SLI vs Crossfire . . . I don't get it

[d_stilgar]

I have a computer running SLI right now (nothing big just two 9800GTs), and I've strayed away from crossfire because AMD just has no clue how to make it easy to understand. I was looking for chip sets that support crossfire, but it seems that chipsets that support crossfire very often also support SLI, and most products that have a compatible chipset (X58 for example) only advertise the SLI potential. I'm really confused here.

http://game.amd.com/us-en/crossfire_certified.aspx?cat=2

Am I the only one confused by this mess? I also heard there is some new tech coming out that will make it so you can use multiple cards whether ATI or Nvidia and see improvement.

[mDust]

Conceptually, they do the exact same thing.
Functionally, they are not the same. The name and architecture are the only differences.
I don't remember specifics, but back in the old days (over a year ago or so) chipsets were optimized for one or the other, basically dividing the mobo market in two. Board manufacturers have finally wizened up and started including compatibility for both in their boards effectively reuniting the 2 sides and thereby reducing the number of products they have to design...AKA cutting costs. I believe most of the newer boards allow use of either SLI or Crossfire...so it's not nearly as much of a pain as it used to be.

And the certifications are just advertisements...the boards would not be on the market if they didn't work.

[d_stilgar]

So, I'm really just looking for compatible chipsets, and pretty much every dual card motherboard, with little exception, is going to support both. Well, that makes me feel better.

[Zephik]

Is one better than the other? Like say you had an ATI card and an nVidia card that were exactly the same performance wise, would one be better than the other when paired up in either SLI or Crossfire mode?

It's funny that they don't advertise "Crossfire" instead of "SLI" since ATI cards seem to be king of the mountain at the moment. Now that I think about it, I haven't seen anyone advertise "Crossfire Compatible" in a long time. It's always just "SLI Compatible" or whatever. I wonder why that is? They should just say "Multiple Linked GPU Ready" or something like that.

[Luke122]

SLI is shorter than CROSSFIRE. :)

I maintain that BluRay beat HD-DVD for the same reason... naming.

[Kayin]

Whee, thinking this early.

All right.

SLi vs CrossFire, here's the differences.

nVidia's SLi (Scalable Link Interface) technology leverages a pair or more of video cards across the PCI-E bus through a translation hub to up graphics capability. Each card's memory is shadowed, so if you have 2 1GB cards, you have a 1 GB SLi system. SLi is a closed platform, meaning that anyone who wants to use it has to pay for a license. The number of boards that support it, however, is a lot smaller-there are maybe three current AMD boards, and a handful of Intel as well, because it won't work on any Intel chipset older than X58, and it won't work on any AMD chipset (officially.) As nVidia no longer makes AMD OR Intel chipsets, we have to expect that someone will start buying licenses for it, but don't hold your breath for AMD. Their platform beats the hell out of it anyway.

CrossFire is a direct peer-to-peer PCI-E write setup once again shadowing memory. It also brings support for asynchronous clocks, so that you can use a 4870x2 and a 4890, for example. Currently, CrossFire works on all Intel chipsets, and all AMD chipsets. All it needs is a pair of PCI-E slots and peer-to-peer writes enabled in the BIOS (HP's Blackbird, that used a Striker Extreme and still ran CrossFire too was what taught us this) to work on a system.

Both are heavily dependent on drivers, though both have default rendering modes to fall back on with no profile support. Currently, CF scales better, but SLi is still faster because of TWIMTPB optimizations.

There's more to it than that, but after that it gets into specific setups. Any more questions, just ask.

[d_stilgar]

But crossfire won't work on my current board, which is the 790i. I'm like 99% sure of that. I was just looking into last night getting all confused about everything.

[Kayin]

Yup, there is 0 CF support on that board. You're stuck with SLi.