After our in depth look at overclocking with AMD's Radeon HD 4890, many of our readers wanted to see the same thing done with NVIDIA's GTX 275. We had planned on looking at both parts from the beginning, but we knew each review would take a bit of time and effort to design and put together. Our goal has been to try and design tests that would best show the particular overclocking characteristics of the different hardware, and shoehorning all that into one review would be difficult. Different approaches are needed to evaluate overclocking with AMD and NVIDIA hardware.

For our AMD tests, we only needed to worry about memory and core clock speed. This gave us some freedom to look at clock scaling in order to better understand the hardware. On the other hand, NVIDIA divides their GPU up a bit more and has another, higher speed, clock domain for shader hardware. Throwing another variable in there has a multiplicative impact on our testing, and we had a hard time deciding what tests really mattered. If we had simply used the same approach we did with the 4890 article, we would have ended up with way too much data to easily present or meaningfully analyze.

We've kept a few key test points, as we will look at each clock at the highest speed we could achieve on its own (all other clocks set at stock speeds). We will also look at performance with all clocks set to the maximum we could hit. Beyond this, rather than looking at how performance scales over clock speed with memory and shader at their maximum and looking at how performance scales over shader speed with memory and core at their maximum, we decided it would be cleaner to look at just one more configuration. For this test, we chose core and shader speed at maximum with memory at stock.

As with the previous look at overclocking, we present our analysis based on percent increases in performance but provide the raw data as well. It's all pretty straight forward with the raw data, and we do include our highly overclocked 4890 as well as the 900MHz core clocked 4890 that can be picked up pre-overclocked from the manufacturer. For the bulk of the article, we will just be considering the impact of overclocking on the GTX 275, but our conclusion will compare AMD and NVIDIA on overclocking in this segment.

The clock speeds we were able to pull out of our GTX 275 were not to shabby as far as overclocks go. Our core clock speed could have been better, but otherwise we did pretty well. Here is what we will be looking at today:

Core: 702MHz (vs. 633MHz stock)
Memory: 1296MHz (vs. 1134MHz stock)
Shader: 1656MHz (vs. 1404MHz stock)

These are 10.9, 14.3, and 17.9 percent increases respectively. First up, we'll look at the impact of overclocking the memory, then we'll move on to core and shader. After that it's on to fully overclocked and our core/shader combined overclock.

Memory Overclocking


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  • Shadowmage - Thursday, June 04, 2009 - link

    Evenly matched? The 4890 OCed beats the GTX275 OCed in almost all benchmarks and wins considerably in every game at the resolution that I play at: 1680x1050. It also uses substantially less power and costs less than $200 (eg. ewiz deal at $160, newegg deal at $180), whereas the GTX275 still costs upwards of $220. Reply
  • walp - Thursday, June 04, 2009 - link

    I just wanted to be polite. :

    4890 @ 1\1.2 is a really nice overclock. They do mention that the GTX275 did'nt overclock that well.
    So I prefer (to be aside of the fanboyism-spectra) to call them evenly matched when talking about performance.

    Good for you that 4890 is so cheap over there, here they cost about the same as the GTX275. (280$) :/

    Powerdraw from a electrical cost-point of view is unimportant for me, since I have free electricity. (Long live the swedish King! lol..) ;)

    But it is better from a heat-point-of-view to have less power-draw of course, yeah, so 4890 is (again:slightly) better than GTX275 at load. Its the other way around for idle though. (I would sincerely call this evenly matched in powerdraw).

    I have no clue whatsoever how they compare when it comes to noise, but 4890 is really loud at load, thats for sure. ('But not anymore its not!')

  • Carfax - Thursday, June 04, 2009 - link

    Except that the GTX 275 OC had a very moderate overclock compared to the greater overclock on the HD 4890.

    I don't see how Anandtech only got 700mhz out of the core.
  • li3k - Thursday, June 04, 2009 - link


    A cursory search on google yieled the highest core overclocks obtainable on gtx 275 boards to be between 700 and 745mhz. If you can show us otherwise, please do.

    As for myself, and other hardware enthusiasts I'd imagine, the maximum potential of a card comes from its maximum overclocked performance. The fact that the gtx 275 had a "moderate" maximum overclock compared to the 4890 should not come at the cost of the 4890 in a potential comparison.

    I stand by my point.
  • Carfax - Thursday, June 04, 2009 - link

    I just googled "GTX 275 overclock" and the first article that pops up is from Guru3d which shows the GTX 275 overclocking to 743mhz.

    Tweaktown did another one and got 715mhz, but they had no clue what they were doing and left the shaders linked.

    Anyway, the point is though, if you're going to do an article on overclocking the GTX 275, why bother with a card that has such poor overclocking capability?

    Anandtech's HD 4890 OC article specifically used an HD 4890 that was capable of hitting 1ghz on the core, because not all HD 4890s are capable of attaining such a high core speed.

    Why couldn't they do the same for the GTX 275?

    This article is B.S..
  • SiliconDoc - Saturday, June 06, 2009 - link

    You can buy a GTX275 retail at 713 core - and they got theirs all the way up to 703 here ! roflmao
    Worse yet they use their 4890 numbers from their specially delivered non retail "golden ATI secret channel" - as Derek the red rooster says here in their 4890 oc extrava article ! - LOL
    " 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. "">
    a red rooster fanboy like Derek and all his little raging red roosters here love it.
  • li3k - Thursday, June 04, 2009 - link

    I have to agree...

    vote me down if you like, but the way this article is worded just reinforces the commonly held assumption that anandtech is biased towards intel/nvidia.

  • DerekWilson - Thursday, June 04, 2009 - link

    thanks for the feedback ... but I'm not touching overclocked SLI and CF ... ugh!

    I didn't include the 4890 1/1.2 in idle power because it is redundant as it doesn't affect idle power. and came in at the same idle power as the other two. I wanted to save on graph space where i could because there was so much data -- plus we already covered that in the 4890 overclocking article. Sorry if I dropped too much out.

  • walp - Thursday, June 04, 2009 - link

    Hmm, mkay.
    Was just confused by the fact that the sligthly overclocked 4890 wanted less juice than the original version in idle.
    Maybe due to better VRM\mosfet underclocking or whatever. :)

    At least do GTX275 SLI vs. 4890 CF, (and while doing that, just overclock them slightly, plz ;)
    I have my finger on the 'ordering-another-4890-button', but wont buy another until reviews 4890 CF!

  • SiliconDoc - Monday, June 22, 2009 - link

    Yes the gtx 275 wins even in overclocking... i wonder what went wrong with dereks tests...( no i don't !)

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