PCI Express 3.0: On Motherboards By This Time Next Year?

Analysis: Where We’ll Use PCI Express 3.0


AMD is already integrating support for SATA 6Gb/s into its 8-series chipsets, and third-party motherboard vendors are adding USB 3.0 controllers. Intel is lagging behind in this area, with no chipset support yet for either USB 3.0 or SATA 6Gb/s (Ed.: Note that pre-production P67-based motherboards we've seen here in the lab do incorporate SATA 6 Gb/s support, but lack USB 3.0). However, as we’ve often seen in the AMD versus Intel saga, innovation at AMD usually inspires Intel. Given the data rates for both next-generation storage and peripheral interconnects, it's clearly not necessary to drop either technology onto PCI Express 3.0. Rather, a single lane of second-generation PCI Express is ample for both USB 3.0 (at 5 Gb/s) and SATA 6 Gb/s (which no storage device can even come close to saturating).

Of course, when it comes to storage, the interaction between drives and controllers is only part of the equation. Consider that dropping multiple SSDs on a SATA 6 Gb/s chipset and creating a RAID 0 array does actually have the potential to saturate the single lane of second-gen PCI Express that most motherboard vendors are using for their implementations. Deciding whether USB 3.0 and SATA 6 Gb/s can truly utilize PCI Express 3.0 support requires a closer look at the math.

As mentioned, USB 3.0 runs at 5 Gb/s. But as with PCI Express 2.1, USB 3.0 employs 8b/10b encoding, which lowers the actual peak speed to 4 Gb/s. Divide bits by eight to convert to bytes, and you get a peak throughput of 500 MB/s, which is the exact same speed as a modern PCI Express 2.1 lane. SATA 6Gb/s runs at 6 Gb/s of course, but its own 8b/10b encoding scheme drops the peak rate from a theoretical 6 Gb/s to an actual speed of 4.8 Gb/s. Again, convert that to bytes and you get 600 MB/s, or 20% more than the peak speed of a PCI Express 2.0 lane.

The problem here is that even the fastest SSDs cannot fully saturate a SATA 3 Gb/s connection. Nothing comes close to saturating a USB 3.0 connection, and the same holds true for the latest iteration of SATA 6Gb/s. At least as far as we're concerned today, PCI Express 3.0 isn't really a necessity for driving the biggest buzzwords in the platform space. Hopefully, as Intel shifts into its third generation of NAND flash manufacturing, however, speeds increase and we start to see devices capable of pushing beyond what a 3 Gb/s SATA port could have sustained in the past.

  • cmcghee358
    Good article with some nice teases. Seems us regular users of high end machines won't see a worth until 2012. Just in time for my next build!
  • tony singh
    What the..... pcie3 already devoloped & most games graphics are still of geforce 7 level thnk u consoles..
  • darthvidor
    just got pci-e 2.0 last 2008 with my x58 ... time's flying
  • iqvl
    Good news to peoples like me who haven't spent any money on PCIE 2.0 DX11 card due to nVidia's delay in shipping GTX460.

    Can't wait to see PCIE 3.0, native USB3/SATA3, DDR4, quad channel and faster&cheaper SSD next year.

    In addition, I hate unreasonably priced buggy HDMI and would also like to see the Ethernet cable(cheap, fast and exceptional) based monitors as soon as possible.

    One more tech that I can't wait to see: http://www.tomshardware.com/news/silicon-photonics-laser-light-beams,10961.html

    WOW, so much new techs to be expected next year!
  • ytoledano
    Processor speed *is* increasing exponentially! Even a 5% year-on-year increase is exponential.
  • Casper42
    I havent read this entire article but on a related note I was told that within the Sandy Bridge family, at least on the server side, the higher end products will get PCIe 3.0.

    And if you think the Core i3/5/7 desktop naming is confusing now, wait till Intel starts releasing all their Sandy Bridge Server chips. Its going to be even worse I think.

    And while we're talking about futures, 32GB DIMMs will be out for the server market most likely before the end of this year. If 3D Stacking and Load Reducing DIMMs remain on track, we could see 128GB on a single DIMM around 2013, which is when DDR4 is slated to come out as well.
  • JonnyDough
    After an unfortunate series of untimely delays, the folks behind PCI Express 3.0 believe they've worked out the kinks that have kept next-generation connectivity from achieving backwards compatibility with PCIe 2.0. We take a look at the tech to come.

    It's nice to see the backwards compatibility and cost be key factors in the decision making. Especially considering that devices won't be able to saturate it for many years to come.
  • rohitbaran
    Nothing in the world of graphics is getting smaller. Displays are getting larger, high definition is replacing standard definition, the textures used in games are becoming even more detailed and intricate.
    Even the graphics cards are getting bigger! :lol:
  • iqvl
    rohitbaranEven the graphics cards are getting bigger!I believe that he meant gfx size per performance. :)
  • Tamz_msc
    We do not feel that the need exists today for the latest and greatest graphics cards to sport 16-lane PCI Express 3.0 interfaces.
    Glad you said today, since when Crysis 3 comes along its all back to the drawing board, again.