It’s fair to say that neither ATI or Nvidia got their dual card solutions spot on first time around. While they had great performance and a high level of stability there were various niggles like limited resolutions or card compatibility restrictions which affected the two approaches to dual card rendering. With a recent driver update Nvidia went a long way to solving many of the limitations affecting SLI systems and on the hardware side of things also released a chipset capable of two 16xPCIe graphics slots. This meant that in specific areas ATI were really lacking in features when compared to the competition, especially with only the X8 series Crossfire available to buy.

Now with the launch of Crossfire for the X1800 series ATI effectively have a second generation of Crossfire coming to market which allows them to even the playing field again. So will things be more successful for ATI this time round?

X1800 Crossfire Hardware

X1800XT Master Card

As with the X850 version of crossfire the X1800 series require the use of a master card. This card features the components required to compose the image displayed on screen when in single or dual card mode.

At first glance the card appears to be a pretty standard affair. It has a dual slot cooler as well as the passive heatsink at the rear of the card. Underneath the cooler we have a R520 core clocked at 625mhz coupled with 512mb of GDDR3 running at 1440mhz (which is slightly slower than a standard XT)

What is different is that the master card features ATI’s new "twenty" PCB (you can tell the difference as the initial cards were XX-XXX-10 and the new ones are xx-xxx-20) and therefore has six power coils for power filtering. Many of the initial cards released feature a give power coil design however these work perfectly with the 6 coil master cards.

(NOTE: The majority of X1800XTPE cards have six coils also).

The rear of the card is a pretty standard affair as you can see from the picture below.

Turning the card back over and looking even more closely allows us to see one major change to the design of the card. Just underneath the fan housing at the top and bottom of the card you can see two additional chips. The bottom chip is a Silicon Image 163B dual-link TMDS receiver chip which is partly responsible for allowing the X1800 Crossfire to process resolutions above 1600x1200 (There are actually two of these chips on the card).

Resolution being limited to 1600x1200 was the one major limitation of the X850 series crossfire due to its single link design. The new maximum resolution available by combining the 2 SI receivers (running at 165mhz and capable of receiving 2 x 1600x1200 @ 60hz) with the new more powerful composing engine is 2560x1600.

The SI Chip which you can see at the top of the card is a TDMS transmitter which is used to output the signal to any displays connected to the master card, again there are two such chips on the master.

The second major part of the Crossfire hardware sits directly beside the SI chips and is the Xilinx Spartan XC3S400 FPGA, a logic chip which handles the image composing (including blending for Super AA mode). Interestingly this chip is programmable and can be flashed should ATI decide to add features to the design in the future.

Turning to the side of the card we can see the cards bracket, this allows you to identify it as a master card immediately, whilst you have a DVI port as normal you also have the new style crossfire connector for the higher spec Crossfire cable. There is no s-video out however on the master card.

The new design Crossfire cable, as with the older X850 design, takes the output of the slave card and transfers it to the master card and is also capable of outputting to a display. Pictured below are the three connectors attached to the cable.

Currently ATI are using the existing crossfire chipset for their full range of products. The chipset codenamed RD480 is the basis for many retail motherboards such as the DFI LANParty UT RDX200 CF-DR, Asus A8R-MVP and Sapphire PURE Crossfire and all work in the same way. Just plug in your master to the lowest numbered slot and your slave to the 2nd slot and you are ready for action (This results in you using two 8x pcie slot mode rather than two 16x slots as with some SLI systems).

The new master card is also compatible with the X1800XL Radeon, when connected to one such card the Crossfire master card will deactivate 256mb of its memory (reboot required) and run quite happily in dual card mode.