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


View All Comments

  • balancedthinking - Thursday, June 04, 2009 - link

    Actually, you can save as much as 40W(!)idle when you underclock a 4890/4870. The important part is to underlcock the GDDR5 which automatically adjusts voltage too.">
  • 7Enigma - Friday, June 05, 2009 - link

    Anyway you could translate the 4870 portion? Babelfish is not working for me for some reason.... Reply
  • jeramhyde - Thursday, June 04, 2009 - link

    great article thanks :-) good work with the graphs and setting it out in an easy to follow way :-)

    my housemate just got a gtx275 today, so we'll be trying those overclocks tonight :-)
  • nvalhalla - Thursday, June 04, 2009 - link

    Alright, I just spent the last 10 minutes looking for a 900 shader 4980 before I realized you meant a 900MHz 4890. It's wrong in every graph. Reply
  • DerekWilson - Thursday, June 04, 2009 - link

    It's not wrong, it's just noted in a different way.

    like I say (702 core) for the GTX 275 with a 702MHz core clock, i say (900 core) for a 4890 with a 900MHz core clock.

    I'm sorry for the confusion, but it the graphs were already so crowded that I wanted to save space as much as I could.
  • nvalhalla - Thursday, June 04, 2009 - link

    no, you're not getting me. It's listed as a 4980, not a 4890. I thought it was a new card, the "NEXT TIER" if you will. The 900 I thought might be a reference to the number of SP. Once I realized you just transposed the numbers, I got the 900 was MHz. Reply
  • DerekWilson - Thursday, June 04, 2009 - link

    oooooooooooohhhhhhhhh ... okay ... that's a fun typo. I can't really do search and replace on these graphs either. I'll try and get it cleaned up as soon as I can.

    thanks for clarifying.
  • walp - Thursday, June 04, 2009 - link

    Very nice article as always! :)

    GTX275 and 4890 is really evenly matched in every different way(Price, performance, overclocking performance etc) except for the fact that 4890 can be used with the 19$ Accelero S1:">;sl=sv...

    , which makes it totally quiet and cool. Just watch those VRM-temperatures and you will be just fine!

    This is the main reason why I chosed the 4890 over GTX275, and the fact that I had a CF-compatible motherboard.

    By the way, why didnt you include the 4890 (1\1.2)GHz idle power draw? Or is it just a little type-o? :)

    Request: GTX275 SLI vs 4890 CF (And overclocking bonanza! :)))))

  • SiliconDoc - Monday, June 22, 2009 - link

    I can't help but use google and check the very first site that comes up:">
    and the GTX275 beats the TAR out of the 4890 !!!
    I guess derek has once again used some biased bench or the special from the manufacturer 4890, and then downclocked the GTX275 to boot.
  • SiliconDoc - Saturday, June 06, 2009 - link

    It's hilarious - the extravaganza overclock they do here for Nvidia can't even match the stock timings of a common EVGA.">
    core 713 derek weakness red rooster nvidia hate 703

    So what AT has done here is put the 4890 max overclocked in their other article against a low end stock gtx275, then in their extravaganza overclock gtx275 they put up a pathetic overclock that is BEATEN BY An EVGA gtx275 as it arrives !
    Worse yet, they jammed their ati 4890 maxxxxx overclocks in for comparison !
    How to be a completely biased load of crap by Derek and AT :

    max overclock your ati 4890 and put stock gtx275's against it
    weak overclock your gtx275 and put maxx overclock 4890's against it

    cocka doodle doooo ! cocka doodle dooo ! red rooster central.

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