Overclocking Extravaganza: Radeon HD 4890 To The Max
by Derek Wilson on April 29, 2009 12:01 AM EST- Posted in
- GPUs
Cranking GDDR5 All the Way Up
The first stop on our overclocking tour is in the memory subsystem. We will be increasing the memory clock frequency which reduces latency slightly and increases bandwidth significantly. The stock clock speed is 975MHz with 1ns devices (which means they are rated at 1GHz). AMD mentioned that signaling and interference (caused by the graphics hardware) are bigger problems with 1GHz GDDR5 than actually running the memory at that speed, which is why they went with the 25MHz lower clock speed.
Even with the 975MHz default clock speed, we already have a data rate of 3.9GHz. Which is pretty intense. We found in playing with ATI's built in overclocking tools (overdrive), we were able achieve stable performance at the maximum clock speed the driver allowed: 1200MHz. Doing the math gives us a massive 4.8GHz of data rate. This means, with a 256-bit wide bus, we're talking about almost 154 GB/s of bandwidth. This is more memory bandwidth than the NVIDIA GeForce GTX 280 and just a little less than the GTX 285 (which both use GDDR3 but on 512-bit busses).
So armed with 1.2GHz GDDR5, what can the 850MHz core of the Radeon HD 4890 accomplish now? Let's take a look at percent increase in performance per game when just increasing memory clock.
1680x1050 1920x1200 2560x1600
Apparently not that much more, even at 2560x1600.
Because our tests are not 100% deterministic, there is some variability in our results. Generally, this is very low, though it does vary from game to game and benchmark to benchmark. We have a hard time calling anything less than a 3% difference significant, as it could be due to fluctuations in the tests. These numbers may indicate some positive change in performance, but not one that would matter. At 2560x1600, only Call of Duty showed a performance improvement that mattered. And this is from a 225MHz overclock (just about a 23.1% increase in clock speed), which is pretty large.
There really isn't a huge need to delve into the raw numbers here, as they are just not that different. We'll hold off on that until it matters. Next up, we're going to look at increasing only the core clock speed.
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Sylvanas - Wednesday, April 29, 2009 - link
This is exactly the kind of review I like to see, overclockability is a major factor for me in purchasing new hardware. Better than the 4890 launch article, good job.SiliconDoc - Saturday, June 6, 2009 - link
Better remember this then:" 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 "
Live - Wednesday, April 29, 2009 - link
I really liked this article. Covered everything needed and was very informative.GeorgeH - Wednesday, April 29, 2009 - link
Interesting read, but I was a bit disappointed not to see the 4850x2 included in the benchmarks. The 1GB model is currently at very rough price parity with the 4890 and the 2GB model still cheaper than a 285. As such, it would've been nice to be able to more easily note the advantages of a multiple GPU card over a single GPU card cranked up to ludicrous speed.Minion4Hire - Wednesday, April 29, 2009 - link
The numbers used for the 4850 in this article correlate to those in the Multi-GPU article from February. So all you really need to do is compare the 4850 X2 results from that article to the 4890 results in this article. The two are closely matched, although I'd be willing to bet that the perceived performance and fps range is tighter and more consistent on the 4890 than the 4850 X2, as single GPU solutions usually are.Tuvok86 - Wednesday, April 29, 2009 - link
You'd better undervolt rather than underclocking.My 4890 manages a good downvolt at stock speed, resulting in low temps
kmmatney - Wednesday, April 29, 2009 - link
That is a good point. I have setup a 2D profile in ATT which undervolts the card (you can undervolt, but not overvolt with ATT) and that does help in 2D. I haven't tried undervolting at stock speed (although mine's a OC version, so it may need the full voltage).kmmatney - Wednesday, April 29, 2009 - link
I have an HD4890 and it does overclock well. But it's just too damn loud. I've been actually underclocking it for most of my games, as its fast enough to run them fine while underclocked, and it keeps the noise down. It's just not fun running it overclocked and having your game drowned out by a hairdryer. Headphones help.Veteran - Wednesday, April 29, 2009 - link
The title is a little bit stupid if you ask me, a 4890 can go way further then 1GHz on the core and 1.2GHz for the RAM. Why didn't AT go further then normal achievable clocks? The title says to the max, too bad it cannot make up the promise.Interesting read though, must have cost a tremendous amount of work.
DerekWilson - Wednesday, April 29, 2009 - link
Well ... it is to the maximum value the built-in overclocking features of the driver will let you set the card. So that's where "to the max" came from.Yes with 3rd party tools you can get higher on some hardware, but we didn't want to go into aftermarket cooling and not everyone can even make it to 1GHz ... We wanted this based somewhere in achievability.
And I'm glad it was interesting :-)