Re: new bottleneck section in wiki

Doug Ledford <dledford@xxxxxxxxxx> · Thu, 03 Jul 2008 01:10:48 -0400

On Wed, 2008-07-02 at 14:03 -0500, Matt Garman wrote:
> 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 32bit/33MHz card only slows down the particular bus it's plugged into.
A lot of the server class machines that have had PCI-X in the past made
a specific point of using multiple PCI busses for the slots so that
plugging in that 32bit/33MHz card wouldn't effect the PCI-X card next to
it because they were on physically distinct busses.

> 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?

Again, different physical busses.

> 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
> 
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Doug Ledford <dledford@xxxxxxxxxx>
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