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Dual 8x on Mobo

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September 3, 2010 6:29:22 AM

I've been looking around for an 1156 mobo with dual 8x for a new build. I don't intend to use the second slot right off the bat, but I want the option for SLI for an upgrade path. I've noticed boards take a fairly decent price jump from 16x/4x to 8x/8x.

For example:
http://www.newegg.com/Product/Productcompare.aspx?Submi...|13-131-601^13-131-601-TS%2C13-131-404^13-131-404-TS

Is the cause in the big difference in price of these two boards the dual 8x option? Or am I missing something else the second board offers over the first that would warrant such a difference in price?

More about : dual mobo

a c 135 V Motherboard
September 3, 2010 7:57:05 AM

If they had PCI-E 1.0 slots, i would have recommended going with dual 8x,because there is a noticeable difference between them,however PCI-E 2.0 seems to have an effect on CF performance,and judging from benchmarks,the difference between 16x4x and dual 8x isn't huge.
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September 3, 2010 1:02:29 PM

Maziar said:
If they had PCI-E 1.0 slots, i would have recommended going with dual 8x,because there is a noticeable difference between them,however PCI-E 2.0 seems to have an effect on CF performance,and judging from benchmarks,the difference between 16x4x and dual 8x isn't huge.


I thought the difference from 16x/16x to 8x/8x wasn't huge. Only like 5% performance loss. What I've seen was 16x/16x to 16x/4x was quite a bit more.
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a c 135 V Motherboard
September 3, 2010 6:17:20 PM

You are right but I wasn't talking about dual 16x and dual 8x, i was talking about dual 8x and 16x4x.
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September 3, 2010 9:17:34 PM

Isn't dual 8x better then 16x/4x?
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a b V Motherboard
September 3, 2010 9:23:44 PM

MrMooky said:
Isn't dual 8x better then 16x/4x?


Yes but the degree to which it will be a slowdown depends on the PCI-e version (if 1.0 then it will be very noticeable but if 2.0 then the difference is less noticeable as the PCI-e 2.0 x4 standard is the same throughput as a PCI-e 1.0 x8 connection !) -- so a PCI-e 2.0 version MOBO with x16\x4 slots will still perform the same as a PCI-e 1.0 MOBO with x8\x8 and most current video cards will not be bottlenecked too badly at that throughput speed.
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September 3, 2010 9:39:59 PM

JDFan said:
Yes but the degree to which it will be a slowdown depends on the PCI-e version (if 1.0 then it will be very noticeable but if 2.0 then the difference is less noticeable as the PCI-e 2.0 x4 standard is the same throughput as a PCI-e 1.0 x8 connection !) -- so a PCI-e 2.0 version MOBO with x16\x4 slots will still perform the same as a PCI-e 1.0 MOBO with x8\x8 and most current video cards will not be bottlenecked too badly at that throughput speed.



I'm confused.
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a b V Motherboard
September 3, 2010 10:03:17 PM

MrMooky said:
I'm confused.


THe PCI-e standard is now on revision 2.0 which has increased the throughput at a single speed to double what it used to be -- so an older MOBO that follows the PCI-e 1.0 standard will be running at half the throughput of a newer board that follows the 2.0 standard - so a PCI-e x8 slot on an older MOBO that uses the PCI-e 1.0 standard slot will be identical in throughput to a PCI-e x4 slot on a newer MOBO that uses the PCI-e 2.0 standard and a PCI-e 2.0 x8 slot will be equal to an older PCI-e 1.0 x16 slot.

So when evaluating the amount of speed difference in throughput you also need to consider whether the MOBO is PCI-e 1.0 or 2.0 in order to figure if the x4 speed will be a bottleneck. A MOBO using PCI-e 1.0 with x16\x4 slots will slowdown the performance but a PCI-e 1.0 with x8\x8 will only marginally if at all slow performance on current cards but a newer MOBO using the PCI-e 2.0 standard running either x16\x4 or x8\x8 will have little to no effect on the speed (since the new standard x4 throughput is equal to the old x8 speed !)

In summary :

PCI-e 1.0 x4 --- will effect performance on most high end GPU's
PCI-e 1.0 x8 = PCI-e 2.0 x4 --- and both may effect performance a small amount
PCI-e 1.0 x16 = PCI-e 2.0 x8 --- will have no impact on GPU performance since the GPU can not saturate that pipeline
PCI-e 2.0 x16 --- Twice the throughput of PCI-e 1.0 x16 so provides more than enough throughput for any modern GPU
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a c 135 V Motherboard
September 4, 2010 6:33:45 AM

MrMooky said:
Isn't dual 8x better then 16x/4x?

For PCI-E 1.0
Dual 16x > dual 8x > 16x4x.
The difference between the first 2 isn't much,(like 4% maximum), but both are significantly faster than 16x4x.
For PCI-E 2.0
Dual 16x > dual 8x > 16x4x
Because of PCI-E 2.0,the difference between all 3 configurations isn't much(unlike PCI-E 1.0 in which the first 2 were significantly faster than 16x4x)
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a b V Motherboard
September 4, 2010 6:52:29 AM

JDFan said:
Yes but the degree to which it will be a slowdown depends on the PCI-e version (if 1.0 then it will be very noticeable but if 2.0 then the difference is less noticeable as the PCI-e 2.0 x4 standard is the same throughput as a PCI-e 1.0 x8 connection !) -- so a PCI-e 2.0 version MOBO with x16\x4 slots will still perform the same as a PCI-e 1.0 MOBO with x8\x8 and most current video cards will not be bottlenecked too badly at that throughput speed.

The boards he's looking at are either x8/x8 in PCIe 2.0 or x16/x4 with the x4 slot at PCIe 1.1 speed.
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