9 Replies Latest reply on Sep 11, 2017 10:46 AM by amdmatt

    Bandwidth - PCI & CPU

    boston_hike

      I give up! Sorry for the rant but her it goes: I've searched YouTube and some of Google with no luck. I'm probably asking the question incorrectly, though. So this is my first go round building a PC and I was told I need to be weary of PCI lanes...or bandwidth...or threads...idk, these terms seem to be interchangeable at this point. My current understanding (probable misconception) is that the CPU has a set number of PCI lanes. And the same can be said for the motherboard. And by use of wonderful mathematicals, we can combine the two numbers to reach our max number of threads.

       

      So lets take this for example: I have with me a R7 1700x and an Asus Strix X370-F Mobo. The R7 has 16 threads. I don't even know how to find the Mobo chipset lane count...Anyways, my friend made it sound like if I chose a lesser Ryzen chip and a b350 mobo, I wouldn't be able to optimally run any SLI or Crossfire due to too few threads. He made it sound like the lanes of the CPU is combined with the mobo lanes and I can only get a set amount of devices before I run out of threads. But then how are so many people just throwing 3 GTX 1080ti's onto little CPU's? Ugh, I hate this. The moment I think I have a grasp on it all, I have to worry about lanes...

       

      I am not really looking for a dictionary definition with this. Try explaining it as if you were explaining it to a noob, possibly through analogies. Maybe provide a little table or method to find how many threads I have and how different devices affects them (m.2, gpu's, sound cards, etc.).

       

      This is what I'm working with:

      -Ryzen 7 1700x

      -NZXT Kraken X62 Cooler

      -Asus Strix X370-F Mobo

      -G.Skill DDR4-3200MHz RAM

      -Corsair 120GB M.2 SSD

      -WD 1TB HDD

      -Corsair HX750i PSU

      ..As for GPU, I currently have Asus Strix GTX 1050 ti (got it dirt cheap and only have a 1080p TV.. QHD, 144hz monitor to come). Future plan is to run 2 GPU's of GTX 1080, RX Vega, or equivalent...most likely Vega.

      Thanks!

        • Re: Bandwidth - PCI & CPU
          black_zion

          Threads - The number of tasks which the OS's scheduler can schedule. Think of them as workers. A program can request more workers in order to complete a task faster

           

          PCI Express Lanes - The number of electrical PCI Express connections between two components.

           

          Bandwidth - The amount of data which can flow between two components.

           

          The CPU has a small number of PCI Express lanes which are used to interconnect through the motherboard, especially between the CPU and external chipset, and the rest are divided up however the manufacturer decides, be it SATA ports, an M.2 slot, external PCI Express, or a combination of the three. The chipset itself has a number of PCI Express lanes, and the X370 is the only one with enough to power a PCI Express 3.0 x8/x8 setup, which is plenty for dual graphics cards.

          1 of 1 people found this helpful
          • Re: Bandwidth - PCI & CPU
            enormouschunks

            I always explained it like this.

             

            Think of it as destinations.

            PCI-E, SATA, M.2, CPU

             

            The PCI lanes are exactly that, lanes. They get you from destination A to destination B.

             

            Threads relate to CPU. How many different work centers are at that destination.

             

            Bandwidth is the size of the BUS. How many people can the bus fit.

              • Re: Bandwidth - PCI & CPU
                boston_hike

                Alright. I feel I have a grasp on what lanes are and how they work. However, would a single gpu take up all 16 lanes of the R7? And then the chipset handles the sata, m.2 and so forth?

                  • Re: Bandwidth - PCI & CPU
                    black_zion

                    The motherboard manufacturer determines how the PCIe lanes are divvied up. Take the ASUS Strix X370-F for example:

                     

                     

                    The board has 3 PCIe x16 physical slots, and 3 PCIe x1 physical slots. With a Ryzen processor, one of those PCIe x16 slots will run at full x16 if one is populated, or two at x8 if both are populated, the third will always run at x4, or less if two of the PCIe x1 slots are populated. PCIe is not dynamically allocated, so you can't have something like x10/x6, so if you just use one graphics card, the second slot is essentially unpowered with the GPU getting all 16 lanes.

                     

                    On that board, the M.2 slot does not share bandwidth with SATA slot, so it will run with its 4 dedicated lanes.

                    2 of 2 people found this helpful
                • Re: Bandwidth - PCI & CPU
                  enormouschunks

                  This may be a little off.

                  If you are gaming, I would get a single GPU.


                  Also a bigger M.2 SSD will hugely benefit you in the future. 120GB will fill up super quickly.

                   

                   

                   

                  boston_hike wrote:

                   

                   

                  This is what I'm working with:

                  -Ryzen 7 1700x

                  -NZXT Kraken X62 Cooler

                  -Asus Strix X370-F Mobo

                  -G.Skill DDR4-3200MHz RAM

                  -Corsair 120GB M.2 SSD

                  -WD 1TB HDD

                  -Corsair HX750i PSU

                  ..As for GPU, I currently have Asus Strix GTX 1050 ti (got it dirt cheap and only have a 1080p TV.. QHD, 144hz monitor to come). Future plan is to run 2 GPU's of GTX 1080, RX Vega, or equivalent...most likely Vega.

                  Thanks!

                  • Re: Bandwidth - PCI & CPU
                    amdmatt

                    We have updated the title of this discussion with relevant details to better describe your issue.