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PCI Express 2.0 Details

PCI Express 2.0 Graphics Cards Tested
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pci express 2.0

PCI Express 1.1 and 2.0 slots are the same mechanically. The upper one has all the 164 pins required for a x16 PCI Express connection, while the lower connector is utilized for PCI Express x1 and has 36 pins.

While PCI was a 32 bit or 64 bit parallel bus that had to be shared by all client devices, PCI Express is a serial interface based on point-to-point links. This means that bandwidth is exclusively available for each device, and multiple connections are handled via PCI Express switching, similar to how Ethernet switching works . Despite the tremendous differences when compared to parallel PCI, PCI Express is software compatible with PCI, meaning that any operating system that supports PCI will also work with PCI Express.

PCI Express utilizes two connection pairs that operate at a 2.5 GHz base clock speed. Using an 8/10 bit encoding method — meaning that 10 bits gross are transferred to reach 8 bit net bandwidth — a single PCI Express connection reaches 250 MB/s gross bandwidth. As there are two connection pairs, you’ll get this bandwidth in both the upstream and downstream directions. PCI Express can deliver much higher bandwidth by combining multiple connections, which are referred to as lanes. Thus, x8 PCI Express offers eight times the throughput (4 GB/s) of a single lane connection, while x16 PCI Express, which has been the interface for all sorts of graphics cards, can access a total bandwidth of 8 GB/s.

PCI Express 2.0 doubles the transmission speed to 5.0 GHz, and hence doubles the throughput to 16 GB/s peak bandwidth of x16 PCI Express. We’ll find out in this article whether or not this is necessary for current graphics cards; but it is certainly the case that the new standard offers more flexibility to hardware manufacturers. Since four PCI Express 2.0 connections deliver the same bandwidth as eight PCI Express 1.1 links, it’s possible to create interconnects to either double the throughput, or to optimize power requirements by switching from 1.1 to 2.0 mode at half the number of lanes. In addition, PCI Express 2.0 still supports 1.1 speeds, which allows for further energy savings due to the links’ speed reduction from 5.0 to 2.5 GHz when throughput isn’t required. If properly implemented, PCI Express 2.0 automatically negotiates link width (from a few to 16 links) and link speed (2.5 or 5 GT/s). This also means that PCI Express 2.0 graphics cards are compatible with PCIe 1.1 motherboards: they will simply stay at the 2.5 GB/s link speed.

Another improvement between PCI Express 1.1 and 2.0 is the maximum power that can be provided for PCI Express graphics cards (PEG). While this used to be 75 W plus 75 W auxiliary power for PCI Express 1.1, PCIe 2.0 now supports a maximum of up to 300 W when fully implemented on a motherboard. Graphics board designers still have to work with auxiliary power connectors, though — PCI Express 2.0 compliant power supply units now require an 8-pin auxiliary power port in addition to the 6-pin connector, which has been around since the introduction of PCIe in 2004.

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  • 1 Hide
    romulus47plus1 , April 22, 2008 6:48 AM
    Cool review.
  • 0 Hide
    gailim , April 22, 2008 6:56 AM
    "only the latest GeForce 9 graphics cards are PCIe 2.0 compliant."

    thats incorrect. the G92 based 8 series cards are also PCIe 2.0
  • 0 Hide
    leo2kp , April 22, 2008 7:31 AM
    *sigh* looks like it's a new mobo for me. it was a good run GA-965P-DQ6!
  • 0 Hide
    hughyhunter , April 22, 2008 7:43 AM
    What's up TOM's? PCIe 2.0 compliant? Only 9 series. Like mentioned... G92 is PCIe 2.0!
  • 2 Hide
    LuxZg , April 22, 2008 7:59 AM
    Just prooves two things - first that even PCIe 1.1 x8 is good for most cards & applications (same bandwith as x4 PCIe 2.0) as you lose 0-4% in all but heaviest apps like Flight Simulator and Crysis with AA/AF enabled; and second, that lower end graphics card can be used on PCIe 2.0 x4 slots without any problems, and for entry level you can make PCIe x1 cards just like the PCI ones that are sometimes used for smaller servers and such..

