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Graphics card in 2nd slot.

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June 11, 2009 2:23:45 AM

Hey All,
Would it be possible to put my graphics card in the secondary PCIe slot in my ASUS P6T deluxe v2?
I need both PCI slots and my 8800gtx takes up too much space. Is there a way to set it up in the BIOS to do that? Thanks.

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a b U Graphics card
a b V Motherboard
June 11, 2009 2:57:08 AM

dosilegecko said:
Hey All,
Would it be possible to put my graphics card in the secondary PCIe slot in my ASUS P6T deluxe v2?
I need both PCI slots and my 8800gtx takes up too much space. Is there a way to set it up in the BIOS to do that? Thanks.


No need to change anything, just pop it in. The first and second slots are both fed directly by the northbridge with a full set of 16 PCIe 2.0 lanes and have the same priority.

Now as for the THIRD x16 slot, well, the best it can do is steal half the lanes from the second slot.

So stick your card in the first or second slot and away you go.
June 11, 2009 3:15:49 AM

Thanks a bunch! I have my sound card in one PCI slot, and then I had to get a new firewire expansion slot because the built-in firewire has a chipset that is not fully compatible with my recording interface (yamaha N12). I was hoping to be able to keep my sound card installed and add the firewire, and now I know I can.

Thanks again.
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November 27, 2009 2:08:34 AM

I also wanted to know if I could put a PCI Express x16 graphics card into the second slot on ASUS P6T Deluxe V2. If you have a x8 PCI Express card then it really doesn't matter but a x16 PCIe card needs full x16 lanes (well, in theory). Basically all motherboard manuals I have read suggest we put a single card in the primary PCIe x16 connector for optimum performance.

I have put mine in the second (PCIe_2) connector and GPU-Z and other similar tools report that it is running at x16, so that is cool. But since PCIe_2 shares bandwidth with PCIe_3 I believe it also shares it with other PCIe slots (with PCIe x1 and PCIe x4). I don't have them, populated but still, I'd rather know to be sure it really runs at it's max capability. PCIe_1 is supposedly the only slot which always has x16 lanes dedicated.

Intel X58 supports 36 PCIe lanes. 16 are dedicated to the primary PCIe x16 slot so you're left with 20 lanes. Now if you put a PCIe x1 card in PCIe_3 slot and PCIe x4 card into PCIe x4 slot, you're left with 15 lanes which is what PCIe_2 will get. That's probably enough even for most higher class cards at the moment. But since you probably don't use all PCIe slots, the PCIe_2 will get its 16 lanes.

So I think they wrote that it the manual just to be on the safe side. In real world putting a card in the second PCIe slot will be just as good in the majority of all cases.

So that's my theory. :-) If I'm wrong and someone can correct me, please do so! I want to learn, too. :-)
a b U Graphics card
a b V Motherboard
November 27, 2009 2:57:26 AM

Perplexer said:
I also wanted to know if I could put a PCI Express x16 graphics card into the second slot on ASUS P6T Deluxe V2. If you have a x8 PCI Express card then it really doesn't matter but a x16 PCIe card needs full x16 lanes (well, in theory). Basically all motherboard manuals I have read suggest we put a single card in the primary PCIe x16 connector for optimum performance.

I have put mine in the second (PCIe_2) connector and GPU-Z and other similar tools report that it is running at x16, so that is cool. But since PCIe_2 shares bandwidth with PCIe_3 I believe it also shares it with other PCIe slots (with PCIe x1 and PCIe x4). I don't have them, populated but still, I'd rather know to be sure it really runs at it's max capability. PCIe_1 is supposedly the only slot which always has x16 lanes dedicated.

Intel X58 supports 36 PCIe lanes. 16 are dedicated to the primary PCIe x16 slot so you're left with 20 lanes. Now if you put a PCIe x1 card in PCIe_3 slot and PCIe x4 card into PCIe x4 slot, you're left with 15 lanes which is what PCIe_2 will get. That's probably enough even for most higher class cards at the moment. But since you probably don't use all PCIe slots, the PCIe_2 will get its 16 lanes.

So I think they wrote that it the manual just to be on the safe side. In real world putting a card in the second PCIe slot will be just as good in the majority of all cases.

So that's my theory. :-) If I'm wrong and someone can correct me, please do so! I want to learn, too. :-)


No, you're wrong. On most X58 motherboards (save for a weird EVGA model), two slots each have 16 unshared lanes.

The third x16 slot is where things get tricky: The BEST boards have a set of selector switches that allow the second and third slot to split the lanes as x8/x8, but ONLY when a card higher than x1 is inserted into the third slot. That's what the switches are for, to divert the lanes when needed, or not divert them when they aren't needed, by the third slot.

Cheaper X58 boards with three slots typically have x16/x16/x4 lanes, all permanently wired that way. They still share nothing.

EVGA has a board with one x16 slot and two x8 slots, but you don't have that board.

And no, you don't need sixteen lanes. Your card would work fine with eight lanes. But it doesn't need to work fine with eight lanes, because you have sixteen lanes that are not being shared with anything.
November 27, 2009 3:29:07 AM

Well I read you post 5 times I still don't exactly see where I was supposedly wrong.

