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Radeon HD 7990 In CrossFire: The Red Wedding Of Graphics

Catching Two Tahitis Behaving Badly

This little write-up is predicated on the notion that dual-GPU cards are best-suited to four-way arrays. After all, why bother with a $1000 GeForce GTX 690 if you can snag two (faster) GeForce GTX 770s for $800? And why bother with a $1000 Radeon HD 7990 if you can find two (faster) Radeon HD 7970 GHz Edition cards for $900?

Of course, when I wrote AMD Radeon HD 7990: Eight Games And A Beastly Card For $1000, I only had access to one. Now there are enough cards to pair them up the way these things were meant to be used. Performance wasn’t even my top concern when I got my hands on an additional two Radeon HD 7990s. We already know that dual Tahiti-based configurations run into issues with dropping and truncating frames in a number of titles. AMD knows this too. The company has a driver in development intended to achieve better pacing between frames. I previewed it in the Radeon HD 7990 review, and it looks promising. Today is not the day that driver becomes available.

Rather, I wanted to know how 7990s in CrossFire coexist, both acoustically and thermally. It’s a particularly important question given the three axial fans and sink orientation AMD employs, which exhausts most of the heat out the top of the card and some down toward the motherboard (but none, really, from the I/O bracket’s cut-out exhaust).

Best-case scenario: Two-slot separation and lots of cooling

Setting Up The Experiment

The ideal test setup, then, becomes a case with enough airflow from the side to cope with two 375 W cards pushing all of their waste heat out the top, a power supply able to deliver the 1000+ W this platform pulls from the wall, and a motherboard flexible enough to give us one and two spaces between Radeon HD 7990 cards.

At launch, AMD was recommending two enclosures to support the 7990, one of which was Cooler Master’s HAF X. It’s a testament to Cooler Master that the HAF comes to highly recommended, and the company was kind enough to send one over for my experiment. In it, we installed Gigabyte’s X79S-UP5 motherboard, a Core i7-3960X, Corsair’s AX1200i power supply, and Noctua’s NH-U12S heat sink. Using an Extech 407768 sound level meter and TM200 dual-K thermometer, we tested the original press sample on its own, a retail card on its own, both retail cards together, and the press sample with a retail card for verifying the findings.  

What we discovered was that two 7990s behave quite a bit differently than one, and adding space between them only prolongs the time it takes for them to get there. While we typically see Tahiti GPUs top out in the 84-degree Celsius range, whether they’re on single-chip boards like the Radeon HD 7970 GHz Edition or dual-GPU boards like the Radeon HD 7990, three or four minutes in Unigine’s Heaven sees CrossFire’d 7990s slamming up against the processor’s 102-degree protection point. Far Cry 3 outright crashes after heating up to 98 degrees (or, if you stay in the game’s menu too long, it’ll jump up to 102 degrees as well). And 10 runs through Metro: Last Light’s benchmark has the top card’s GPUs at 97 degrees.

  • Hmmmmmm...I see. Runs too hot. You guys are in Bakersfield right? I'll tell ya what. Since we're gonna hit 100+ here anyway pretty soon, I'll shall relieve you of said cards and give you my Lasco standing upright fan. It does a way better job of cooling at the cost of acoustics. Fair deal??? XD
    Reply
  • 016ive
    2000$ for a heating system for one room!
    Reply
  • blakphoenix
    Nice and detailed read, I would wonder how they went if you had a side fan on the case (or did I miss that this test did have that)? Love how far you went with getting answers from other companies though, nice to see.
    Reply
  • Combat Wombat
    That 4 min's of gameplay would be worth burning out my new motherboard.

    7990's here I come! Not.
    Reply
  • de5_Roy
    let's see...
    the frame pacing driver that amd said would be available in june, isn't available yet.
    7990 came out over a year after 7970.
    7990(reference cooler) has problems.
    dual 7990(reference cooler) have even more problems.
    titan has high demand, enough to outsell dual gpu cards.
    nvidia has better drivers as of now.
    nvidia let gtx690 sell for a year before launching titan and gtx780 while improving drivers further (and before making fcat available outside *wink*wink*).
    oh.. i forgot about the free games. free games always make problems go away....
    .... nicely done, amd. :lol:

    i like tahiti(gcn) and it's performance. don't like the injustice amd's doing to gcn based cards. :(
    Reply
  • Twoboxer
    I wonder if a Silverstone FT02 could keep them from getting toasty :)
    Reply
  • 17seconds
    No big surprise. I wonder how many people actually own a dual 7990 setup. Can't be many, but surely they exist in the hands of owners with too much money and not enough common sense.
    Reply
  • sarinaide
    Most 7990 buids we have done have been with water cooling, not only is it better for aesthetics HS/F cooling is just not good enough for its full Tahiti cores, underwater there are no thermal issues albeit needing to spend extra on cooling. For a hardcore enthusiast its acceptable.
    Reply
  • Arls
    Liquid cooling it is....
    Reply
  • CommentariesAnd More
    This is just why I XFired 7970s for a build I made recently. The 7990 has the worst cooling you will find for a Dual GPU card. The Performance was also less by 5FPS and the issues were much less than what I read for the 7990s review. But games , are the simplest option to make up the loss according to AMD. Plus it was more expensive. Here in India the 7990s cost like 80,000 INR ( 1335 USD ) and that too after searching em for a week , thanks to no stock out here in India. Whereas I got the 7970s for under 60,000INR ( 1000 USD ) Yeah , I felt like LOL! But anyways , Games can make for the difference , but I still wont prefer it.
    Reply