Please report all spam threads, posts and suspicious members. We receive spam notifications and will take immediate action!
Results 1 to 5 of 5

Thread: 16x PCI-e vs 8x PCI-e in CrossFire/SLI (The Answer..)




  1. #1
    Join Date
    Apr 2009
    Posts
    32

    Default 16x PCI-e vs 8x PCI-e in CrossFire/SLI (The Answer..)

    It seems many threads all over the internet has/had/have asked this same question all over.

    was tweaktown's review really truthful ? sadly.. it wasn't.

    Difference between 16x PCI-e vs 8x PCI-e in CrossFire/SLI ?

    Answer:

    Here is why.

    PCI-e 2.0 16X = 8GB/s total bandwidth
    PCI-e 2.0 8X = 4GB/s total bandwidth

    ATI:

    HD 3870 = 1125mhz (dual piped - 2.2 GB/s data rate) = 2.2 GB/s total data rate
    HD 4650 = 500mhz (dual piped - 1 GB/s data rate) = 1 GB/s total data rate
    HD 4670 = 1000mhz (single piped - 2 GB/s data rate) = 2 GB/s total data rate
    HD 4770 = 800mhz (quad piped - 3.6 GB/s data rate) = 3.6 GB/s total data rate
    HD 4830 = 900mhz = (dual piped - 1.9 GB/s data rate) = 1.9 GB/s total data rate
    HD 4850 = 993mhz (dual piped - 1.9 GB/s data rate) = 1.9 GB/s total data rate
    HD 4850 X2 = 993mhz (dual piped - 1.9 GB/s data rate)(times 2) = 3.8 GB/s total data rate
    HD 4870 = 900mhz (quad piped - 3.6 GB/s data rate) = 3.6 GB/s total data rate
    HD 4890 = 975mhz (quad piped - 3.9 GB/s data rate) = 3.9 GB/s total data rate
    HD 4870 X2 = 900mhz (quad piped - 3.6 GB/s data rate)(times 2) = 7.2 GB/s total data rate

    So as you can see, the 4870 X2 will be hurt in an 8X condition and why the 3870, 4650, 4670, 4770, 4830, 4850, 4870, 4890, and 4850 X2 will not be hurt in performance at all.

    Nvidia:

    8800 Ultra = 1080mhz (dual piped - 2.1 GB/s data rate) = 2.1 GB/s data rate
    9600 GT = 900mhz (dual piped - 1.8 GB/s data rate) = 1.8 GB/s total data rate
    9800 GTX = 1100mhz (dual piped - 2.2 GB/s data rate) = 2.2 GB/s total data rate
    GTS 250 = 1100mhz (dual piped - 2.2 GB/s data rate) = 2.2 GB/s total data rate
    GTX 260 216 = 999mhz (dual piped - 1.9 GB/s data rate) = 1.9 GB/s total data rate
    GTX 275 = 1134mhz (dual piped - 2.2 GB/s data rate) = 2.2 GB/s total data rate
    GTX 280 = 1053mhz (dual piped - 2.1 GB/s data rate) = 2.1 GB/s data rate
    GTX 285 = 1242mhz (dual piped - 2.4 GB/s data rate) = 2.4 GB/s data rate
    GTX 295 = 999mhz (dual piped - 1.9 GB/s data rate)(times 2) = 3.8 GB/s total data rate
    GTX 285X2 = 1242mhz (dual piped - 2.4 GB/s data rate)(times 2) = 4.8 GB/s data rate

    So as you can see, the GTX285 X2 will be hurt in an 8X condition and why the 8800, 9600, 9800, 250, 260, 280, 275, 285 & 295 will not be hurt in performance at all.

