Why Does Activity Monitor Show 4 CPUs?

Discussion in 'MacBook Air' started by jason.siegel, Jul 22, 2011.

  1. macrumors 6502

    Joined:
    Jun 15, 2011
    #1
    Why does Activity Monitor (and iStat) show four CPU cores? Isn't the new Air dual-core?
     
  2. macrumors newbie

    Joined:
    Jul 21, 2011
    Location:
    USA
    #2
    Hyper-threading. Each core can run two threads at once.
     
  3. macrumors P6

    Intell

    Joined:
    Jan 24, 2010
    Location:
    Inside
    #3
    They are dual core. But each core has two virtual cores.
     
  4. thread starter macrumors 6502

    Joined:
    Jun 15, 2011
    #4
    I'm not familiar with the vocabulary, apparently. Is that similar to how one CPU can double its workload with two cores? So now each core can double its workload with two threads?
     
  5. macrumors 604

    wordoflife

    Joined:
    Jul 6, 2009
    #5
    Each core has two virtual threads.

    The computer thinks that you actually have four cores (2 cores X 2 threads for each processor), so that's how it sends the data. But in reality, it's really being processed by two individual cores.
     
  6. thread starter macrumors 6502

    Joined:
    Jun 15, 2011
    #6
    Interesting. What's the advantage of hyper threading?

    Thanks.
     
  7. macrumors 601

    clyde2801

    Joined:
    Mar 6, 2008
    Location:
    In the land of no hills and red dirt.
    #7
    Okay, let's try this analogy old school. It's like having a four barrel carburetor. You can chug around for most of the day on two and be fine, but if a program needs maximum performance across multiple cores, the cpu can open all four up. They're there if you need them, and sit there quietly if you don't.
     
  8. macrumors 604

    wordoflife

    Joined:
    Jul 6, 2009
    #8
    It only helps to a certain degree depending on how the application is coded. Basically it has improved support for multi-threaded code, allowing multiple threads to run simultaneously, improved reaction and response time. (via Wikipedia).

    It's not really a big performance difference, but that explains why it is showing 4 cores.

    This video will help you picture how this is set up: http://www.youtube.com/watch?v=kkrqyEpINSQ
    In the video, the processor is a quadcore processor with hyperthreading (so it shows 8 threads) but you'll get the point on what is going on.
     
  9. thread starter macrumors 6502

    Joined:
    Jun 15, 2011
  10. macrumors 601

    sammich

    Joined:
    Sep 26, 2006
    Location:
    Sarcasmville.
    #10
    Each core can only do a single task at any given time, and usually the task doesn't use all the power of the processor when that task is occupying it. There's also a small 'lag' as the processor changes tasks. With those two things in mind, having 2 virtual cores per physical core means that the core (man, I hate repeating the same word so many times) won't be sitting idle as much since two tasks can be running at once. And finally, those two tasks can be done without changing tasks back and forward all the time.
     
  11. macrumors 68030

    waloshin

    Joined:
    Oct 9, 2008
    Location:
    in my world.
    #11
    Each cpu has one virtual thread per core not two.

    If each cpu had two virtual threads per cpu you would see 6 cpu's and not 4.
     
  12. macrumors 601

    HiRez

    Joined:
    Jan 6, 2004
    Location:
    Western US
    #12
    Ah, so that's why MenuMeters is showing me 4 CPU graphs.
     
  13. macrumors 601

    sammich

    Joined:
    Sep 26, 2006
    Location:
    Sarcasmville.
    #13
    Same thing, different way of looking at it. At least, the way I see it, the actual core is masked by the two logical/virtual cores.
     
  14. macrumors 6502a

    hachre

    Joined:
    Sep 26, 2007
    Location:
    Munich, Germany

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