X48 vs P45 vs P35 chipset for Crossfire

Grit

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Nov 9, 2002
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Does the bandwidth on your PCIe x16 slots matter for Crossfire on the new AMD 4850 or 4870 cards?

I'm currently running a P35 chipset motherboard (two x16 slots, but one only runs at x4 speed). Just wondering if I would benefit from a 2x8 board (P45 chipset) or a 2x16 board (X48 chipset) (assuming I'm understanding all this correctly).

Sorry, I searched and couldn't find the answer. :(
 

JPB

Diamond Member
Jul 4, 2005
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I would go with the *X* board without a doubt. Like the X48. I just read an article yesterday ( Ill see if I can find it again and link you to it ) that showed a considerable gain in performance for the X series over the P series.

Edit:

The article is here. From TweakTown

Final Thoughts for the article


This is really a very interesting article and is something people need to be taking note of. The first thing you need to be checking is if you're reading a review where Crossfire is being tested. Make sure that the board there using is a x16 / x16 motherboard. The results really do speak for themselves and it?s clear that there is a performance difference between a x16 / x16 configuration which the X48 offers, and the x8/x8 one on the P45.

If you?re really thinking about going down the Crossfire path, we would be highly recommending that you spend the extra money to go to an X38 or X48 based motherboard over the P45. Of course, if you?re not then it doesn?t really matter. With one card the P45 runs at x16, which is exactly what you want.

The thing is, the X48-DQ6 is only about 10% more expensive, so you could easily say that you should just spend the extra money and get that. You may in future go Crossfire without knowing it yet, but admittedly the P45-DQ6 does have some very cool features such as the new ICH10R controller, loads of SATA ports and just some really funky new add-ons like the power buttons on board. Of course, we will cover all these in more detail in our full motherboard review at a later date.

Before you rush out and buy that P45 board thinking that x8 / x8 will be just fine, sit back and have a think if you?re really aiming to go down the Crossfire path in the near future.
 

Rhaze

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May 23, 2008
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This is upsetting to me...

What is the significance of PCIE 2.0? It seems like it isn't factoring in. In fact... I had no idea that the current cards were even saturating the 16x PCIE 1.0.
 

Grit

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Nov 9, 2002
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Thanks for the info and the link JPB!

This actually brings up another question: does anyone have any information about PCIe buses on the Intel chipsets that will accompany Nehalem?

Rhaze, I don't know if a single card is saturating the bus. I figured PCIe 2.0 was more futureproofing, but I have nothing technical to back that up. I also figured that with two cards (Crossfire), there might be a difference, as I remember reviews in the past that said there was some difference between a x8 and x16 for a single card.
 

Mustanggt

Diamond Member
Dec 11, 1999
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Unless you run at those high resolutions there only seems to be a diference that is big in Crysis, the lower res is pretty close to the X chipset, I run 1680x1050 is my max res so i would not see much difference in the X chipset i dont think?
 

chizow

Diamond Member
Jun 26, 2001
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Originally posted by: Rhaze
This is upsetting to me...

What is the significance of PCIE 2.0? It seems like it isn't factoring in. In fact... I had no idea that the current cards were even saturating the 16x PCIE 1.0.

Its kinda funny, I was going to post a thread on this today after reading the TweakTown article. It does appear that this generation of cards is saturating the PCIE 1.1 bus. That article clearly shows PCIE 2.0 x8/x8 being outperformed by x16/x16. PCIE 2.0 x8 is equivalent to PCIE 1.1 x16 bandwidth...so ya it looks like PCIE 1.1 x16 bandwidth is no longer enough on this generation of video cards.

