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Fun With CrossFire
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Date 17th April 2007
Author Scott "Sciby" Eiby
Editor James "Agg" Rolfe
Manufacturer ATi

Crossfire lovin'

The simple fact of the computer hardware industry is that entertainment drives technological development. It's no secret that the pornography industry decided the outcome of the BetaMax vs VHS war, and it seems likely that porn again will be the deciding factor in Blu-Ray Vs HD-DVD. For computer hardware, it's primarily games that drive the constant progression of PC hardware, with a knock-on effect of driving the development of supporting software, such as OpenGL and DirectX.

In regards to the latter, DirectX 10 has just been released along with Windows Vista. nVidia has the 8800 (GTS and GTX) series of video card in the market, both of which happily support DX10. This all sounds wonderful and the next big step in gaming and shiny things for home PC's, however DirectX 9 isn't quite dead yet, thanks to Vista's cost and the limited range of DX10 video cards.

So that means there's still a bit of life in DX9 setups left, and in that vein, ATi released the X1650 chipset, aimed at the low-to-mid range market, giving people wanting to upgrade now a cheaper card that had a bit of grunt to see them through until DX10 cards were more widespread. They're also fully Crossfire capable, giving them even more longevity, at least on paper.

But the question is, is Crossfire worth the extra outlay for an extra card? Would you be better buying a single card that costs the same as the two lesser cards?

The answers to these questions of course depend on where you are with your system, and bring up more questions - do you have a Crossfire-capable motherboard and a Crossfire-ready video card installed? Are you building a new rig? Are you hoping to keep parts from your old system? Are you in the all-out pursuit of speed, or do you just want to be able to play some games, but have some longevity in your system?

Hopefully we can answer these questions for you today, as this article will focus not on the X1650 chipset, but rather on Crossfire (and indirectly, SLI) and whether it will give your system the legs it needs to remain viable with DirectX 9 until DirectX 10 gear is more readily available and, more importantly, cheaper.

Let's start with the SLI concept...

Early SLI.
Way back in the late 1990's, 3Dfx introduced the Voodoo 2 3D graphics accelerator cards, which used a small cable to connect two of the cards. This setup was named SLI, which stood for Scan Line Interleave, rather than nVidia's current SLI acronym, which stands for Scalable Link Interface.

The concept was that you could buy one Voodoo2 accelerator and when you could afford it, or whenever your games outgrew your system's abilities, you could simply buy another Voodoo2, install it and you'd have a whack more grunt. And indeed, SLI Voodoo2 rigs of the day were complete beasts, with Quake 2 being the killer app for showing off.

These cards were standard PCI cards so pretty much any system could use them, and they had a small ribbon cable that connected the cards internally. They weren't cheap ($400 per card, as my dodgy memory seems to think), and you had to have a '2d' video card as well, but they blew everything else away.

3Dfx briefly raised SLI's head again, in a way, with the Voodoo 5 5500 AGP card which featured two VSA-100 GPU's onboard. However, thanks to some bad business decisions and poor performance figures, 3Dfx and it's SLI'ing ways sank beneath the waves, so to speak.

For a long time, all of our 3D computational work was handled by just one card, and thus one GPU, usually connected via the AGP slot (and more recently, the PCIe slot), but a few years ago, nVidia and ATi both resurrected the concept of video data being processed across multiple cards. So SLI (the nVidia version) and Crossfire (ATi's version of SLI) were born. As I did all the testing with ATi video cards in a Crossfire motherboard, we'll be concentrating on that.

The concept for Crossfire is, in basic terms, the same as 3Dfx's original Voodoo2 system - you install two Crossfire-capable video cards of the same family/model, and the processing of the 3D data would be shared across the two cards - although not using the "scan line interleave" method. Regardless, you get a big boost of performance, or so the theory goes. 2D processing is still handled by the 'primary' card of the two, and everything is hunkydory.

At first, things were a little cludgy with Crossfire: you had to buy a specifically marked "Crossfire Master" card, and pair it with a standard card from the same series. They also used a large 'Y-dongle' for intercommunication between the cards.

However, this changed when ATi released the Xpress 3200 motherboard chipset - now any two standard ATi cards could be used in Crossfire mode, with the notable excepton of the X1900 series, which still requires a Master/slave/dongle setup, although the latest X1950's are being released with small ribbon cables used to link the cards inside the case.


All original content copyright James Rolfe.
All rights reserved. No reproduction allowed without written permission.
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