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Intel Z77 extra PCIe x4 slot
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deltatux
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Default Intel Z77 extra PCIe x4 slot - 04-14-2012, 22:26 | posts: 19,055 | Location: Toronto, Canada

Hey guys,

I'm trying to understand these new Z77 motherboards coming out with the extra PCIe x16 slots running at x4 mode. According to the ASUS P8Z77-V motherboard manual which is in French (there's no English manual to download which is weird).

It states:
Quote:
Originally Posted by ASUS P8Z77-V Manual in French
Le slot PCIe x16_3 partage sa bande passante avec le slots PCIe x1_1 et PCIe x1_2 et le connecteur SATA6G_E12. Le mode lien par défaut du slot PCIe x16_3 est défini sur x1.
Which translates to:
Quote:
Originally Posted by English Translation
The PCIe x16_3 slot shares its bandwidth with the PCIe x1_1 and PCIe x1_2 slots and the SATA6G_E12 connector. The default link mode of the PCIe x16_3 slot runs at x1 speed.
So does that mean that if I slot a PCIe x4 card in the PCIe x16_3 slot, then the other PCIe x1 would not work? Conversely, If I slip a PCIe x1 in the first slot, would the PCIe x16_3 work at x4 or would it downgrade to X1 regardless?

If so, then why the hell did they bother putting another PCIe x16 slot there, I find it kind of useless if I insert a card there and it disables the other PCIe slots.

deltatux
   
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Default 04-14-2012, 23:13 | posts: 17,829 | Location: New Jersey, USA

Look for a review on that MB maybe. My 3 pcie slots are 2x8x with sli and 1 4x slot I think
   
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fr33k
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Default 04-15-2012, 02:25 | posts: 1,822 | Location: USA

if its like my old one it forces the 16x to run at 8x.
   
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deltatux
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Default 04-15-2012, 02:41 | posts: 19,055 | Location: Toronto, Canada

Quote:
Originally Posted by fr33k View Post
if its like my old one it forces the 16x to run at 8x.
No no man, the PCIe x16 slot at the very bottom of these boards function at only x4.

Here's an example from the ASUS P8Z77-V motherboard which I'm thinking of getting:


See how the bottom PCIe x16 slot is there? So I'm confused on how it works. Does it mean that when PCIe x1_1 and PCIe x1_2 are plugged in PCIe x16_3 runs at x1 speed and if I slip in a PCIe x4 card there, it disables both the PCIe x1 slots?

Apparently they're shared from what I'm reading.... can anyone confirm?

deltatux
   
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fr33k
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Default 04-15-2012, 04:00 | posts: 1,822 | Location: USA

I meant the same- Link mode forced mine at 8x instead of 16x no matter what as long as it was in link mode. Judging by the translation link mode with any added cards simply makes it 1x.
   
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Default 04-15-2012, 05:40 | posts: 19,055 | Location: Toronto, Canada

Quote:
Originally Posted by fr33k View Post
I meant the same- Link mode forced mine at 8x instead of 16x no matter what as long as it was in link mode. Judging by the translation link mode with any added cards simply makes it 1x.
So I don't get why these board manufacturers put a x16 slot there if it's going to run x1 anyways >.>"

Thanks man

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Default 04-15-2012, 06:29 | posts: 23,629 | Location: NZ

Quote:
Originally Posted by deltatux View Post
So I don't get why these board manufacturers put a x16 slot there if it's going to run x1 anyways >.>"

Thanks man

deltatux
That French manual is wrong or else it's been translated incorrectly.
The PCIe x1_2 shares it's bandwidth with SATA6G_E12 and the black slot runs at x4 mode.

http://www.asus.com/Motherboards/Int...specifications

Last edited by Pill Monster; 04-15-2012 at 06:33.
   
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deltatux
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Default 04-15-2012, 06:54 | posts: 19,055 | Location: Toronto, Canada

Quote:
Originally Posted by Pill Monster View Post
That French manual is wrong or else it's been translated incorrectly.
The PCIe x1_2 shares it's bandwidth with SATA6G_E12 and the black slot runs at x4 mode.

http://www.asus.com/Motherboards/Int...specifications
That's what it's written and that's what I translated from French to English (no I didn't use a translation service).

EDIT: I'm guessing since the two PCIe x1 slots shares bandwidth from that PCIe 2.0 x16 slot at the bottom of the board, it by extension shares data with that SATA 3 port.