I ordered an Asus P5Q-E after contemplating this yesterday. Not just for the PCIE 2.0, but also to rid myself of NV chipsets and weak FSB/Quad core overclocking.
 

nkdesistyle

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Nov 14, 2005
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P45 has only been out for less than a month, just give it sometime, there is no reason it should have any limitation with hd 4850 using x8 bandwidth on each slot, and there is no way in hell its maxing that out, it is probably driver related or the particular board they were using, I got a p5q-e myself fo 160 out the door, just becuase it burns less power and heats up less than the x38 or x48.

well if you have a 1920x1200 monitor than it should not really matter the only significant difference I saw was at the highest resolution they were testing at.

if two times 8800gtx's or even ultra's were not limited by x8 bandwidth and that was on the first gen slots, and the second gen slots should not really limit the hd 4850 by any real means. Ati actually does optimize for the new chipsets because its not their in-house chipset, so the next catalyst or the one after that should take care of that.

if you are using a monitor with 1920x1200 get the p5q-e its a great board and on an initial release bios I am running my e8400 at 4.2ghz, if you are using the 30inch monitor than by all means go with the x48.

it all depends on your needs, I did not wanna spend extra money on the x48 since the new chipsets and the native quads will be coming out at the end of the year.

Yes over P35 the P45 will be a significant difference when it comes to performance. I might crossfire once the hd 4870 comes out. I believe there was another review at bi-tech, where the p5q board was outperforming the x38 or x48 in crossfire, I am not really sure though, Asus has a good history of having their bios refined for dual card setups.

And don't just go by one review, I wish Anandtech did a comarison for the two boards and I am sur they will try to sort out if and why the P45 would perform less and they would actually go in detail about the performance issues if there are any, Tweaktown just did a crossfire X with 4 hd 4850's and where two of the cards were limited by x4 bandwidth, I would rather see them do it on a phenom system, Crossfire does not like x4 slot, I had a nightmare in a few games including my previous p35 chipset, ofourse I have sold of my hd 3870's and now I am waiting on the hd 4870 reviews.
 

nkdesistyle

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Nov 14, 2005
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in their review every game was pretty close to x48 in almost every resolution, except for crysis while running very high, it is not like that is playable even on a x48, tweaktown does not like going in depth they just write a simple conclusion, where A is faster than B, and the rest is just put aside of the conclusion.
 

bryanW1995

Lifer
May 22, 2007
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I agree, the p45 has very immature bios drivers. Once everyone gets the bioses sorted out there's no reason that 4850 won't perform the same on comparable x48 vs p45 mobos. That card definitely is NOT saturating a pci-e 2.0 x8 bandwidth.

Regarding p45 vs p35, you have the same width on the first slot (16x1 vs 8x2) but 4 times the width for the 2nd card (8x2 vs 4x1). based on previous reviews I'd say that you're looking at a 10% disadvantage in a crossfire'd p35 vs p45 going forward, though judging by that tweaktown review they are probably about equal today.
 

nkdesistyle

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Nov 14, 2005
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its not the crossfire performace that was much of an issue, well it was in some cases where it would not kick in, but the issues I had with all the games, and I tested out my hd 3870's in the P5Q-e and the difference was amazing, I had no issues in crysis, COD4, Lost planet and with the P35 board may be it was my abit board in particular, I just had a nightmare with issues across the board with numerous games I played.
 

chizow

Diamond Member
Jun 26, 2001
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Originally posted by: nkdesistyle
in their review every game was pretty close to x48 in almost every resolution, except for crysis while running very high, it is not like that is playable even on a x48, tweaktown does not like going in depth they just write a simple conclusion, where A is faster than B, and the rest is just put aside of the conclusion.

Well, I don't know, some of those differences were quite massive, especially at 2560 or with high AA. I think they're compelling enough in my case where I'm running a GTX 280 on a single PCIE 1.1 x16, but pushing more than a single 4850 would've in that benchmark over a single PCIE slot. I'm not concerned so much with the CF x8/x8 vs. x16/x16 since I'm not interested in multi-GPU, the article was interesting to me because it showed PCIE 2.0 x8 was potentially a bottleneck which is the equivalent of my PCIE 1.1 x16 slot.
 

nitromullet

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Jan 7, 2004
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I think the thing that people are forgetting here is that PCIe is a two way street. When running a single PCIe card the data is going from your motherboard to the video card, and out to your display - end of story. However, with a multi-card setup the cards are communicating with each other as well. My guess is that not all of this inter-card communication is taking place over the Crossfire bridge, and that some of it is taking place on the motherboard's PCIe bus. The way I see it, if say the actual data feed going to a single card is approx equivalent to PCIe 10x (not nearly enough to saturate a PCIe 16x slot), you could see how transferring this same data between the two cards in both directions, simultaneously on the PCIe bus could easily saturate an 8x/8x setup. I could be totally off on this, but this just makes sense to me.
 

nkdesistyle

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Nov 14, 2005
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Originally posted by: chizow
Originally posted by: nkdesistyle
in their review every game was pretty close to x48 in almost every resolution, except for crysis while running very high, it is not like that is playable even on a x48, tweaktown does not like going in depth they just write a simple conclusion, where A is faster than B, and the rest is just put aside of the conclusion.

