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Old 01-18-2013, 05:29 PM   #1
runzwithsizorz
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Default Single card lower slot still x16?

With a mobo that has 2 slots, 1 labeled PCIe 3.0/2.0x16 (single at x16 or dual at x8/x8 mode), and the other labeled PCIe 3.0/2.0x16 (at x8 mode).
For air flow, and aesthetics reasons with a single card set up, can the other slot be used and still retain x16? If not, then why the hell is it labeled x16?
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Old 01-18-2013, 05:33 PM   #2
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No. You can confirm this simply by running GPU-z with the card installed, which will tell you the speed of the PCIe link.

Don't know why it's labeled as x16, but the second slot will always be x8. If you're running a PCIe 3.0 card, it won't be a bottleneck. Even for a fast PCIe 2.0 card the bottleneck won't be that significant.
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Old 01-18-2013, 05:44 PM   #3
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It's nothing to worry about if you are at x8. You could even try back-to-back benchmarks.

Would you mind if your card dropped from 100 fps at x16 down to 99 fps at x8?
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Old 01-18-2013, 06:12 PM   #4
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So obviously I have so much to learn. But I thought that there were some mobos that had 2, or 3 slots with full x16 though-put? So are you saying that if I use that *other* slot, (not as cramped, and more air flow), I will not notice any difference?
7870 on a Asus p8z77 v pro. A gaming build for Mz Runz
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Old 01-18-2013, 06:22 PM   #5
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PCIe 3.0 x8 bandwidth will be more than sufficient for a 7870.
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Old 01-18-2013, 07:47 PM   #6
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Quote:
Originally Posted by Termie View Post
PCIe 3.0 x8 bandwidth will be more than sufficient for a 7870.
Thankz, but someday I hope to learn the why's. I have been out of the loop for quite a spell. For me, I do not just want to assemble, I want to learn why this, or that works. Alas, the Mz is growing impatient waiting so my education will have to wait. 2 of the components used in her build is the p/p CM hyper212 plus, and the Seasonic x-650, so perhaps I am doing something right
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Old 01-18-2013, 08:02 PM   #7
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Quote:
Originally Posted by runzwithsizorz View Post
Thankz, but someday I hope to learn the why's. I have been out of the loop for quite a spell. For me, I do not just want to assemble, I want to learn why this, or that works. Alas, the Mz is growing impatient waiting so my education will have to wait. 2 of the components used in her build is the p/p CM hyper212 plus, and the Seasonic x-650, so perhaps I am doing something right
This article should help clear some things up for you: http://www.anandtech.com/show/5458/t...cking-and-msaa

And yes, those are some nice parts you have there.
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Old 01-19-2013, 04:44 AM   #8
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Check your motherboard's manual. There should be block diagram and instructions on how on-board PCIe slots are configured. Every boards are different, so you should make sure what's what.

I've been doing for a long time what you're planning to do. If something doesn't work as expected (i.e. nearly identical performance), the most likely fault lies on the board. Then the chipset/video drivers.
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Old 01-19-2013, 05:09 AM   #9
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Quote:
Originally Posted by runzwithsizorz View Post
For air flow, and aesthetics reasons with a single card set up
Why do you think airflow would be improved by having the card in the lower slot?

Quote:
can the other slot be used and still retain x16? If not, then why the hell is it labeled x16?
I would guess it's because the slot is physically capable of x16, but electrically limited to x8
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Old 01-19-2013, 10:37 AM   #10
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Quote:
Originally Posted by Termie View Post
No. You can confirm this simply by running GPU-z with the card installed, which will tell you the speed of the PCIe link.

Don't know why it's labeled as x16, but the second slot will always be x8. If you're running a PCIe 3.0 card, it won't be a bottleneck. Even for a fast PCIe 2.0 card the bottleneck won't be that significant.
All three of my physical x16 slots are electrically x16. Not sure where you are getting your info from.
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Old 01-19-2013, 10:49 AM   #11
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I believe 2011 Motherboards support multiple X16 usage.
For Sandy Bridge/Ivy Bridge the number of lanes available is limited by the on chip control.
Some motherboards use additional on board support I think?
Anyway looking at the solder side of the motherboard x16 slot with all contacts soldered does x16, when a section is absent, it is x8, have not checked x4.
FWIW 3.0 x16 carries twice the bandwith of 2.0x16 so even a 2.0x16 at x4 will carry an SLI set up (which require 2.0x16 x8 minimum).
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Old 01-19-2013, 10:50 AM   #12
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Quote:
Originally Posted by lehtv View Post
Why do you think airflow would be improved by having the card in the lower slot?

The 4+ inch HSF nearly sits on top of the card. Also have 2 side case fans
blowing straight at the mobo. IMO, components run, or are cooled better
when they are not all bunched together. And it just looks better



I would guess it's because the slot is physically capable of x16, but electrically limited to x8
Would still like to learn more about this, manual did not address this.
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Old 01-19-2013, 11:48 AM   #13
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Quote:
Originally Posted by lehtv View Post
Why do you think airflow would be improved by having the card in the lower slot?

I would guess it's because the slot is physically capable of x16, but electrically limited to x8
I've already made a similar change, moving my card from the lower x16 slot to the upper x8 slot.

The reason is that the lower slot was next to the power supply, so it restricted airflow and also created a pocket of super-heated air (like a dead space without a good way for the hot air to escape away from the cavity between the power supply and the card, toward the rear of the case).

So my overclocks were limited on the video card; I had to artificially limit my overclock due to heat instability, not to mention my power supply was getting cooked by the video card.

Anyway, by moving my card to the upper slot, that gave it lots of space and eliminated any dead air, everything circulated nicely, and I got a much better overclock. So even though I went from an x16 slot to an x8 slot, I actually got *better* performance because everything ran cooler and I could achieve higher stable GPU overclocks. The overclock simply dwarfed any miniscule reduction the x8 interface caused.

But my motherboard is an older Asus 890GX that has this funky setup where the lower slot is x16 and the upper is x8, I don't think most motherboards are like that.
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