This is a copy/paste from a Gigabyte GA-EX58-UD5 User Manual (page 12):

(Note 3) The PCIEX8_1 slot shares bandwidth with the PCIEX16_2 slot. When PCIEX8_1 is populated
with a PCI Express graphics card, the PCIEX16_2 slot will operate at up to x8 mode.


This probably means the board automatically assigns lanes between the second and the third PCIe slot. So this Gigabyte board clearly DOES share lanes. ASUS P6T Deluxe V2 also works the same way. I don't know about Gigabyte but the ASUS PT6 Deluxe V2 does have an option in BIOS to set the PCIe_2/PCIe_3 ratio to x16/x1.

But still, if X58 supprts 36 lanes, 16 of which ARE dedicated to PCIe_1, you're left with 20 lanes. Now if you populate the little black PCIe-x4 slot, you're left with 16 lanes available to the system. Now put another x1 card in PCIe_3 slot (for example a LAN adapter) and PCIe_2 has no choice but share one lane with PCIe_3 (even if I set it to x16/x1 in BIOS) and live with just 15 lanes, right ? That's why they say PCIe_2 is sharing with PCIe_3, isn't it ? Cause PCIe_2 will be left with only 15 lanes and not PCIe_1. So what's wrong with this logic (except that I can never populate PCIe_3 with anything cause my fat card in PCIe_2 is blocking it) ? I mean, explain. How are those 36 PCIe lanes distributed if I populate all the slots in my motherboard ?

We also never answered the question of why manufacturers always suggest that we use single cards in the "primary" PCIe_1 slot for optimal performance (be it ASUS PT6 Deluxe 2, Gigabyte GA-EX58-UD5, Intel DX58SO, ...). There must be some (at least theoretical) reason for that.
a b U Graphics card
a b V Motherboard
November 27, 2009 4:23:06 AM

Perplexer said:
Well I read you post 5 times I still don't exactly see where I was supposedly wrong.

This is a copy/paste from a Gigabyte GA-EX58-UD5 User Manual (page 12):

(Note 3) The PCIEX8_1 slot shares bandwidth with the PCIEX16_2 slot. When PCIEX8_1 is populated
with a PCI Express graphics card, the PCIEX16_2 slot will operate at up to x8 mode.


This probably means the board automatically assigns lanes between the second and the third PCIe slot. So this Gigabyte board clearly DOES share lanes. ASUS P6T Deluxe V2 also works the same way. I don't know about Gigabyte but the ASUS PT6 Deluxe V2 does have an option in BIOS to set the PCIe_2/PCIe_3 ratio to x16/x1.

But still, if X58 supprts 36 lanes, 16 of which ARE dedicated to PCIe_1, you're left with 20 lanes. Now if you populate the little black PCIe-x4 slot, you're left with 16 lanes available to the system. Now put another x1 card in PCIe_3 slot (for example a LAN adapter) and PCIe_2 has no choice but share one lane with PCIe_3 (even if I set it to x16/x1 in BIOS) and live with just 15 lanes, right ? That's why they say PCIe_2 is sharing with PCIe_3, isn't it ? Cause PCIe_2 will be left with only 15 lanes and not PCIe_1. So what's wrong with this logic (except that I can never populate PCIe_3 with anything cause my fat card in PCIe_2 is blocking it) ? I mean, explain. How are those 36 PCIe lanes distributed if I populate all the slots in my motherboard ?

We also never answered the question of why manufacturers always suggest that we use single cards in the "primary" PCIe_1 slot for optimal performance (be it ASUS PT6 Deluxe 2, Gigabyte GA-EX58-UD5, Intel DX58SO, ...). There must be some (at least theoretical) reason for that.


You're wrong because the board doesn't share lanes unless the other slot is filled. You're also wrong about the x1 slots, because those do not use any of the 36-lanes of the X58 Express Northbridge. The ICH10 Southbridge has six additional lanes which supply several x1 slots and onboard devices.

http://media.bestofmicro.com/3/T/166025/original/X58-bl...
November 27, 2009 5:01:03 AM

Crashman said:
You're wrong because the board doesn't share lanes unless the other slot is filled. You're also wrong about the x1 slots, because those do not use any of the 36-lanes of the X58 Express Northbridge. The ICH10 Southbridge has six additional lanes which supply several x1 slots and onboard devices.

http://media.bestofmicro.com/3/T/166025/original/X58-bl...


Why do you think the manufacturers suggest that we put our cards in PCIe_1 for optimal performance ? ASUS P6T Deluxe V2 is supposed to be a good board but they still suggest using PCIe_1 for single card configuration ? Why is that ?
a b U Graphics card
a b V Motherboard
November 27, 2009 5:12:12 AM

Perplexer said:
Why do you think the manufacturers suggest that we put our cards in PCIe_1 for optimal performance ? ASUS P6T Deluxe V2 is supposed to be a good board but they still suggest using PCIe_1 for single card configuration ? Why is that ?


It's probably the first slot scanned by BIOS when you start your computer. It's also closer to the Northbridge, which reduces latency and increases signal stregth by an incredibly small amount.
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