Well, I don't know, some of those differences were quite massive, especially at 2560 or with high AA. I think they're compelling enough in my case where I'm running a GTX 280 on a single PCIE 1.1 x16, but pushing more than a single 4850 would've in that benchmark over a single PCIE slot. I'm not concerned so much with the CF x8/x8 vs. x16/x16 since I'm not interested in multi-GPU, the article was interesting to me because it showed PCIE 2.0 x8 was potentially a bottleneck which is the equivalent of my PCIE 1.1 x16 slot.

I did say that earlier, only at 2560 the difference became really noticeable, which I can beleive, but I did say earlier that at 1920x1200 the difference was not all that, even with AA on, only game that made a difference at 1920x1200 was crysis at very high, which I really don't play. I have a 26" samsung with 1920x1200 native so to me 4-5 frames don't matter. so yea with a 30" monitor at 2560, I did tell him certainly go with an x48 mobo if he had a 30" monitor, at 1920x1200 I did not see a significant enough diference in most games to pay another 100 including taxes for an x48 mobo.

LOL I always consider multigpu like I am doing right now, but I never buy them, because everytime a single new gen card is good enough to play games at high resoluiton, I was going to get the 4870 but I got the hd4850 for 150+tax and just couldn't beat that price. However if my local store gets the HD 4870 within a month I might return it for an upgrade.
 

Grit

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Nov 9, 2002
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Just to clarify my proposed setup, I currently have a P35 board and am interested in Crossfire for the 4870. My monitor is 1680x1050, but I love to play games with all the eye-candy cranked up to max (AA, AF, etc.).

Regardless, it seems that at least an upgrade to the P45 may be in order for this generation for Crossfire.

I'd prefer a single-slot solution, but I don't think I'll get the framerates I want (40+) with all the eye candy turned in future games. In some of today's games, I'm sure I'd be fine. But I don't want to re-do this when the next game I want to play comes out.

As a theory for bus saturation on Crossfire - don't PCIe cards use available system RAM to store data they may need to render future frames when it won't fit on the card? I presume THAT data must go over the PCIe bus. So, if that's correct, two cards in Crossfire may be transfering twice as much data because each card separately needs that data, correct?

 

nkdesistyle

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Nov 14, 2005
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Originally posted by: Grit
Just to clarify my proposed setup, I currently have a P35 board and am interested in Crossfire for the 4870. My monitor is 1680x1050, but I love to play games with all the eye-candy cranked up to max (AA, AF, etc.).

Regardless, it seems that at least an upgrade to the P45 may be in order for this generation for Crossfire.

I'd prefer a single-slot solution, but I don't think I'll get the framerates I want (40+) with all the eye candy turned in future games. In some of today's games, I'm sure I'd be fine. But I don't want to re-do this when the next game I want to play comes out.

As a theory for bus saturation on Crossfire - don't PCIe cards use available system RAM to store data they may need to render future frames when it won't fit on the card? I presume THAT data must go over the PCIe bus. So, if that's correct, two cards in Crossfire may be transfering twice as much data because each card separately needs that data, correct?

what kind of monitor do you have? if you have 24 or 26inch than p45 should be suffiecient enough if you got 30inch with 2560 resolution just go with an x38 or x48, as it should reduce any bottleneck. yea if you are spending 200 on a p45 board than you might as well get an x38, I got the p5q-e, best bang for your buck and great layout. and the express gate feature is really neat.
 

