When we first heard about the overclocking potential of the 4890 from AMD, we were a bit skeptical. At the same time, the numbers we were hearing were impressive and AMD doesn't have a history of talking up that sort of thing to us. There have already been some investigations around the web that do point to the 4890 as having some healthy overclocking potential, so we decided to try our hand at it and see what we could come up with.

We are testing review samples, which means that our parts may have more overclockability than off the shelf cards, but we can't attest to that at this point. What we do want to explore are the overclocking characteristics of the 4890 and how different adjustments may or may not affect performance. From what we are seeing around the web, many people are getting fairly close to the speeds we tested. Every part is different, but while clock speeds may vary, the general performance you can expect at any given point will not.

So what's so special about this AMD part that we are singling it out for overclocking anaysis? Well, the GPU has been massaged to allow for more headroom, some of which hasn't been exploited at stock clock speeds. This is the first time in a long time (or is it ever?) we are seeing multiple manufacturers bring out overclocked parts based on an AMD GPU at launch. With this as the flagship AMD GPU, we also want to see what kind of potential it has to compete with NVIDIA's top of the line GPU.

But it's more than just the chip. We also are also interested in how well the resources on the board are balanced. Core voltages and clock speeds must be selected along with framebuffer size and memory clock. These considerations must account for a target power, heat, noise and price. For high end parts, we see the emphasis on performance over other factors, but there will still be hard limits to work within.

Because of all this, balancing hardware specifications is very important. Memory bandwidth needs to be paired well with core speed in order to maximize performance. It doesn't do us as much good to have an infinitely fast core if we have slow memory that limits performance. We also aren't well served by really ridiculously fast memory if the core can't consume data quick enough. Using resources appropriately is key. And AMD did a good job balancing resources with the 4890.

Rather than just test the semi-official overclock (which is just a 50MHz core clock boost to 900MHz), we decided to test multiple core and memory overclocks (and one core + memory overclock) to better understand the performance characteristics of this beast. As expected, overclocking both core and memory saw the best results followed by only overclocking the core. Just boosting memory speed on its own didn't seem to have a significant impact on performance despite the large overclock that was possible.

So why not sell every chip at the "overclocked" speed? Well, it's all about yield. Our guess is that while the change that AMD made were certainly good enough to boost clock speed over the 4870 by a healthy margin that there were a good number of parts that couldn't be pushed up to 900MHz and AMD really didn't want to sell them as cheaper hardware. We haven't heard that endorsing the idea overclocked parts is really a policy change for AMD, so it might just be that previous layout, routing, and design choices provided for a narrower range of overclockability around the target clock frequency.

What ever the reason for it, we now have overclockable hardware from AMD. Our analysis starts with an in depth look at percent increase in performance, but if all you care about is raw performance data, we've got plenty of that in the second half. And with it comes a surprise in our conclusion we never expected.

Cranking GDDR5 All the Way Up
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  • lopri - Thursday, April 30, 2009 - link

    It's my impression that AMD cards are more responsive to clock frequencies, while NV cards are rather dependent on units/clusters. We've seen it from GTX 260 vs. GTX 280, as well as 8800 GTS vs. 8800 GTX. There were situations where GTX 280 / 8800 GTS can't come over the performance of their older brothers, even with massive overclocking. (and their clock generator don't generate clocks linearly)

    Just a thought.
    Reply
  • Depeche - Wednesday, April 29, 2009 - link

    BTW, great article but very long and time consuming xD to interesting. Keep up the great work! Reply
  • Depeche - Wednesday, April 29, 2009 - link

    Doesn't AMD make the cards a whole different way then Nvidia? Don't they have like really high clocks and memory while Nvidias is a lot lower with higher of other parts?

    Also has Nvidia made a card that's simply overclocked like the 4870/4890?
    Reply
  • SiliconDoc - Saturday, June 06, 2009 - link

    ATI has lost TWO BILLION DOLLARS SELLING THEIR GPUs ! A BILLION A YEAR EASY - YET DEREK HAS THE UNMITIGATED GAUL TO SAY THIS:
    .
    " In the meantime, NVIDIA's margins are much tighter on their larger GPUs and now their single GPU performance advantage has started to erode. It seems the wonders of the RV7xx series have yet to exhaust themselves. "
    ROFLMAO !
    THAT MIGHT MAKE SENSE IF ATI HADN'T COST AMD A BILLION PLUS A YEAR ON BARELY 2 BILLION IN SALES! ATI IS LOSING 33%.
    THEY SELL $100's OF ATI CARD, THEY LOSE $33 !
    ---
    THE TRUTH REALLY REALLY SUCKS , HUH RED ROOSTERS !
    Reply
  • SiliconDoc - Saturday, June 06, 2009 - link

    depeche: " Doesn't AMD make the cards a whole different way then Nvidia? Don't they have like really high clocks and memory while Nvidias is a lot lower with higher of other parts?

    Also has Nvidia made a card that's simply overclocked like the 4870/4890?
    "

    THE ARTICLE HERE " We absolutely must caution our readers once again that these are not off-the-shelf retail parts. These are parts sent directly to us from manufacturers and could very likely have a higher overclocking potential than retail parts. "

    LOL - WELL THAT SHOULD ANSWER YOUR QUESTION !

    cocka doodle dooooo ! cocka doodle doo ! red rooster rides again !
    Reply
  • ValiumMm - Tuesday, May 05, 2009 - link

    lol noooob Reply
  • kmmatney - Wednesday, April 29, 2009 - link

    I had an NVidia Ti4200 that overclocked well - good enough to basically double the cards value. The original Radeon LE also overcloked well, and you could unlock extra pipes. I also still have an X800GTO2 that could be Bios flashed to an X850XT. Reply
  • nubie - Wednesday, April 29, 2009 - link

    I am not sure I understand what you mean by "simply overclockable"

    Just add the coolbits registry value to the classic control panel and there are two simple sliders. It has been that way for years.

    As far as the speeds you can reach, just take care that there is enough cooling and power (voltage bumps if need be).

    I learned how to shade a resistor and take voltage measurements over at vr-zone, I think Shamino has a tutorial for it.
    Reply
  • StevoLincolnite - Wednesday, April 29, 2009 - link

    The most Overclockable card that I can remember from nVidia was the Geforce FX 5700LE it's stock core speed was 250mhz, I managed to crank my core speed on that card all the way to 640mhz on the stock Heatsink and fan, however thats not saying much as the 5700LE was basically a regular 5700 but with it's clockspeeds reduced to 5200 speeds, before that I had a Geforce 2 MX100 which was incredibly overclockable, and the TNT Vanta I had before it was as well, however I don't think I have seen a high-end part with that much overclocking margin. Reply
  • nubie - Wednesday, April 29, 2009 - link

    If you are willing to raise the voltage you can get really good overclocks.

    I had a 7900GS up to 720mhz (from 450mhz) before it couldn't take it. Backing off to 708-700 made it stable, so I settled for 650 and it has been rock-solid for 3 years.

    It all depends on the kind of cooling and power you can bring it.
    Reply

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