I do believe that by default that bottom slot runs at x1 speed, even ASUS's Sabertooth Z77 manual states that:
Quote:
Originally Posted by ASUS Sabertooth Z77 Manual
The PCIe 2.0 x16 slot shares bandwidth with PCIe 2.0 x1_1 slot, PCIe 2.0 x1_2 slot, and PCIe 2.0 x1_3 slot. The PCIe 2.0 x16 slot default setting is in x1 mode.
deltatux

Last edited by deltatux; 04-15-2012 at 07:06.
   
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Default 04-15-2012, 07:25 | posts: 7,068

Why don't you just read the specs from the mobo's website form Asus?

2 x PCIe 3.0/2.0 x16 (x16 or dual x8)
1 x PCIe 2.0 x16 (x4 mode, black)
2 x PCIe 2.0 x1
2 x PCI

And anyway, sandy and ivy bridge have 16 pcie lanes on the CPU, the rest of the lanes are on the Z77 chipset. Look at these block diagrams for the Z77 chipset:



And BTW, intel lied about series 7 boards supporting pcie gen 3, it was never meant for the chipset, only Ivy Bridge has those 16 pcie gen 3 lanes!
   
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Default 04-15-2012, 07:42 | posts: 23,629 | Location: NZ

Quote:
Originally Posted by deltatux View Post
That's what it's written and that's what I translated from French to English (no I didn't use a translation service).

EDIT: I'm guessing since the two PCIe x1 slots shares bandwidth from that PCIe 2.0 x16 slot at the bottom of the board, it by extension shares data with that SATA 3 port.

I do believe that by default that bottom slot runs at x1 speed, even ASUS's Sabertooth Z77 manual states that:


deltatux
It runs at x4.

Edit-
This might help...


Quote:
The two PCI Express 3.0/2.0 x16 slots are controlled by the CPU, with the first slot working at x16 when only one video card is installed, and with both working at x8 when two video cards are installed.
Since these slots are controlled by the CPU, they will offer PCI Express 2.0 bandwidth (8 GB/s at x16) when a “Sandy Bridge” CPU is installed, but PCI Express 3.0 bandwidth (16 GB/s at x16) when an “Ivy Bridge” CPU is used.
The third PCI Express x16 slot is 2.0 and always work at x4 speed.

In order to properly accommodate the additional PCI Express devices that are on this motherboard (third PCI Express x16 slot, additional Gigabit Ethernet port, Wi-Fi/Bluetooth card, two extra SATA-600 ports, and four extra USB 3.0 ports), the board makes use of a PLX PEX8608 switch chip.
This chip automatically switches the available PCI Express lanes to the devices that need them.
http://www.hardwaresecrets.com/artic...erboard/1528/2

Last edited by Pill Monster; 04-15-2012 at 08:12.
   
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Default 04-15-2012, 08:08 | posts: 289 | Location: the internets

Quote:
Originally Posted by deltatux View Post
Hey guys,

I'm trying to understand these new Z77 motherboards coming out with the extra PCIe x16 slots running at x4 mode. According to the ASUS P8Z77-V motherboard manual which is in French (there's no English manual to download which is weird).

It states:


Which translates to:


So does that mean that if I slot a PCIe x4 card in the PCIe x16_3 slot, then the other PCIe x1 would not work? Conversely, If I slip a PCIe x1 in the first slot, would the PCIe x16_3 work at x4 or would it downgrade to X1 regardless?

If so, then why the hell did they bother putting another PCIe x16 slot there, I find it kind of useless if I insert a card there and it disables the other PCIe slots.

deltatux
yes pretty much..i have a p8p67 and when i put anything in the 4x slot, i can either run it at 4x or at 1x...at 4x the second usb 3 controller and the pcie 1x slot stop working
   
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Default 04-15-2012, 12:07 | posts: 4,628 | Location: Not Far North Enough (England)

You've automatically got a mix of gen2 and gen3, 8 of one from the SB and 16 of the other from the "NB"/CPU. My guess would be that the 2 x1's and the x4 are from the SB. ASUS aren't very helpful about disclosing what's connected to what in PCIe, I've been trying to get some info out of em for ages but they reall'y aren't very helpful on the matter.
   
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deltatux
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Default 04-15-2012, 17:51 | posts: 19,055 | Location: Toronto, Canada

Quote:
Originally Posted by Pill Monster View Post
It runs at x4.

Edit-
This might help...

