So why...

Discussion in 'Macintosh Computers' started by iGary, Mar 25, 2005.

  1. iGary Guest

    iGary

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    #1
    Does the PowerMac G5 require that RAM be installed in pairs, and the iMac G5 does not? :confused:
     
  2. hcuar macrumors 65816

    hcuar

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    #2
    I think it's because the PM G5 requires dual channel memory... It's a feature in the iMac that is optional.

    That being said, I'd imagine that the dual processors split the banks.
     
  3. iGary thread starter Guest

    iGary

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    #3
    The single processor PM models must be installed in pairs.

    Does this mean that the G5 in the iMac is not a 64-bit processor, or the architecture is different?
     
  4. Lacero macrumors 604

    Lacero

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    #4
    That's one of the reasons I still have the original 2 128MB RAM Dimms in my PM G5. I'm waiting for the price of 1GB Dimms to drop in price in line with the 512MB versions before I upgrade the RAM.
     
  5. iGary thread starter Guest

    iGary

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    #5
    Yeah, I just checked Crucial on their G5 2.0 RAM prices and 4 sticks of 512 runs about $240.00.

    I'm thinking for my Photoshop batches, that should be fine. I can always add more later. I have 2.0GB in my PM G4 now and it works great.


    BUT

    Why no pair requirement in the iMac G5?
     
  6. hcuar macrumors 65816

    hcuar

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    #6
    I think the single G5 PM still requires the setup to be dual channel. The iMac doesn't require a dual channel configuration. I've seen the same in PC motherboards... Some require dual channel, some have it as an option.
     
  7. iGary thread starter Guest

    iGary

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    #7
    Yes, the single-processor PM's require pairs of RAM as well.

    I'm just curious why the iMac doesn't, and further to that, why the iMac G5 is so much slower aside form FSB speed...I mean my PM G4 does just as well as my iMac G5 at work (OK, the G5 is a little speedier, but not by much).

    Is there a chance that this iMac chip is not 64-bit - is dual memory a 64-bit issue?
     
  8. hcuar macrumors 65816

    hcuar

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    #8
    No... not a 64 bit issue. One and only one reason. Cost. Period. Only need one DIMM rather than 2.
     
  9. iGary thread starter Guest

    iGary

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    #9
    Hokay.

    Just curious. :D

    Not an architecture person.
     
  10. TIGERmac macrumors member

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    Nov 12, 2004
    #10
    The speed difference between a SP 1.8 GHz PM and a 1.8 GHz iMac G5 isn't that great. For everyday tasks, the G4 is probably as quick as a G5...this isn't unique to the iMac. Throw in a few processor intensive tasks and the G5's extra horsepower becomes apparent, however.

    G5's rock. :)
     
  11. jsalzer macrumors 6502a

    jsalzer

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    #11
    Half the something

    Hey, Gar,

    I read somewhere that, with the iMac G5 (which I have), that both modules need to have the same kind and amount of RAM for the iMac to do somethingorother important to its full potential. If you have two different sticks, you get half the whatever.

    I don't recall exactly what it was, but I remember it sounding important enough to me that, when I ordered, I got a single 512 so that I could add another 512 when I can afford it, rather than going 256+512 like I originally planned.
     
  12. Chaszmyr macrumors 601

    Chaszmyr

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    #12
    The answers to these questions are quite simple.

    First of all... The PowerMacs have dual channel RAM, the iMacs do not. This has absolutely nothing to do with 64 bitness, the iMac G5 is definitely 64 bit. Dual channel RAM is just faster... It's kinda like dual processors, except for RAM instead of CPUs. Cost isn't the real issue, I don't think.. Because in the PC world there are motherboards that have the option of using dual channel RAM, but don't require it.

    The PowerMac also makes better use of dual channel RAM than an iMac would because not only a faster system bus, but also a dual system bus in the dual processor models. The speed gain from dual channel RAM is relatively minor, but it's better than no gain at all on a performance system.

    Next the speed issue. I don't know what G4 you're comparing the iMac G5 too, but the iMac G5 is definitely faster than a fast G4... but not much faster. Part of it is because a 1.6ghz G5 isn't really much faster than a 1.5ghz G4 for most things, for some things its not even quite as fast. Another reason that the iMac G5 isn't faster than it is is because Apple crippled the FSB. If I were to speculate, I'd say they crippled the FSB for heat reasons.
     
  13. hcuar macrumors 65816

    hcuar

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    #13
    Umm... actually the G5 iMac has the same bus speed as the single processor PM. Single processor G5s have a bus speed equal to 1/3 of the processor frequency. Dual processor G5s have a bus speed equal to 1/2 of the processor frequency. I don't think it's a heat issue otherwise the single processor PM would have a faster bus speed. I'm wondering if the single processor G5s use chips that aren't top in their quality rating so they scale back the FSB. Just a thought. Apple could also be putting in an artificial barrier to their product lines to prevent a single processor system from keeping up with their dual counterparts. :rolleyes:
     
  14. Platform macrumors 68030

    Platform

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    Dec 30, 2004
    #14
    On my PC I have the option of Dual Channel RAM but it is not a requirment ;)

    I'm using 2x256 but I don't need, just a bit better performace ;)
     
  15. auxplage macrumors 6502

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    #15
    The original, Single 1.6 and 1.8 PowerMac G5s used a FSB equal to one half of the processor.
     

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