Hardware (cont’d)

Like the Radeon X1800 XT, the fan on the Radeon X1800 CrossFire board adjusts its RPMs based on temperature. Therefore, if things begin to get a little toasty, the card’s fan will automatically crank up the RPMs to compensate, while in 2D mode the card runs fairly quietly.

Our ears in particular are quite thankful for this feature – every time you turn on your system, the fans on the Radeon X1800 operate at full tilt. At this speed, the combination of both fans on the Radeon X1800s can get quite loud (much louder than any graphics card ATI has produced to date), nearly rivaling NVIDIA’s infamous GeForce FX 5800 Ultra in noise levels. With the fans on two X1800 cards running at full speed, the noise generated inside your system is eerily reminiscent of a Jumbo Jet at takeoff. Since we run our testbed systems outside of a case, we could literally hear the whooshing sound of the air as it passed within the plastic duct of both X1800’s, while the card’s fan has a deep, menacing tone to it.

Thankfully this only lasts for the first few seconds when you initially boot up your system, once the OS loads the ATI graphics driver kicks in, immediately sending the fan to the card’s much quieter 2D mode. Even after extended gaming sessions with both cards under full load we never saw the cards fans crank up to their full speed, overall noise was noticeable but by no means terrible. By our guesstimate we’d rank it right between the GeForce 6800 GT SLI and 6800 Ultra SLI configurations we’ve tested in the past in terms of noise generated.

Compatibility

In terms of compatibility, all Radeon X1800 XT cards you purchase at retail should be compatible with the Radeon X1800 XT CrossFire card, regardless of manufacturer. In fact, we ran many of our tests with MSI’s Radeon X1800 XT 512MB as the slave card. OVERDRIVE support is provided as well.

You can also mix and match board configurations. Say for instance, running a Radeon X1800 XT 256MB with the 512MB Radeon X1800 XT CrossFire master board. Unfortunately, you’ll lose half of the CrossFire board’s memory though. Likewise, the Radeon X1800 XL is compatible with the Radeon X1800 XT CrossFire. In fact, if you’re currently an X1800 XL user, this is the only way you’ll get CrossFire support, as ATI has no plans to produce a CrossFire board for the X1800 XL.

That’s right, ATI Radeon X1800 XL users interested in CrossFire must purchase the X1800 XT CrossFire board, which carries an MSRP of $600 – roughly $200 more than the X1800 XL card you just bought. Fortunately, the X1800 XT CrossFire board will maintain its higher clock speeds, but you will lose half of the board’s memory. Here are a few tidbits from ATI’s official CrossFire FAQ on the matter:

What happens if you pair a 16-pipeline CrossFire™ Edition
graphics card with a CrossFire™ Ready 12-pipeline graphics
card?

In this scenario both graphics cards will operate as 12-pipeline
graphics cards while in CrossFire™ mode.

What happens if the CrossFire™ Edition graphics card and the
CrossFire™ Ready graphics card have different clock speeds?

Both cards will continue to operate at their individual clock speeds;
neither card is “stepped down.” The compositing engine on the
CrossFire™ Edition card merges the resulting images independent of
the clock speed on either graphics card.

This decision has interesting ramifications for the Radeon X1800 XL in particular, as not only do you have to fork over the extra dough for an X1800 XT CrossFire only to have your 512MB CrossFire board suddenly run as a 256MB card, you’ve also got to worry about cooling if you happen to have a CrossFire motherboard that doesn’t leave extra space between the PCI-E graphics slots and places the PCI-E primary graphics slot on the bottom of the motherboard.

The CrossFire card blocks the Radeon X1800 XL airflow

Motherboards we’ve tested that are affected by this include the ASUS A8R-MVP and ATI’s RD480 reference motherboard. Since the X1800 XL gets its fresh air from the top of the card rather than the side (as you see on the Radeon X1800), in these situations the X1800 CrossFire master board obstructs the X1800 XL’s air supply and consequently, the card’s fan has to crank up to higher RPMs to compensate. As a result, our CrossFire X1800 XL setup ran louder than the X1800 XT CrossFire system, and under extended gaming sessions, we did note numerous artifacts on the screen, particularly in Quake 4 for some reason. When this would occur, we’d have to turn off the system and wait for the X1800 XL card to cool down before booting the system back up.

Considering all this, we can’t recommend CrossFire as it’s implemented today for Radeon X1800 XL users. We quizzed ATI if they’d consider adding CrossFire support via the PCI-E graphics slot (similar to what they’re doing today for X1300 and X1600 users), but we’ve yet to hear back from them. Since both PCI-E graphics slots run in x8 mode once CrossFire is enabled, this potential solution is far from ideal, but in some ways its better than the alternative. ATI’s upcoming second-generation RD580 CrossFire motherboards will provide full 16-lane PCI-E support, even when running in CrossFire mode (just like NVIDIA’s nForce4 SLI X16 chipset), but these motherboards won’t debut until next year. Perhaps at that time, it may not be a bad idea for ATI to consider providing CrossFire support via PCI-E, as right now they’re pretty adamant that they won’t be producing a dedicated CrossFire master card for the Radeon X1800 XL.

Finally, we should note that ATI hasn’t been very specific in regards to Radeon X1800 XT CrossFire’s power requirements. We used our trusty OCZ ModStream 520W PSU and didn’t run into any problems.