6 Replies Latest reply on Jan 14, 2012 9:08 AM by adilhussain21

    Quad channel cpu's lower bandwidth then triple channel?!?!

    kwhubby

      I am looking at the intel cpu comparison chart: http://www.intel.com/content/www/us/en/processor-comparison/comparison-chart.html

      and I am a tad confused at the maximum memory bandwidth of i7-9xx versus the 2nd generation i7's. I notice on the 4 memory channel and 2 memory channel cpu's a posted bandwidth of 21GB/s, while the 3 memory channel cpu's show 25.6GB/s

      Why is this so? Is 4 memory channels a lie-or did the memory controllers lose half the bandwidth? What gains is there to 4 memory channels with these specs?

        • 1. Re: Quad channel cpu's lower bandwidth then triple channel?!?!
          Adolfo_Intel

          I am not sure where you are seeing that information, please provide me a link where you are actually seen those numbers.

          Also if possible please provide me 2 processor models that you have on your mind, so I can compare them.

          • 2. Re: Quad channel cpu's lower bandwidth then triple channel?!?!
            kwhubby

            Ok, go to http://www.intel.com/content/www/us/en/processor-comparison/comparison-chart.html

             

            Select the following cpus to compare:

            i7-970    (6 core, 3 channel, 25.6GB/s)

            i7-920    (4 core, 3 channel, 25.6GB/s)

            i7-2600K (4 core, 2 channel, 21GB/s)

            i7-3930K (6 core, 4 channel, 21GB/s)

             

            Note what I show in parenthesis. The older tiple channel cpu's have faster max data rate, and 2 vs 4 channel memory shows no difference.

            • 3. Re: Quad channel cpu's lower bandwidth then triple channel?!?!
              Adolfo_Intel

              You need to keep in mind that the older processors i7-920 and i7-970 do not have embedded graphics controller, so they do not need to share the bandwidth  with the video controller, however in the case of the i7-2600K and i7-3930K, they do have graphics controller embedded, so they need to chare the bandwidth with the graphics controller.

              • 4. Re: Quad channel cpu's lower bandwidth then triple channel?!?!
                adilhussain21

                by ''embedded graphics controller'' are you refering to the Graphics Sepcification that the i7-2600K has listed at : http://ark.intel.com/compare/52214

                but i dont see any graphics specification for the i7-3930K, has it been degraded graphics wise to keep the i7-2600K on the market-shelevs?

                this will help you to compare :  http://ark.intel.com/compare/52214,63697

                 

                I am a hardcore gamer so the i7-2600K suits my needs, but i do quite i lot of multitasking like running 4 virtual machinces (Oracle VM VirtualBox, OS as WinXP all 4) while gaming, so i thought of getting a stronger cpu the 3930K but then i noticed that the 3930k has no graphics specifications.

                 

                What CPU will be the best for me, provide i dont spend more than $700 since i need the other $700 for a MOBO, Memory Chip, Aftermarket Water Cooler.

                Will the 3930K be able to handle the load?

                • 5. Re: Quad channel cpu's lower bandwidth then triple channel?!?!
                  kwhubby

                  Adil, your comparison link looks like it disproves adolpho's response. Without the graphics controller, and double the memory controllers- why does the 3930K claim the same memory bandwidth as the 2600K?. Something isn't adding up right... 2 x DDR3-1066/1333  = 4 x DDR3-1600?  Faster ram and double the bus width shouldn't perform the same.  If these are indeed correct and not a typo or marketing ploy (maybe 4 is really 2), I would have to guess the memory bandwidth is being limited by some internal bus between the ddr3 memory controllers and the MMU/cache controllers. This seems like a design flaw to me, short on die busses should be able to exceed the bandwidth of external traces- wasn't this the point of having integrated memory controllers on cpu's rather than a north bridge.

                   

                  This leads me to another question: would running the same ram configuration on both chips, let's say 2xDDR3-1333  result in the same memory performance, or would the 3930K have lower bandwidth? Retest using 4xDDR3-1333 and I ask the same question.

                  • 6. Re: Quad channel cpu's lower bandwidth then triple channel?!?!
                    adilhussain21

                    I agree with you kwhubby. Im quite sure this isn't a typo but a marketing ploy and a design flaw, a combination of both. Concluding that memory bandwidth for  the quad channel processors is lower than the triple channel processors this way the triple channel processors remain on the market shelves for a longer time and dont get replaced by the 2nd generation core i7s and wether the memory chips are quad channel or dual channel they are the same thing.