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Question about AM3 CPU on AM2+ motherboard

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March 5, 2011 9:49:27 PM

I am planning to pickup a AM2+ mobo/AM3 CPU combo but I am a little confused. Will I have to change any of my system's specs in order to use a AM3 processor on a AM2+ board (specifically the RAM)?

Here is my current setup:
  • AMD Athlon 64 X2 3800+ 2.01GHz
  • DFI Infinity UltraII-M2 motherboard
  • 2x1GB DDR2-667 memory
  • EVGA GeForce GT 240 512MB GDDR3
  • 400GB Seagate HDD

    (As you can see, I'm really overdue for an upgrade)

    If you want to get an idea of what I am looking for, I was looking at this MSI motherboard:
    http://www.microcenter.com/single_product_results.phtml?product_id=0332148
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    March 5, 2011 10:34:57 PM

    Will an AM3 processor work on an AM2+ socket motherboard?
    Yes, however DDR2 RAM is required rather than DDR3.
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    March 5, 2011 11:13:46 PM

    Honestly I've never been able to wrap my head around what FSB means to the processor.

    What kind of difference in performance does the limited FSB make on a AM3 processor (in layman terms)? For example, if I got a AMD Athlon II X4 640 and installed it on a AM2+ mobo, would there be any significant performance hits?

    Also, if I get a motherboard that says it supports both AM2+/AM3 would I still experience that limited FSB?

    Thanks in advance!
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    March 5, 2011 11:17:59 PM

    Saad073 said:
    Honestly I've never been able to wrap my head around what FSB means to the processor.

    What kind of difference in performance does the limited FSB make on a AM3 processor (in layman terms)? For example, if I got a AMD Athlon II X4 640 and installed it on a AM2+ mobo, would there be any significant performance hits?

    Also, if I get a motherboard that says it supports both AM2+/AM3 would I still experience that limited FSB?

    Thanks in advance!



    Limited FSBs (Front-side buses) generally don't impede performance significantly.
    AM2+/AM3 motherboard logos are simply for marketing, they are AM2+ motherboards.
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    March 5, 2011 11:31:55 PM

    omnisome said:
    Limited FSB (Front-side bus) will not impede performance significantly.
    AM2+/AM3 motherboard logos are simply for marketing, they are AM2+ motherboards.


    That is good to know. But what kind of effect will the limited FSB have?
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    March 5, 2011 11:39:16 PM

    The frequency at which a processor operates is determined by applying a clock multiplier to the front-side bus speed in some cases. For example, a processor running at 3.2GHz might be using a 0.4GHz FSB. This means there is an internal clock multiplier setting (also called bus:core ratio) of 8. That is, the CPU is set to run at 8 times the frequency of the front-side bus: 0.4GHz x 8 = 3.2GHz. By varying either the FSB or the multiplier, different CPU speeds can be achieved.

    A very important principal in overclocking.
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    March 5, 2011 11:48:11 PM

    omnisome said:
    The frequency at which a processor operates is determined by applying a clock multiplier to the front-side bus speed in some cases. For example, a processor running at 3.2GHz might be using a 0.4GHz FSB. This means there is an internal clock multiplier setting (also called bus:core ratio) of 8. That is, the CPU is set to run at 8 times the frequency of the front-side bus: 0.4GHz x 8 = 3.2GHz. By varying either the FSB or the multiplier, different CPU speeds can be achieved.

    A very important principal in overclocking.


    Well that sounds like it would have an effect on performance. If for example I had that Athlon II X4 640 CPU, it's FSB is 4000Mhz and its clock speed is 3.0GHz. So if the FSB was limited to 2000Mhz, wouldn't that affect the clock speed?
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    March 6, 2011 12:34:44 AM

    omnisome said:
    Will an AM3 processor work on an AM2+ socket motherboard?
    Yes, but the FSB frequency of the CPU will be limited to 2000MHz

    Are you sure it's 2000mhz?
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    March 6, 2011 12:39:30 AM

    kilo_17 said:
    Are you sure it's 2000mhz?


    lol
    My bad, was thinking of something else.
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    March 6, 2011 12:40:59 AM

    With a 640, it would be 200x15 (multiplier for said CPU) = 3000mhz clock speed.

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    March 6, 2011 1:19:08 AM

    Ah okay. So there would be no issues then right?
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    March 6, 2011 1:38:11 AM

    Shouldn't be. If you use a 640, then it should have no problems running at 3ghz.
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    March 6, 2011 1:48:52 AM

    omnisome said:
    Will an AM3 processor work on an AM2+ socket motherboard?
    Yes, however DDR2 RAM is required rather than DDR3.


    Wait when did you change your answer Omnisome? Anyway, I do have DDR2 and from the research I have been doing over the past few hours it seems like as long as the motherboard supports it then it should be fine.

    Also, thanks kilo_17 for clearing up the confusion. I was worried there for a second! lol How have you been enjoying the 640?
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    March 6, 2011 2:04:25 AM

    I like it! It's a good multitasker, atleast for me. Today I had an AVG scan running, Spybot Search and Destroy scan running, AMD Overdrive and HWMonitor open in the background, while I was playing DiRT 2. For a casual user like me, it's handled everything I've needed it to do. I honestly see no need to overclock it, it can keep up with everything. And at around 100USD, I think it's a great CPU. Also, at stock speeds, the stock cooler works fine for me. (But I do have two case fans)
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    March 6, 2011 2:58:03 AM

    kilo_17 said:
    I like it! It's a good multitasker, atleast for me. Today I had an AVG scan running, Spybot Search and Destroy scan running, AMD Overdrive and HWMonitor open in the background, while I was playing DiRT 2. For a casual user like me, it's handled everything I've needed it to do. I honestly see no need to overclock it, it can keep up with everything. And at around 100USD, I think it's a great CPU. Also, at stock speeds, the stock cooler works fine for me. (But I do have two case fans)


    That's awesome. The price really impressed me and the feedback I've read from everyone has been really positive. I think I'd rather go for this than a dual core Phenom at the same price lol
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    March 6, 2011 12:29:24 PM

    Yeah, if I were in that situation I think I would take the 640 too. I mean, with the Phenom, it's clocked 300mhz higher, has an unlocked multiplier, and the 6mb of L3 cache, but the Athlon has double the cores. Those extra cores on the Phenom aren't guaranteed to unlock, plus you need a core-unlocking board. Keep in mind this is my opinion, and I'm not trying to tell you which one to buy.
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    March 6, 2011 3:50:35 PM

    As of this post the 640 is 5USD more than the 645 on Newegg. I'm not sure about the performance difference, but with that chart, if you compare the 640 and 645, the 640 doesn't come far behind the 645 in most of them. Or you could always bump the 640 up a couple hundred megahertz lol. But that's just my opinion, you can do whatever you want.
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    !