    So I just wonder, will they ever start making x1 and x4 cards.. And I mean with _physical_ x4 or x1 slots, as you really can't plug x16 card in x1 slot unless you use a saw :D 
    It would also make multi-monitor setups much cheaper than using MBOs with 4x PCIe x16 slots and I bet x1 PCIe graphics cards would be much cheaper as they'd have less complicated and smaller PCB as well.
  • 0 Hide
    oushi , April 22, 2008 8:12 AM
    Nothing ground-breaking, but interesting read nonetheless...
  • -1 Hide
    LuxZg , April 22, 2008 8:14 AM
    Oops, my bad, they already exist :S Though I've never seen any in pricelists in my country :( 
    And these x1 cards that I've found (X1550 & 8400GS) aren't really cheap for 100+$, as x16 cards are less than half the price. Kinda kills the main reason of NOT SPENDING too much money.. as for extra 50-60-70$ you can get a better MBO in the first place :rolleye: :p 
  • -1 Hide
    hayder_master , April 22, 2008 8:23 AM
    i think compare also be with hd 3870 x2
  • 0 Hide
    hayder_master , April 22, 2008 8:34 AM
    i think if thay use ati 3870 x2 it will be give more results than geforce 9800 x2
  • 0 Hide
    Gazz , April 22, 2008 10:13 AM
    I have an MSI k9a2 platinum now I can either have 2 cards running at 16x each or 4 cards running at 8x
    So what would be better 2 x ati 3870x2 or 4 x 3870
    and would the 2x ati 3870x2 run at 8x or 16x
    because if they run at 8x then i might be better off with 4 x 3870 runing at 8xor would the two 2 x 3870x2 run faster then 4x3870
    at the moment i have 2 1900xtx
  • 0 Hide
    homerdog , April 22, 2008 12:26 PM
    Quote:
    While ATI has been quick with deploying PCIe 2.0 to its Radeon HD 3000 family, only the latest GeForce 9 graphics cards are PCIe 2.0 compliant.

    I think not.
  • 0 Hide
    San Pedro , April 22, 2008 1:32 PM
    It sounded like the article was recommending people move from their pci-e 1 motherboards to pci-e 2. The 1 speeds were 99% as fast most times. Flight simulator was the only game that saw a significant improvement going to new interface. I don't think that small difference in performance warrants the time and effort if you already have pci-e 1.0 or 1.1 motherboard.
  • 0 Hide
    homerdog , April 22, 2008 3:29 PM
    Quote:
    It sounded like the article was recommending people move from their pci-e 1 motherboards to pci-e 2. The 1 speeds were 99% as fast most times. Flight simulator was the only game that saw a significant improvement going to new interface. I don't think that small difference in performance warrants the time and effort if you already have pci-e 1.0 or 1.1 motherboard.

    The gains from PCIe 2.0 are minimal right now, but they will likely be more pronounced as newer cards are released, especially for multi-GPU configurations which seem to be all the rage. At this point I am finding it more and more difficult to recommend PCIe 1.x boards with the P4X chipsets on the horizon and the 750i already out.
  • 0 Hide
    MrCommunistGen , April 22, 2008 4:01 PM
    Epic fail... not so much the article itself but some of the things in it. Actually I liked the overall article for the insight it provided because it reinforced what I've been telling people for months. I guess the most glaring of the problems is that I get a 404 error when I try to view the conclusion page. (err... I just went back to try to read something and am getting a 404 for the whole article). Not that I can't draw my own conclusions from what I read, I just like to see someone else say it... and of course I like being able to read the whole article.
    That aside, someone goofed the batchwork on the graphs. The AMD graphs have Nvidia in the key but the Nvidia graphs are separate, and about half the graphs are "normal" .png files and the others are poorly compressed .jpg. Not that this is a big deal, but it only takes a minute to fix any of these quibbles and it takes away from the polish of the article... otherwise it seems to fit with the "Tom's is on an upswing" comment I think I read about yesterday's article about the VelociRaptor.

    -mcg
  • 0 Hide
    MrCommunistGen , April 22, 2008 4:08 PM
    OK... the 404 error disappeared. I read the conclusion page, and I don't like how they ignored the fact that lowered speeds sometimes outperformed higher speeds. In a few cases 8x and 4x slightly outperformed 16x. I wish they had explained that this was most likely due to "margin of error and signified no change" or something like that because I can completely see a noob quoting the article and asking if Crysis will perform better at 8x than 16x because several of the article benches showed this.

    -mcg

    Edit: HA!! I didn't realize that the "talkback" under the articles was actually posting on the forum or I would have just edited my first message.
  • 0 Hide
    DXRick , April 22, 2008 5:50 PM
    I was hoping to see PCIe x16 2.0 (X38 chipset) versus PCIe x16 (P35).
  • 0 Hide
    bgd73 , April 22, 2008 6:30 PM
    excellent info. To go back even farther to a pci-e convertor sitting on top of an agp fitted card....What we see as written is just that in this article. Written.Just like CPU's and labels of "core duo". There are many items out there, and have been out there for years, with no name- doing what is now written. This is all for the sake of knowing it has a name. No panics for upgrades, if you do...there is not all that much surprise.
  • 0 Hide
    xTalent , April 22, 2008 8:08 PM
    The last page says "9900 GX2" :D 
  • 0 Hide
    sceen311 , April 22, 2008 9:55 PM
    So SLI PCIE 2.0 vs PCIE 1.1 that's something I would have like to have seen.
  • 1 Hide
    tipoo , April 22, 2008 10:18 PM
    last page, it should say 9800GX2, not 9900 :) 
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