Crossfire, 4x/4x and PCI-E Connectors

[MikeHiow]

Right, now I've got my machine upgraded, I feel it time to look at improving graphical performance.

Given that 4890s seem to fetch around £80 - the best 'bang for buck' appears to stick another one in Crossfire.

It doesn't seem clear what the PCI-E configuration is in crossfire for this board (Asus P8P67) - some people claim it'll run 8x/8x and others claim 4x/4x. Is 4x really such a bad thing on a dual GPU setup that isn't exactly mindblowingly powerful?

My other question is PSU. I currently have a Corsair CX 500W and my system doesn't appear to hit over 260W at 100% load, and after reading some tests online, the peak power of a machine with 2x4890 always remains under 500W, so I think I may just get away with it (I'd expect it to be able to peak over 500W anyway, tbh?), but I only have two PCI-E connectors, which are currently both used by the current 4890. Can I use some sort of splitter, or do I need to be looking for a PSU with extra connectors?

Of course, the other option would be sell my 4890 and put that £80 or so in to fund a card for £160ish? Are there any similar/better options at this price point, either new or second hand?

 

[MeatLoaf]

Tbh im sure i saw a review where cards were tested at pci-e 2.0 sppeds ranging from x4 to x16 and there was a 5% drop in performance going from 16x to 4x

Ive had a quick look at my boards manual and if im reading it correctly it says with 2 cards they run at 8x/4x

 

[cmndr_andi]

Hi there,

Looking at this test done with two GTX 480s in a PCIe 2.0 motherboard - at 4x/4x it sure does look like performance isn't really affected that badly.

As for the PSU - I would be cautious. Each GPU has a maximum power draw of 190W, and the CPU has a maximum draw of 95W (at stock speeds). So just for the graphics cards and CPU (stock) at full load the power draw will be 475W.

However, the 12V rail of the CX 500W is only rated to 32A - which means it is only certified to deliver 408W on this rail (at 30 degrees C).

Personally, I would not trust this PSU to run your existing system and a second 4890. I would suggest one of two options

1) Sell the 4890 (expect to get ~£60 after postage) and buy a HD 5850 (this is how it compares to the 4890). Keep the same PSU.

Total Outlay: ~ £75

2) Buy a new PSU like this one. Sell the CX 500W (expect ~£25 after postage). Buy a second 4890 (~£65).

Total Outlay: ~£106

Option 1 will cost a bit less and give you the option to add a second 5850 in the future - but you will need to replace the PSU first.

Option 2 costs a bit more but will give you overall better performance in games and a good quality PSU (seasonic built, 80+ bronze) you will be able to keep for years. However, it does not give you the option to add to the graphics system further with more cards - you will need to replace the 4890s to do a further upgrade.

 

[masscrazy]

to run 2 4890s you gona need a more powerful PSU. So buying splitters and pcie connectors wont do any good.

Also running 8x/4x doesnt sound it will run both at full power.

Im in the same situation, got a motherboard with crossfire "ready" 1 at 16 the other at 4. And I have a 520w psu. And I considered 2 4890s but didnt bother as there were too many things to consider namely the PSU and motherboard capability.

You can get a 5850/6850 around £160 which has slightly better performance than the 4890. It also runs cooler and uses less power.

 

[cmndr_andi]

Im in the same situation, got a motherboard with crossfire "ready" 1 at 16 the other at 4. And I have a 520w psu. And I considered 2 4890s but didnt bother as there were too many things to consider namely the PSU and motherboard capability.

Aye, in the OP's case he is using a PCIE version 2 board, where each lane has double the bandwidth of a PCIE version 1.1 board like the P35 P5K-E WIFI.

Looking at this article - even a pair of top-end cards can run fine on dual x4/x4 PCIE v2 slots.

 

[masscrazy]

Aye, in the OP's case he is using a PCIE version 2 board, where each lane has double the bandwidth of a PCIE version 1.1 board like the P35 P5K-E WIFI.

Looking at this article - even a pair of top-end cards can run fine on dual x4/x4 PCIE v2 slots.

Touché

 

[95thrifles]

My vote goes to option one in Andi's post, if that counts for anything

 

[pecnarf]

from the post i read about 4x crossfire or 4x sli set up you need a min of 1000w psu and it need to be good brand one at that.

 

[cmndr_andi]

from the post i read about 4x crossfire or 4x sli set up you need a min of 1000w psu and it need to be good brand one at that.

It all depends on what graphics cards you put in those slots - if its two GTX 480s, then a quality 1000W would be a good idea.

However, if you are running two 4890s then a good quality 650W will be plenty.