    This was something i've never understood either, so thanks for asking the question. And thanks for the answers as well, nice analogy.
     
  11. scienide09 macrumors 65816

    scienide09

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    #11
    I like the analogy as well, and the teamwork that went into bringing it together. I think I will start using it to explain this difference to friends who have asked me about it.
     
  12. patrick0brien macrumors 68040

    patrick0brien

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    #12
    Another I use in consulting is:

    "The speed limit is the same, but the road twice as wide."
     
  13. Sam Yikin thread starter macrumors regular

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    #13
    Thanks for the replies. These were very helpful to me in learning how my new iMac is going to work. However, my friend is 100% certain that his 1.8GHZ Core 2 Duo Inspiron laptop is actually two cores running at 900MHZ each. He claims a tech support rep at Dell told him this. Could he be right, or did Intel never make a processor like that?
     
  14. robbieduncan Moderator emeritus

    robbieduncan

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    #14
    No he's not right. If the CPUs are not under load (i.e. not busy) they will clock down though. So at some times they may run at 900Mhz (to save power), but when they need to both will run at 1800Mhz.
     
  15. patrick0brien macrumors 68040

    patrick0brien

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    #15
    -Sam

    You're friend either made it up, or was given bad information.
     
  16. mactastic1971 macrumors regular

    mactastic1971

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    #16
    Using the same analogy, another point to bear in mind...

    Get the 2 farmers plowing one field, starting from opposite ends and the field gets plowed quicker but not 2x quicker.

    Why? Theres only one plough and the farmers are sharing it over the entire time to do the field ... the plough is the kernel !!!
     
  17. ChrisA macrumors G4

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    #17
    Your friend is wrong. It's that simple. Each core runs at 3GHz.

    But really it is not so simple. having 2 CPU cores does not mean the computer is twice as fast. Here is the dreded car analogy.. Having two cores is like owning two cars. You do not get to work in half the time but assuming you have enough drivers in the family people can get to about twice as many places per day but nobody gets there any faster.
     
  18. deputy_doofy macrumors 65816

    deputy_doofy

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    #18
    As others have mentioned, it is possible that the cores throttled-down for power-savings, thus reducing each core to about 900MHz. Just to clarify, Intel/AMD/IBM have never made a "dual core" chip where the 2 cores are added up to give the final GHz rating. Your friend does have bad info.
     
  19. Tallest Skil macrumors P6

    Tallest Skil

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    #19
    That's why he's wrong.
     
  20. ChrisA macrumors G4

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    #20
    I like the polygamy example better. Having two wives does not mean you get a baby in four and a half months.
     
  21. robbieduncan Moderator emeritus

    robbieduncan

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    #21
    The OSX kernel is quite well multi-threaded: it can and does spread itself across CPUs (or cores) quite well.
     
  22. mactastic1971 macrumors regular

    mactastic1971

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    #22
    I agree - but there is a finite amount of time where at least one of those CPUs is doing 'non farming related activities' (system work) at any one time so thats how you can never get to 2x.
     
  23. thejadedmonkey macrumors 604

    thejadedmonkey

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    #23
    However, Intel is working on a chip that will allow one core to overclock while slowing down the other one.

    In other words, they are working on a plow that will expand if the 2nd plow isn't doing anything.:p
     
  24. eXan macrumors 601

    eXan

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    #24
    Thats not due to kernel being single-threaded, but due to particular application not multithreaded.
     
  25. Sam Yikin thread starter macrumors regular

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    #25
    Thanks guys, I'll show him this thread and see if that changes his mind. I DID try to tell him that maybe it was his laptop scaling down to 900 MHZ to save power, but he refused to believe me (not sure why).
     

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