Z68 board with PCIE flexibility

I

Ice Nine

Limp Gawd
Joined
Aug 17, 2004
Messages
162
Yesterday I purchased an Asus Z68 board (the P8Z68-V PRO). I also picked up a Revodrive X2 240GB which is an x4 card.

In total I have three cards I want to use:

GTX 580 x16 (duh)
Revodrive, x4
Soundblaster Plat, x1

This board has:

2 x PCIe 2.0 x16 (x16 or dual x8, if you use the 2nd x16 slot, both drop to x8)
1 x PCIe 2.0 x16 (x4 mode or x1 mode, makes no sense to me why they'd use an x16 slot here though )
2 x PCIe x1

So basically, I have these choices in the bios:

Auto mode: the "x4/x1" mode PCIE x16 slot operates in x1 mode. Soundcard would have to live here. No matter what, i'm stuck with my GPU being at x8.

X4 mode: the "x4/x1" mode PCIE x16 slot operates in x4 mode. I could put my SSD here, but that would DISABLE the remaining x1 slots, leaving nowhere for my Soundcard to live.

X1 mode: the "x4/x1" mode PCIE x16 slot operates in x1 with all slots enabled, but with USB3 disabled - this still sucks as my SSD would be limited to x1 speeds if I put it in this slot, and would still limit my graphics card to x8.

So my question is - are there any SB boards out there that don't have these limitations, or do all of them have these limitations in some form or another? Also, how much am I hurting performance with a GTX580 being limited to x8?
 
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Generally 8X on the video card isn't a huge deal on PCIe 2.0. Your 580 really shouldn't be swapping back to ram.

Your issue is that Z68 has 24 lanes period. The normal allocation is 16 dedicated to video put to 1 or 2 slots, then 8 lanes of PCI-E to spread across other slots usually in 1x or 4x slots and onboard devices such as your USB 3.0 ports. This is a limitation of Z68.
 
Desktop sandy bridge LGA1155 has 16 lanes from the CPU and 8 from the PCH.

The CPU lanes are pretty much always used for either one x16 slot or two x8 slots (often with pathway switches to give the user the choice). The PCH lanes are used for other slots and for onboard perhiperhals. Some boards have some of the onboard stuff and/or x1 slots behind a PCIe bridge chip which allows more of the chipset's lanes to be dedicated to slots. An example of such a board is the asus P8P67 deluxe (I don't know if there is a z68 eqivilent).

This could in theory bottleneck the onboard stuff that is behind the bridge but unless you are heavilly loading everything at the same time it shouldn't be an issue.

Some boards also have the lanes from the CPU taken to a bridge chip but generally you only want such a board if you are doing setups with 3+ GPUs. Examples of such a boards include the ASUS P8P67 WS revoloution and the gigabyte UD7 (which comes in both P67 and Z68 versions).

Unfortunately most desktop board vendors don't supply block diagrams (gigabyte is the only one i'm aware of that does supply them) so it takes a fair bit of experiance and reading between the lines to figure out the PCIe configuration of any given board.
 
Thanks for the info plugwash. I've been wondering about this for a while now.
 
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