Sylvanas

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Jan 20, 2004
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Originally posted by: nitromullet
I think the thing that people are forgetting here is that PCIe is a two way street. When running a single PCIe card the data is going from your motherboard to the video card, and out to your display - end of story. However, with a multi-card setup the cards are communicating with each other as well. My guess is that not all of this inter-card communication is taking place over the Crossfire bridge, and that some of it is taking place on the motherboard's PCIe bus. The way I see it, if say the actual data feed going to a single card is approx equivalent to PCIe 10x (not nearly enough to saturate a PCIe 16x slot), you could see how transferring this same data between the two cards in both directions, simultaneously on the PCIe bus could easily saturate an 8x/8x setup. I could be totally off on this, but this just makes sense to me.

QFT what I was about to say.

I have been saying it for a few months now- these next gen cards need PCI-E 2.0 when in Crossfire/SLI, that goes for 4870X2 aswell I'd imagine. There is much more data going over the PCI-E Bus when you have two cards communicating via Crossfire/SLI. A good way to test this would be a increase the PCI-E frequency on the P45 which should provide additional bandwidth, which in the case of bandwidth limited cards would improve performance, I run my cards at 125mhz PCI-E just for kicks even with my Quadfire 2.0 board, but 125mhz on a P45 I'd imagine would provide quite a difference.
 

nkdesistyle

Member
Nov 14, 2005
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my p5q-e baord is not stable at all even if raise the PCI-E frequency to 105mhz, any suggestions on how what is going on.

I am running my e8400 at 4.2 with 463fsb X 9. everything is on auto except for vcore and memory voltage, tottally prime stable.
 

lopri

Elite Member
Jul 27, 2002
13,310
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P35 is especially disadvantaged because the data has to travel between NB and SB as well. And unlike AMD platform, the interconnect between NB and SB on Intel system is equivalent to PCIe x4. So everything that's tangled to SB (HDDs, NICs, USB, sound, and even legacy PS/2 or PCI stuff) ends up competing for bandwidth.

My question du jour: We know that every AMD card that supports CF has TWO connector heads. Is there a performance difference between using one CF cable and two CF cables? IIRC, these SLI/CF cables are supposedly nothing more than extra PCIe lanes.
 

bryanW1995

Lifer
May 22, 2007
11,144
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91
Originally posted by: Sylvanas
Originally posted by: nitromullet
I think the thing that people are forgetting here is that PCIe is a two way street. When running a single PCIe card the data is going from your motherboard to the video card, and out to your display - end of story. However, with a multi-card setup the cards are communicating with each other as well. My guess is that not all of this inter-card communication is taking place over the Crossfire bridge, and that some of it is taking place on the motherboard's PCIe bus. The way I see it, if say the actual data feed going to a single card is approx equivalent to PCIe 10x (not nearly enough to saturate a PCIe 16x slot), you could see how transferring this same data between the two cards in both directions, simultaneously on the PCIe bus could easily saturate an 8x/8x setup. I could be totally off on this, but this just makes sense to me.

QFT what I was about to say.

I have been saying it for a few months now- these next gen cards need PCI-E 2.0 when in Crossfire/SLI, that goes for 4870X2 aswell I'd imagine. There is much more data going over the PCI-E Bus when you have two cards communicating via Crossfire/SLI. A good way to test this would be a increase the PCI-E frequency on the P45 which should provide additional bandwidth, which in the case of bandwidth limited cards would improve performance, I run my cards at 125mhz PCI-E just for kicks even with my Quadfire 2.0 board, but 125mhz on a P45 I'd imagine would provide quite a difference.

that's so great, I never even thought of doing that on my ip35 pro if I end up going xfire on it...
 

Apocalypse23

Golden Member
Jul 14, 2003
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From my understanding, if you are going crossfire, make sure you are on a x48 board for the highest possible performance. P35s are getting old and are out of the option, P45 is the same story, as is x38.

On another note, make sure your board supports 16x and 16x bandwidth on both pci - e slots....That being said, dont even bother with crossfire :). I think a single card solution is the ultimate. My two cents.
 

Grit

Member
Nov 9, 2002
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I've given the single GPU solution some thought just for that reason. But at the same time, I want to have the expansion/room to grow this time, just in case. I kinda hate to replace my relatively new P35, esp with Nehalem coming. But I can't get any info about the Nehalem chipsets. So I'm thinking an X48 would hold me for a few more years, since the only apps I get real excited with as far as speed goes are games.