So ASUS is essentially wrong on their own manual O.o?? That doesn't make sense, this is getting confusing...

deltatux
   
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Default 04-15-2012, 19:34 | posts: 4,628 | Location: Not Far North Enough (England)

Going off that deltatux, it looks like the 16 Gen3 lanes off the CPU are splittable into x8/x8 and that bottom x4 slot is coming off the SB. IIRC X77 allows the 16 lanes to be split x8/x4/x4, but theres an additional x4 from the SB as well. You've probably got a few extra controllers stuck on the SB, hence the 8 going down to 4.
   
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Default 04-15-2012, 19:47 | posts: 16,072 | Location: US East Coast

Quote:
Originally Posted by deltatux View Post
So ASUS is essentially wrong on their own manual O.o?? That doesn't make sense, this is getting confusing...

deltatux
That's been known to happen....
   
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BLEH!
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Default 04-15-2012, 22:12 | posts: 4,628 | Location: Not Far North Enough (England)

Quote:
Originally Posted by sykozis View Post
That's been known to happen....
At least Gigabyte have the decency to whack a block diagram in their manuals. ASUS have been less than helpful in providing one for my motherboard.
   
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Default 04-17-2012, 03:58 | posts: 16,072 | Location: US East Coast

Quote:
Originally Posted by BLEH! View Post
At least Gigabyte have the decency to whack a block diagram in their manuals. ASUS have been less than helpful in providing one for my motherboard.
If I had a nickel for every time Asus has been "less than helpful"....I'd be retired already....lol

My HD7870 is the first time they've even been remotely helpful....

After-sale support is the main reason I stick with ASRock....
   
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Default 04-17-2012, 12:13 | posts: 4,628 | Location: Not Far North Enough (England)

Quote:
Originally Posted by sykozis View Post
If I had a nickel for every time Asus has been "less than helpful"....I'd be retired already....lol

My HD7870 is the first time they've even been remotely helpful....

After-sale support is the main reason I stick with ASRock....
This is why I was wary about getting an ASUS board, but I can't fault it thus far. If I do have any problems, though I'll just take it back to Scan, who've been more than helpful in recent years with faulty stuff. I'm just wary about going back to Gigabyte after 2 X58-UD3Rs died on me, but that coulda been a PSU issue. ASUS do make good stuff, just don't fix it well when they need to.
   
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Default 04-21-2012, 15:56 | posts: 4,826 | Location: Land of the Great Downunder

Quote:
Originally Posted by Sash View Post
Why don't you just read the specs from the mobo's website form Asus?

2 x PCIe 3.0/2.0 x16 (x16 or dual x8)
1 x PCIe 2.0 x16 (x4 mode, black)
2 x PCIe 2.0 x1
2 x PCI

And anyway, sandy and ivy bridge have 16 pcie lanes on the CPU, the rest of the lanes are on the Z77 chipset. Look at these block diagrams for the Z77 chipset:



And BTW, intel lied about series 7 boards supporting pcie gen 3, it was never meant for the chipset, only Ivy Bridge has those 16 pcie gen 3 lanes!
actually, you still need a motherboard that supports pcie3.0. if you run ivy bridge on a p67/z68 board that doesnt support pcie3.0, then it will run at pcie2.0. motherboard must have all the hardware required to support pcie3.0 for ivy bridge to use its pcie3.0 lanes.
   
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Default 04-22-2012, 06:55 | posts: 797 | Location: Orange County, CA

There are 16 3.0 lanes available from the CPU. The first 8 of those lanes connect directly to the PCIe1 socket, the other 8 lanes go to a PLX bridge chip.

When only one PCIe slot is populated, those 8 lanes are routed back to the PCIe1 socket to give it a full 16 lanes.

When the second slot is also populated, the 8 lanes from the PLX chip are routed instead to the PCIe2 socket.

This is also how Z68 works. The Z77 chipset also adds the ability to route 4 lanes from the PLX chip to an optional Thunderbolt controller, making PCIe2 x4. This is what is noted in the block diagram.

The Z77 chipset itself also has pcie lanes, but they are all 2.0 lanes. These lanes are used to add additional SATA controllers (like Marvell) or a second gigabit NIC, but 4 lanes can also be routed to PCIe3.

Some manufacturers will disable some addons if you plug something into that PCIe3, because there are only 8 lanes to go around. The higher end ASUS boards us another PLX chip to intelligently switch lanes to where they are needed, when bandwidth is needed, so that plugging in pcie3 doesn't deactivate a pair of SATA ports or something.
   
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Default 04-22-2012, 16:33 | posts: 7,068

nevermind, just woke up and did not read correctly

Last edited by Sash; 04-22-2012 at 16:37.
   
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