SLI & Crossfire

[Emoz93]

I'm curious. What are differences between SLI and Crossfire? Apart from the fact that the former is Nvidia's technology and the latter is AMD's technology.

[Gilly]

http://www.build-gaming-computers.com/nvidia-sli.html

http://www.build-gaming-computers.com/ati-crossfire.html

[Armenius]

Beyond that, SLI requires a hardware bridge to enable communication between cards while Crossfire does not.

[Emoz93]

My motherboard has two PCIe x16 (not v2.0). According to the manual, it supports CrossFire but didn't mention SLI?

[Paradigm Shifter]

What's the mobo? If it's an Intel chipset, Intel licensed CrossFire for their chipsets from AMD (or ATi as it was at the time) but didn't license SLI from nVidia. This changed with the X58 (Core i7) chipset, but was dependent on the mobo manufacturers paying royalties to nVidia. If they didn't (and therefore made the board cheaper) then it couldn't do SLI.

With two 16x PCI-E slots, there is no physical reason why SLI won't work. There are even software hacks to enable SLI on motherboards that don't officially support it. But it's very sensitive to drivers, and has been dogged with a slew of virus false-positives over the last few releases IIRC.

[GenericBeing]

I have been using SLI hack for almost a year now. Yeah there has been some issues especially after Nvidia put a timebomb in their drivers - causing black screen after 3-5 minutes after a game was launched, drivers has stopped responding and had to be reset error (malware anyone?). But that has got fixed after some months.

Currently using SLI hack v1.0 with 266.58 drivers.

Also I recall I didn't need an SLI bridge first time when I setup the system. But without SLI bridge you have to go through the PCI-E lanes so more prone to bottlenecking. Did this change with recent drivers?

Also you may need to update BIOS for certain chipsets, just google it if you are interested.

[Armenius]

There is more noticeable page flipping when one GPU displays its frame after the other without the bridge, and the performance without it is about 1/3 of SLI with the bridge (the only reason I know this is because when I first put my computer together I didn't know what that extra ribbon that came with my MoBo was until I read about it later...). SFR (split-frame rendering) cannot sync up correctly without the bridge, but there are not many games that use this form of SLI. I have a feeling that there could be more issues when not using the bridge under tri-SLI situations.

[Emoz93]

What's the mobo?

Intel P35

[Paradigm Shifter]

That'll be 16x on one slot and 4x on the other. Which is a nasty, nasty bottleneck.

[Emoz93]

I was always confused. According to my mobo's manual: "2 x PCIe x16 (blue @x16 mode, black @x4 or x1 mode)". How can it be an x16 slot when it is running at only max. x4 mode?

After a bit of searching through the net, I found that P45 only supports one PCIe 2.0 x16 & one PCIe 2.0 x8, so in CrossFire mode both cards will run at x8. X38 & X48 chipset has two PCIe 2.0 x16, enabling the cards running at full x16 speed.

Conclusion? Save more $$$ for a new mobo if I ever want to do CrossFire.

[Paradigm Shifter]

The slot physically is a 16x slot. But electrically it's on a 4x slot. PCI-E is great as it doesn't matter whether a device is a 1x, 4x, 8x or 16x device... if it'll physically fit in the slot, it'll work. (In theory).

[suiken_2mieu]

The slot physically is a 16x slot. But electrically it's on a 4x slot. PCI-E is great as it doesn't matter whether a device is a 1x, 4x, 8x or 16x device... if it'll physically fit in the slot, it'll work. (In theory).

Haha, I put a GFX card in a 1x slot and it worked. I have to melt the back off of it, but yeah it worked (amazingly). Performance wasn't that bad either.

[Paradigm Shifter]

Haha, I put a GFX card in a 1x slot and it worked. I have to melt the back off of it, but yeah it worked (amazingly). Performance wasn't that bad either.

Yeah, I know it will... that's why some mobos have open-ended PCI-E slots... :)