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Re: Confused with GA-P55A-UD4P using USB 3 and SATA 6Gb

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      01-26-2010, 01:14 AM
Scott wrote:
> There are several comments:
> that state you can't use USB 3.0 and SATA 6Gb/s with crossfire or SLI
> but after looking at the block diagram in the manual, USB 3 and SATA 6Gb
> both hang off the P55 while the PCI x16 and x8 slots both hang off the CPU.
> Scott

You can. If you run two graphics cards, the USB3 and SATA3 run in non-turbo mode.
If you had things connected to them, they'd still work. Just not as fast as when
turbo mode is enabled.

It would be nice, if some review site got to the bottom of that, but so
far, I haven't seen any mention of what thing they did on the boards for that
to happen. I think it might be a clock distribution issue (the P55 creates
clocks for the system), but I can't be sure of that. I'd need to see a
real detailed photo of the motherboard (not a Newegg quality photo), to
make more sense of it. Preferably, a photo where all the heatsinks have
been removed as well. A trend now on these boards, is to put down two
heatsinks, one for the P55, and the other one "hides stuff" like the
logic chips used to switch the lanes running to the PEG slots. There
might be something interesting hiding under there.

While it is nice of Gigabyte to put a block diagram in the manual, sometimes
the way it is drawn, isn't quite right. In the case of the GA-P55A-UD4P,
it is possible the "switch" isn't connected as shown. It should be
similar to what is done on P45 boards. That logic should be the equivalent
of the paddle cards that the old SLI motherboards used to have on them.
In the diagram here, you run either x16/x0 or x8/x8. The processor itself
only supports x8/x8 when used with two slots. Adding the external
multiplexing/demultiplexing chip(s) makes it possible to do x16/x0 or x8/x8
electronically, without a paddle card scheme. You could replace the Mux
with a paddle card, to steer the lanes to the upper or the lower slot.

x8 x8
PEG#1 ---------------- Processor
-----+ has the
x8 | x8 video card
Mux-------- interfaces
PEG#2 -----+

In the P45 motherboards, they leave the four chips out in the open.
In the photo here, the four chips to the left of the primary PEG slot,
support the feature in the above diagram ("Mux"). On P55, they seem to
like to hide that solution underneath a heatsink.$S640W$

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