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Gigabyte P55A-UD3 and USB/SATA 3

10474 Views 8 Replies 6 Participants Last post by  andynolife, 
M
A little confused....I'm looking at getting a Gigabyte P55A-UD3. I understand that in order to use USB 3.0 and SATA 6Gb/s, you cannot use the 2nd PCIe slot, otherwise USB/SATA get downgraded to normal speeds. Question is, what about the 1st PCIe slot? Does it remain at 16x with USB 3.0 and SATA 6Gb/s enabled, or does it go down to 8x?

thanks,
Michael
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T
Huh, you can only use 1 PCI-E slot if you want SATA-III?

That's one big, epic, massive FAIL. Does not want!

Also the difference between 8x and 16x is tiny unless you are using a monster of a card (HD 5970)
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Tomalak
1st PCIEx16 slot will get limited to x8. The second PCIEx16 slot, which is limited to x4 by default and connected to the chipset, will be unaffected.

Basically, if you enable USB/SATA3, first PCIEx16 slot gets down to x8, second PCIEx16 slot (if you have it, UD3 doesn't) gets disabled, and third PCIEx16 slot (if you have it, its the one limited to x4 and connected to the chipset) remains unaffected.

EDIT: To clarify - PCIEx16 slots which are connected to the chipset, and limited to x4 (for example, on UD3 or UD5) are not affected by enabling USB/SATA3.

This means that, if you're planning on single GPU on a P55A board (with USB/SATA3 enabled), UD3R is a better option then UD4, for example.
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Starbuck5000
Quote:

Originally Posted by mraviator View Post
A little confused....I'm looking at getting a Gigabyte P55A-UD3. I understand that in order to use USB 3.0 and SATA 6Gb/s, you cannot use the 2nd PCIe slot, otherwise USB/SATA get downgraded to normal speeds. Question is, what about the 1st PCIe slot? Does it remain at 16x with USB 3.0 and SATA 6Gb/s enabled, or does it go down to 8x?

thanks,
Michael
From some Gigabyte slides on their power of 3 stuff:

Quote:
By selecting Turbo S-ATA 3 mode, Marvell SE9128 controller will be running at PCI-E x1 Gen 2 speed, then dual PCI-E graphics mode is disabled and the 1st PCI-E x16 slot will run at x8 bandwidth
So when running at Sata 6Gb/s the top slot will only run at pci-e 2.0 x8. Its not clear whether or not you can use the second pcie slot for pcie cards other than graphics card, but the fact that the top slot is downgraded to x8 makes me think that the second slot is disabled all together.
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Tomalak
Quote:

Originally Posted by Starbuck5000 View Post
So when running at Sata 6Gb/s the top slot will only run at pci-e 2.0 x8. Its not clear whether or not you can use the second pcie slot for pcie cards other than graphics card, but the fact that the top slot is downgraded to x8 makes me think that the second slot is disabled all together.
There are three types of PCIEx16 slots on P55:

1. 1st PCIEx16 slot, capable of running at x16 or x8, if the second PCIEx16 slot is in use.

2. Second PCIEx16 slot, which shares lanes with the first one. If both are in use, they go down to x8/x8.

3. Additional PCIEx16 slot, connected to the chipset, and limited to x4. This slot doesn't share lanes with the others, and is NOT affected by USB3/SATA3 slot being enabled.

Examples:
UD4 has 1 and 2,
UD3 has 1 and 3,
UD5 has 1,2 and 3.
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M
Thanks for the responses everybody. I am planning on using a single GPU (ATI HD 5750 or 5770) and was mostly concerned how 8x might affect its speed. I need to sort through the replies and see how this might affect my choices. The other MB I am looking at is MSI's GD65.
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Tomalak
Quote:

Originally Posted by mraviator View Post
Thanks for the responses everybody. I am planning on using a single GPU (ATI HD 5750 or 5770) and was mostly concerned how 8x might affect its speed. I need to sort through the replies and see how this might affect my choices. The other MB I am looking at is MSI's GD65.
With 5750 or 5770 you will be perfectly fine at x8.
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W
I'm kicking myself for going with the UD3 as I have 2 HD5770's running..... time to sell and go with the UD7 and live in bliss
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A
The UD3 has 2 PCIe x16 slots. The first one is linking to the CPU directly and the second one is from the P55 chipset which is a gen1 x4

The UD4 and up with the x8/x8 lanes are dividing the x16 lane from CPU into 2 PCIe lanes.

The fact that the P55 chipset regardless which brands you are running simply does not have enough bandwidth to support full speed SATA3. Thus, gigabyte's solution is using one of the x8 PCIe lane from the CPU to get the full speed of SATA3 or USB3. However, the gigabye boards have the ability to choose in the BIOS to set it to full speed - via PCIe 8x lane from the CPU or running at half the speed via the P55 chipset which is still 5+ times faster then USB2.0.
The second PCIe x16 slot on the UD3/UD3P is linked to the P55 chipset, running at x4 gen1. However, it will be running at x1 speed if any of the PCIe x1 slots are being used. This also applied to any boards using the PCIe lanes from the P55 chipset links to the PCIe x16 slot.
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