P45 Chipset and Crossfire

[dajini92]

I was looking into getting this mobo:

http://www.newegg.com/Product/...x?Item=N82E16813131299

Since it's gotten good professional reviews, has great overclocking abilities, and has crossfire. However, I just realized that since it's a P45 chipset, two cards in crossfire will run at x8 each. I've heard that this won't matter, since video cards don't need anymore than x8, but I don't exactly trust that source... just looking for some confirmation here. If I decide to put two cards in to do crossfire, they will run at x8... will this mess with their performance, or do video cards not need more than x8?

 

[9nines]

X38 & X48 are faster than P45 in crossfire:

Testing article: http://www.tweaktown.com/artic...al_thoughts/index.html

 

[Heidfirst]

it's x8 PCI-E 2.0 though which is the same bandwidth as x16 PCI-E 1.x.
P45 BIOS etc. still have to mature though so I would wait a bit before assuming that X38/X48 will always be quicker in CF with current cards.

 

[dajini92]

Originally posted by: Heidfirst
it's x8 PCI-E 2.0 though which is the same bandwidth as x16 PCI-E 1.x.
P45 BIOS etc. still have to mature though so I would wait a bit before assuming that X38/X48 will always be quicker in CF with current cards.

That's the first time I've heard this... not saying you're wrong, but can anyone else verify this?

 

[Sylvanas]

Its not the bios. What one must understand is that when these modern cards are in Crossfire, there is also much increased traffic over the PCi-E bus. Lets take the example of a 4870 vs 4870 Crossfire setup. The single 4870 is probably not bottlenecked by a PCI-E 1.1 16x slot, but when placed in a Crossfire configuration there is far more data being transmitted between each GPU over the PCI-E bus via the same slot than the amount of a single 4870. So you see, a PCI-E 16x 1.1 slot is not a limiting factor in itself, it is when it is Crossfire when the bandwidth becomes too much and you require a 16x16 2.0 configuration evident on the 790fx, X38/48.

 

[Mucker]

I am perfectly happy with 4850 CF performance on my new P45 Asus P5Q-E. UT3 is super slickery smooth @ 1600 x 1200 @ 100 Hz on my 22" Mitsubishi 2070SB. Fraps shows 100 fps nearly all the time and briefly will hop down to 65 in very intense fighting. Visuals are completely stunning.

On all but the highest resolutions a P45 will suffice. If you are running very high resolutions, you obviously have the cash to spend on any hardware you want, and won't blink at the price diff between P45 and x38/48.

 

[Mustanggt]

Here is review that showes the gap between 8x8 and 16x16P45VSX48

 

[Mucker]

In that link, UT3 plays 61 fps at 2560 x 1600 on P45. Last I heard, that is a playable frame rate.

 

[DaveSimmons]

There's no real difference in UT3 at 1900x1200 but it's running at over 100 fps anyway so it isn't stressing the cards.

Crysis - 10.8 fps loss at 1280x1024 very high (32.7 vs. 21.9)
PT boats - 4.5 fps loss in min FPS at 1900 x 1200 (30.1 vs. 25.6)

The point isn't whether anyone wants to play "PT Boats," it's that real-world games at resolutions as low as 1280x1024 are losing FPS, and you'll need to cut AA/AF down to lower levels on a P45 than you would on an X48.

That's why I've ordered a P43 and 4870 instead of P45 and 4850 (to add a second later). If the 4870 ends up being too slow I'll replace it with a 4870 x2 or move up to an X48 motherboard.

 

[Mustanggt]

Why would you get a P43??

 

[DaveSimmons]

Originally posted by: Mustanggt
Why would you get a P43??

Not overclocking, only need one x16 slot, $97 vs. $130+.

Did I miss some feature that makes the P45 better for a single card and core 2 E8400 both running at stock?

 

[Gary Key]

Originally posted by: 9nines
X38 & X48 are faster than P45 in crossfire:

Testing article: http://www.tweaktown.com/artic...al_thoughts/index.html

Working on an article for Friday with CF performance on the X48/P45, the problem with that article is they did not show single card scores so you could compare percentage differences between the boards. The P45 board they used is slower clock for clock than the X48 in a single card configuration.

 

[dajini92]

So, it seems to me that since the P45 mobo I'm looking at has TWO PCIE 2.0 x 16 slots, if I run crossfire, each card will run like a single card would in a standard PCIE x16 slot (so it wouldn't be bogged down at all). Correct?

 

[DaveSimmons]

No, the specs are lying, the P45 motherboards are all x16 for one card, 2 at x8 for crossfiire.

 

[MyLeftNut]

I think what he means by "run like a single card would in a standard PCIE x16 slot" is that a pci-e 2.0 at x8 would be equivalent to a pci-e 1.1 of previous generation at x16, and yes, that would be correct.

From some reviews, it would appear that the amount of bandwidth in pci-e 1.1 x16 is adequate. However, it also does show that certain higher end cards with games which are more demanding is nearing the limit with pci-e 1.1 x16. This may suggest that, additional overhead from crossfire setups may need more than what pci-e 1.1 x16 bandwidth (or in this case pci-e 2.0 x8) is able to provide.

Or perhaps there's inefficiencies in the P45 chipset that needs to be worked out, or maybe there's some shared bandwidth going on with other things. Whatever it is, I'd like to know too and I hope someone will find out soon before I make my decision on which board to buy.

 

[Rur0ni]

I guess we'll know what's up when Gary posts the article.

 

[ShadoutDH]

Is the CF article still coming?

 

[chriskwarren]

Originally posted by: ShadoutDH
Is the CF article still coming?

I too am waiting...really looking forward to it as everyone in all the forums are quoting the tweaktown article as the definitive answer to this question.

The internets are waiting Mr. Key!

 

[Magusigne]

Buying a P45 mobo with the intention of Crossfiring is not the best idea IMHO.

If your going Crossfire x38/x48. The PCI slots might not "quite" saturate with the 4850's but they begin to show with 4870's.

No doubt the next generation of ATI cards will saturate the 8x/8x 2.0 slots.

If you want a "little" future proof, no question about the mobo choice.

I believe the benchmarks that are going to be shown soon will prove this.

Time will tell.

 

[ShadoutDH]

Would still be nice with more reviews on the issue. If HD4850 is already pushing the x8 limit, what about HD4870X2 then? Etc. Right now we only have a few tests like tweaktowns, where plenty of other reasons could explain the performance difference they saw.

 

[Mustanggt]

I ordered a X48 just to be safe, anyways with how close in price the P45s and X48s are it only makes sense, The P5Q deluxe is $209 and P5E X48 deluxe $220

 

[Magusigne]

Very good choice IMHO.

Benchmarks will back you up no doubt.

 

[Triton67]

yes, we'd like more info about this !

 

[Midaro77]

Originally posted by: Gary Key

Working on an article for Friday with CF performance on the X48/P45,...

I can't find that article on the site. Did it get delayed? Is it still coming?

I'm currently working on my first buid in forever, and P45 vs X48 for Crossfire is my last point of contention.

I need two LAN ports and 7 SATA connections, so I'm looking at either:
P45: Asus P5Q-E at $199 (in Australian dollars)
or
X48: Gigabyte GA-X48-DS5 at $305

More than a hundred bucks difference!
...and that month old Tweaktown article seems to be the only source on the whole bloody Internet!

 

[MyLeftNut]

What you could do is get the P45 and get an X2 card which will give you the same as going crossfire. On top of that, the P45 should be a better overclocker if that interests you.