    Check this pic:


    This should be a clear message to anyone wanting to do multi-gpu setup's, people with PCI-e 2.0 @ 16x-16x-8x or 16x-8x-8x or even 8x-8x-8x bandwidth should have no bottle neck for any single gpu cards in the market, aside from the double gpu cards like 4870x2, and incoming GTX285x2.

    a quick example:

    Which is better performance in fps/gaming, 16x-8x-8x w/ PCI-e 2.0 motherboard vs 16x-16x-16x w/ PCI-e 2.0 motherboard vs 8x-8x-8x w/ PCI-e 2.0 motherboard:
    Code:
    1x 4870 1GB @ 16x slot
    1x 4870 1GB @ 8x slot
    1x 4870 1GB @ 8x slot
    vs
    1x 4870 1GB @ 16x slot
    1x 4870 1GB @ 16x slot
    1x 4870 1GB @ 16x slot
    vs
    1x 4870 1GB @ 8x slot
    1x 4870 1GB @ 8x slot
    1x 4870 1GB @ 8x slot
    Winner:
    Draw, no difference in fps. Although some 16x-16x-16x boards with n200 chipset's has fps drops in games which is reviewed many times but no drops in benchmarking (3dmarks,vantage). If your board is PCI-e 1.0 then that would be a huge difference :)

  2. #2
    Join Date
    Nov 2008
    Location
    Vancouver, Canada
    Posts
    167

    Default Re: 16x PCI-e vs 8x PCI-e in CrossFire/SLI (The Answer..)

    Good info Zero.

    Nice and easy to see all the numbers like this :).

    Just noticing 4870X2=7.2GB/s, so 4890X2 would be 7.8GB/s .?.
    With PCI-e 2 x16 @ 8GB/s, we're gonna need more bandwidth (PCI-e 3) very soon >.<.

    GTX 285X2 o.0!
    Only thing I found was the Asus Mars. Is that what you meant?
    Last edited by C3D76; 07-31-2009 at 03:21 AM.
    Windows 7 Pro 64 | OCZ Vertex 120 | Cosmos S
    Gigabyte P67A-UD5-B3 (F6) | Enermax Revolution85+ 1050w
    i7 2600k | 2x4 GB Corsair Vengeance 1866 | EVGA GTX570 SC
    Apogee XT | Magicool 360 Radiator | MCP35x Pump + v.2 Res

  3. #3
    Join Date
    Apr 2009
    Posts
    32

    Default Re: 16x PCI-e vs 8x PCI-e in CrossFire/SLI (The Answer..)

    Yep, but there is no 4890x2 in the market...

    and yes gtx 285x2 = Asus Mars

  4. #4
    Join Date
    Nov 2007
    Location
    Australia
    Posts
    286

    Default Re: 16x PCI-e vs 8x PCI-e in CrossFire/SLI (The Answer..)

    theres an article over at tomshardware comparing PCI-e x16/8/4/2/1 crossfire speeds and single card speeds.

    go check it out
    Asrock P55-Extreme
    Core I5 @ 3.2GHZ
    2x2GB G.skill Ripjaws DDR3 1600
    ASUS HD5850
    1TB Samsung SATA II
    Corsair TX650W PSU

  5. #5
    Join Date
    Aug 2009
    Posts
    1

    Default Re: 16x PCI-e vs 8x PCI-e in CrossFire/SLI (The Answer..)

    Quote Originally Posted by zerosaku View Post
    It seems many threads all over the internet has/had/have asked this same question all over.

    was tweaktown's review really truthful ? sadly.. it wasn't.
    EXCEPT that your numbers make no sense whatsoever.

    You have listed the memory frequency of many video cards and somehow linked the bandwidth-per-pin, that is, the bandwidth per 1bit of memory bus of the cards' VRAM to PCIe link bandwidth and made deductions on bottlenecking based on this invalid comparison.

    FACT IS, the video card -specific bandwidth numbers listed in OP have absolutely nothing to do with PCIe bandwidth. There's no sense at all to compare them and no conclusions whatsoever can be made based on them.

    =)
    Last edited by largon; 08-31-2009 at 08:40 PM.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •