6870 Crossfire with 4x Slot?

[Smartazz]

I currently have the rig in my sig with a single 6870. If I see a good price on a 6870 I'm tempted to grab one. My motherboard only support the second PCI-e at 4x and I don't have a Crossfire bridge. I've also heard reports that this motherboard's second PCI-e and SATA ports use the same bandwidth, is this true and would it be a problem? I'm aware that multi GPU has its drawbacks, but I principally want to run my games(particularly BF3) at a constant 60fps. There shouldn't be microstutter as long as the frame rate is above the refresh rate, correct? All in all, is it worth grabbing another 6870?

Edit: Resolution in 1920 by 1080.

 

[Don Karnage]

Imo I wouldn't spend money on another card then run it in a X4 slot

 

[Smartazz]

I've been doing some searching and I've heard about 10% degradation in performance. However, 6870s scale extremely well in Crossfire, so my frame rates should be really high anyway.

 

[superjim]

Why Biostar didn't split the PCIe 2.0 lanes into two x8 I'll never know. If a board has more than one PCIe 2.0 slot, it should default to x16 for one populated, x8 for two. Does it cost that much more to configure the mobo like that?

 

[Smartazz]

Biostar isn't the only manufacturer who does that. It's not uncommon on P67 and Z68 motherboards.

 

[Termie]

Here are some benches for you: http://www.tomshardware.com/reviews/pci-express-scaling-p67-chipset-gaming-performance,2887-10.html

Honestly, it's probably worth a try - if the worst case is 25% below optimal scaling, it's still pretty darn good (say 70%), which would be enough to get you to 60fps in BF3 at high/ultra.

That's how I run my 5850 crossfire setup (vsync on).

P.S. I'm not sure why you mentioned that you don't have a crossfire bridge. You'll obviously need one, so if the card you find doesn't include one, just buy it separately.

 

[notty22]

Why Biostar didn't split the PCIe 2.0 lanes into two x8 I'll never know. If a board has more than one PCIe 2.0 slot, it should default to x16 for one populated, x8 for two. Does it cost that much more to configure the mobo like that?

It's how they make distinctions in their product line. It's probably a logic switch that cost pennies. But they don't include it, unless they are also going to include SLI support. Which they have to pay Nvidia a fee for.

Most AMD cards come with a crossfire bridge. If it's in the picture contents it should come.

 

[Smartazz]

I mentioned the lack of a Crossfire bridge because I was under the impression that motherboards tend to come with them. They're really cheap anyway. Another question, should I buy the exact same card? Also, can I use a non-reference card with a reference card?

 

[Termie]

I mentioned the lack of a Crossfire bridge because I was under the impression that motherboards tend to come with them. They're really cheap anyway. Another question, should I buy the exact same card? Also, can I use a non-reference card with a reference card?

Higher-end motherboards come with crossfire connectors. Not a problem - you can get one aftermarket. You can buy any 6870 you want - you don't need the same model. I'm not seeing one that includes the crossfire bridge, so just get the cheapest: http://www.newegg.com/Product/Produc...82E16814161389

$140AR/FS for that HIS model is a great deal.

 

[Smartazz]

Higher-end motherboards come with crossfire connectors. Not a problem - you can get one aftermarket. You can buy any 6870 you want - you don't need the same model. I'm not seeing one that includes the crossfire bridge, so just get the cheapest: http://www.newegg.com/Product/Produc...82E16814161389

$140AR/FS for that HIS model is a great deal.

I'm thinking about selling my Bitcoins to buy the card so it'll cost me next to nothing to upgrade. However, I gotta run the Bitcoin client to get access to the coins I mined a few months ago. Will there be an opportunity to buy a 6870 cheaply in the next few months? I'm in no rush, so I can wait a bit.

 

[notty22]

IMO, I'd probably buy and enjoy now. Eventually the 28nm parts are going to start replacing the 40nm 6870. Right now, they are probably at their cheapest, and like the gtx 460 will only start creeping up in price as they get scarce.

 

[Smartazz]

The 4870 and GTX 260 are very cheap now. You don't think the 6870 will do the same thing?

 

[Termie]

The 4870 and GTX 260 are very cheap now. You don't think the 6870 will do the same thing?

The 4870 recently reappeared after a long hiatus, probably based on the uncovering of old stock, and the GTX260 is no longer sold (at least not new).

Sure, the 6870 might be available six months or a year from now, but playing the waiting game on it might be pushing your luck. Even the 5850/5870 are gone from the market and have been for 4 months or so. There's no reason the 6870 would stick around longer than those cards did. Given that the 6870 came out a year later, at best you probably have until the end of summer 2012 to get one, but given the transition to a new manufacturing method, I'd say that's optimistic.

 

[Smartazz]

What exactly does electrical 4x PCI-e mean? Btw, the manual also says that the second PCI-e slot is PCI 1.0 4x. Does this change anything?

 

[VirtualLarry]

What exactly does electrical 4x PCI-e mean? Btw, the manual also says that the second PCI-e slot is PCI 1.0 4x. Does this change anything?

That means that the second PCI-E slot is driven off of the southbridge chip. Which means that it shares bandwidth with the SATA/USB.

If it were PCI-E 2.0 x4, then it might be ok (like 10% framerate loss), but PCI-E 1.0 x4? That's pretty slow.

 

[TakeNoPrisoners]

That means that the second PCI-E slot is driven off of the southbridge chip. Which means that it shares bandwidth with the SATA/USB.

If it were PCI-E 2.0 x4, then it might be ok (like 10% framerate loss), but PCI-E 1.0 x4? That's pretty slow.

That would be like PCI-E 2.0 x2 which doesn't even exist.

 

[Smartazz]

I'm having trouble finding a reference HD 6870. I want voltage control and I think the reference models are the only ones with it. Does this card look reference to you? http://www.amazon.com/HIS-Mini-Displ...6045052&sr=1-3

 

[TakeNoPrisoners]

I'm having trouble finding a reference HD 6870. I want voltage control and I think the reference models are the only ones with it. Does this card look reference to you? http://www.amazon.com/HIS-Mini-Displ...6045052&sr=1-3

This is a reference 6870.

So is this.

Id go for the Diamond card because it is cheaper.

 

[Kenmitch]

I'm having trouble finding a reference HD 6870. I want voltage control and I think the reference models are the only ones with it. Does this card look reference to you? http://www.amazon.com/HIS-Mini-Displ...6045052&sr=1-3

Easy way to tell is look for black pcb with the AMD logo that is silkscreened above the pci-connector when viewing photos of the card.

 

[Smartazz]

If reference costs that much more, i'll go with a non reference. Which is the best one for around $160?

 

[MagnusTheBrewer]

PCI Express 4x max bandwidth is 2000 MB/s
A 6870 running stock speeds uses a bandwidth of 134.4gb/s In Crossfire, they would use less than double that bandwidth so, using the 4x slot should be fine with only minimal frame loss as was borne out in the articles over at [H]

 

[Smartazz]

I think max bandwidth is 1000MB/s.
http://en.wikipedia.org/wiki/PCI_Express

 

[MagnusTheBrewer]

I think max bandwidth is 1000MB/s.
http://en.wikipedia.org/wiki/PCI_Express

You are correct. PCI 1.0 4x is 1000 MB/s However, my point and the articles at [H] are still valid.

 

[MagnusTheBrewer]

Are you sure your manual says PCI 1.0? On the Biostar site and others every mention of the TZ68A+ refers to it as having PCI 2.0 However, Biostar doesn't doesn't say the "RCH" part (just the other review sites). Biostar lists version 6.0, is that the same board?

 

[Smartazz]

The RCH simply means that it comes with a remote control and HDMI cable. Other than that, I'm pretty sure it's the exact same board.