Will the PCI-E 4x slot significantly hurt Crossfire performance?

Toggle sidebar Toggle sidebar
I

ihateusernames

Junior Member
Aug 31, 2008
8
0
0
Hi anandtech.

I want to build a system with an EVGA P55 LE motherboard and a Radeon HD 5850, with the intention of adding a second 5850 sometime in the future. The processor would be the i7-860, memory being the 4GB Mushkin DDR3 1600 kit.

I know the EVGA P55 LE mobo supports Crossfire, but I noticed that the second PCI-E slot is 4x, not 16x or 8x.

My question is exactly as the title says, will the PCI-E 4x slot significantly hurt the two 5850s in Crossfire's performance? How much of a performance hit would it be? Even if the first slot is 16x, would the 5850 crossfire setup run with 8x and 4x? This system would be for gaming and not for any game in particular.

Thanks, any help clearing up this confusion would be much appreciated as my Google-fu has failed me. Sorry if this should be in the motherboard forum, it seemed appropriate to place here since my primary concern is Crossfire performance.
 
crisium

crisium

Platinum Member
Aug 19, 2001
2,643
615
136
It would be such a hit that it would not be worth it; you would get similar results to if you only had one card.

8x+8x is fine and barely slower than 16x+16x. But 16x+4x is nuts and do not do it.
 
crisium

crisium

Platinum Member
Aug 19, 2001
2,643
615
136
shangshang, it depends on the motherboard. I had one that did 16x+4x and my Crossfire was the same speed as only 1 card. My new mobo does 8x+8x but I don't xfire. But tests have been done (google it) and 8x+8x is almost unnoticeable compared to 16x+16x while 16x+4x is terrible.

I'm not sure about this particular mobo, but if OP says it's 4x then avoid.
 
Last edited:
S

shangshang

Senior member
May 17, 2008
830
0
0
I haven't looked it up, but that m/b looks to have 2 x16 pci-e slots. And if my memory is correct, when you use both pci-e x16 slots, then both slots drop down to x8 speed, which is adequate for xfire. you will not lose much performance.

edit:
the x8 + x4 speed was on the older P35 chipset. On the P55 chipset, I believe it's x8 + x8
 
G

Gulzakar

Diamond Member
Oct 9, 1999
3,074
0
0
i5 and 5850 were the way to go.

In the grand scheme of things, the costs weren't that much higher. You cheaped out.
 
Hey Zeus

Hey Zeus

Banned
Dec 31, 2009
780
0
0
Gulzakar said:
i5 and 5850 were the way to go.

In the grand scheme of things, the costs weren't that much higher. You cheaped out.
Click to expand...

How exactly did i "cheap" out? Why would i want an I5? What i do want is a 32nm Quad and they're not out yet so i didn't really "Cheap" out on anything. I'll add another 5770 on friday when i get paid. :D
 
formulav8

formulav8

Diamond Member
Sep 18, 2000
7,004
522
126
AMD cpu's suck so bad that they will basically fillrate limit any videocard out there.

I get so tired of Intel fannys. AMD may not be faster than Intel, but they are not slow in the least. They can do basically everything Intels cpu's can do just not as fast.

AMD will easily push a crossfire setup. So don't listen to someones earlier fanny remark. Save some money and be happy about it :)



Jason
 
Last edited:
I

ihateusernames

Junior Member
Aug 31, 2008
8
0
0
Could we get back on topic please? Sorry I just don't want this thread to get derailed since I'm looking to buy this system relatively soon. Thanks.

Thanks for the replies so far, can anyone provide a case for the 16x and 4x slot allowing for near or same level of performance as a standard 8x 8x Crossfire setup?
 
M

mmnno

Senior member
Jan 24, 2008
381
0
0
ihateusernames said:
Could we get back on topic please? Sorry I just don't want this thread to get derailed since I'm looking to buy this system relatively soon. Thanks.

Thanks for the replies so far, can anyone provide a case for the 16x and 4x slot allowing for near or same level of performance as a standard 8x 8x Crossfire setup?
Click to expand...

Maybe yes, maybe no. Here's a test of how limiting PCI-e lanes affects the performance of a single card, but I have NO idea if that means anything for crossfire.

This old article compares old Core2 chipsets, but it's hard to draw any firm conclusions from that test as some games and settings work and some definitely do not. It seems like drivers and specific engine issues play major roles, and it's hard to say whether p55 would present the same failings as p35 and p965.

You should probably go for an 8x/8x board though. Evidence is inconclusive, so why risk it for such a paltry savings?
 
B

blanketyblank

Golden Member
Jan 23, 2007
1,149
0
0
well based on that article it looks like 4x would work pretty well since it seems a single 5870 card is still 95% effective. I've seen a similar article at Toms Hardware using a 3850 and it seems the effectiveness changes based on what game you play. In an extremely bad game the effectiveness was something like 50% but was mostly 90%+.
Any reason why you'd need to crossfire 5850s? They are pretty powerful cards even on their own.
 
formulav8

formulav8

Diamond Member
Sep 18, 2000
7,004
522
126
If the pci express slots are version 2.0 compliant it basically doubles the bandwidth. So a 4x slot should be similar bandwidth to a v1.0/1.1 8x slot and so on...

I do not think that the 4x slot will hold back any video card all that much. That review link above shows that 4x will still provide plenty of bandwidth for high end cards. Only a very minor 4%-5% difference which doesn't hardly mean a thing.

I believe that is the case anyways.... :)

Jason
 
I

ihateusernames

Junior Member
Aug 31, 2008
8
0
0
Thank you guys, that really helps me out a lot. Appreciate it.

edit for blanketyblank: That's like asking a street racer why he wants a nitrous oxide system when a stock racing engine is pretty fast. To get better performance and have more fun of course ;)

edit for mmnno: the price difference in my area is significant so that's why I'm not going for the FTW edition, as much as I'd like to.
 
Last edited:
S

soccerballtux

Lifer
Dec 30, 2004
12,553
2
76
formulav8 said:
If the pci express slots are version 2.0 compliant it basically doubles the bandwidth. So a 4x slot should be similar bandwidth to a v1.0/1.1 8x slot and so on...

I do not think that the 4x slot will hold back any video card all that much. That review link above shows that 4x will still provide plenty of bandwidth for high end cards. Only a very minor 4%-5% difference which doesn't hardly mean a thing.

I believe that is the case anyways.... :)

Jason
Click to expand...

I'm more concerned about the latency on the 2nd frames producing microstutter. We know lower speeds decrease framerate, which means it takes longer to render each frame, so OP would be viewing the 1st frame for longer than the 2nd frame.

I personally wouldn't do it, 2.0 8x/8x is about as low as I'd want to go. I wouldn't touch 16x/4x.
 
You must log in or register to reply here.

TRENDING THREADS

COMPANY
RESOURCES
FOLLOW
Top Bottom