On Wed, Jul 02, 2008 at 12:04:11PM -0500, David Lethe wrote: > The PCI (and PCI-X) bus is shared bandwidth, and operates at > lowest common denominator. Put a 33Mhz card in the PCI bus, and > not only does everything operate at 33Mhz, but all of the cards > compete. Grossly simplified, if you have a 133Mhz card and a > 33Mhz card in the same PCI bus, then that card will operate at > 16Mhz. Your motherboard's embedded Ethernet chip and disk > controllers are "on" the PCI bus, so even if you have a single PCI > controller card, and a multiple-bus motherboard, then it does make > a difference what slot you put the controller in. Is that true for all PCI-X implementations? What's the point, then, of having PCI-X (64 bit/66 MHz or greater) if you have even one PCI card (32 bit/33 MHz)? A lot of "server" motherboards offer PCI-X and some simple graphics chip. If you read the motherboard specs, that simple graphics is usually attached to the PCI bus [1]. So what's the point of having PCI-X slots if everything is automatically downgraded to PCI speeds due to the embedded graphics? I read some of the high-level info on the Intel 6702 PHX PCI-X hub [2]. If I understand correctly, that controller is actually attached to the PCI express bus. So to me, it seems possible that PCI and PCI-X could be independant, and that PCI-X will compete with PCI-E for bandwidth. [1] The ASUS M2N-LR has PCI-X (via the Intel 6702PHX) and an embedded ATI ES1000 video card. The ES1000's specs say it has a PCI bus interface. ES1000: http://ati.amd.com/products/server/es1000/index.html [2] http://www.intel.com/design/chipsets/datashts/303633.htm -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
