Overclocking: Power, Temp, & Noise

As with the rest of Southern Islands, AMD is making sure to promote the overclockability of their cards. And why not? So far we’ve seen every 7700 and 7900 card overclock by at least 12% on stock voltage, indicating there’s a surprising amount of headroom in these cards. The fact that performance has been scaling so well with overclocking only makes overclocking even more enticing. Who doesn’t want free performance?

So how does Pircairn and the 7800 series stack up compared to the 7700 and 7900 series when it comes to overclocking? Quite well actually; it easily lives up to the standards set by AMD’s previous Southern Islands cards.

Radeon HD 7800 Series Overclocking
  AMD Radeon HD 7870 AMD Radeon HD 7850
Shipping Core Clock 1000MHz 860MHz
Shipping Memory Clock 4.8GHz 4.8GHz
Shipping Voltage 1.219v 1.213v
     
Overclock Core Clock 1150MHz 1050MHz
Overclock Memory Clock 5.4GHz 5.4GHz
Overclock Voltage 1.219v 1.213v

Overall we were able to push our 7870 from 1000MHz to 1150MHz, representing a sizable 15% core overclock. This is now the 3rd SI card we’ve hit 1125MHz or 1150MHz – the other two being the 7970 and the 7770 – so AMD’s overclocking headroom has been extremely consistent for their upper tier cards.

As for memory overclocking, we hit 5.4GHz on both cards before general performance started to plateau, representing a 12.5% memory overclock. Considering that both cards use the same RAM on the same PCB, and the performance limitation is the memory bus itself, this is consistent with what we would have expected. With that said, we are a bit surprised that we got so far over 5GHz on 2Gb GDDR5 memory chips only rated for 5GHz in the first place; it indicates that Hynix’s GDDR5 production very mature.

With that said, because of the unique and non-retail nature of the 7850 AMD supplied us, the 7850 overclocking results should be considered low-confidence. The retail 7850 cards will be using simpler and no doubt cheaper coolers, PCBs, and VRMs; all of these can reduce the amount of overclocking headroom a card has. It’s by no means impossible that a 7850 could hit 1050MHz/5.4GHz, but it’s far more likely on a 7870 PCB than it is on a 7850 PCB.

Anyhow we’ll take a look at gaming performance in a moment, but in the meantime let’s take a look at what our overclocks do to power, temperature, and noise.

Even without a voltage increase overclocking does cause power consumption to go up, but not by a great deal. Under Metro the total difference is roughly 21W for the 7850 and 25W for the 7870, at least some of which can be traced back to the increased load on the CPU. Whereas on OCCT there’s a difference of nearly 40W on both cards, thanks to the increased PowerTune limits we’re using to avoid any kind of throttling when overclocked. All things considered with our overclocks power consumption for the 7850 approaches that of the 7870 and the 7870 approaches the GTX 560 Ti, which as we’ll see is a fairly small power consumption increase for the performance increase we’re getting.

Of course when power consumption goes up so does temperature. For both cards under Metro and for the 7870 under OCCT this amounts to a 5C increase, while the 7850 rises 8C under Metro. However as with our regular temperature readings we would not suggest putting too much consideration into the 7950 numbers since it’s using a non-retail design.

AMD’s conservative fan profiles mean that what are already somewhat loud cards get a bit louder, but in spite of what the earlier power draw differences would imply the increase in noise is rather limited. Paying particular attention to Metro 2033 here, the 7870 is just shy of 3dB louder at 51.9dB, while the 7850 increases by 2.7dB to 51.5dB. OCCT does end up being worse at 2.8dB and 3.7dB louder respectively, but keep in mind this is our pathological case with a much higher PowerTune limit.

Power, Temperature, & Noise Overclocking: Gaming & Compute Performance
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  • Kiste - Monday, March 5, 2012 - link

    So, how many people do you know who would spend a few hundred bucks for a performance "sidegrade" that saves them a few bucks per year on their energy bill?

    Price/performance is still the relevant metric for most people, with everything else being secondary. Not unimportant, but secondary. Noise can also be addressed on cards with high power draw by buying a card with a custom cooler or using a 3rd party cooler.
  • Kaboose - Monday, March 5, 2012 - link

    Some people are just entering the market, some people are coming from 3+ generations ago, some people are looking for HTPC's that can game and need low power and low temp cards that provide solid performance. It isn't a sidegrade for someone who is coming from integrated graphics or maybe a 7800GT etc. It is easy to think that everyone who buys these types of GPU's are knowledgeable and already have high performing GPU's. But that just isn't the case a lot of the time. If you have a high end 5xxx or a mid-high range 6xxx GPU already then there is no reason to upgrade, frankly with the 68xx series AMD isn't looking to grab that market.
  • Kiste - Monday, March 5, 2012 - link

    If you're looking for great price/performance, there are plenty of cards that offer more bang for your bucks.

    If you're looking for raw performance, you look elsewhere, too.

    Though I'll happily concede that the 7850/7870 are great absolutely fabulous for everyone who is building a "HTPC that can game".
  • medi01 - Monday, March 5, 2012 - link

    And exactly where do you look for raw performance, pretty please? Maybe at nVidia 570, that costs 80$, consumes more energy yet is outperformed in most tests by 7850?
  • Kiste - Monday, March 5, 2012 - link

    Where would you look for raw performance? How about the 79xx line?

    And what the hell are you talking about anyway? The 7850 does not "outperform" the 570 in most tests, unless you're again back at comparing an overclocked card to a non-overclocked card. Most 570 cards can do a 15-20% OC easily, btw.

    Hell, I bought my GTX570 about 12 months ago for €289. And I'm supposed to be blown away by something like the 7870 in 2012?

    The GTX570 became available about 14 months ago. It took AMD 14 frigging month to come up with a card like the 7870 that is 9% faster on average at the same price point?

    Gee, what a marvel of technology.
  • krumme - Monday, March 5, 2012 - link

    570 is 250% larger and 9% slower
    Its a giant leap
    talk about marvel of technology
    Your card is tech from stone age compared to a 7870.
    Old tech is old
  • SlyNine - Monday, March 5, 2012 - link

    I'm running a 5870 which is basically 75% the performance of a 7970, and I paid 379 for the 5870. Which is also 75% of the cost of a 7970. The price of a 7970 is basically the exact same price structure as the 2 1/2 year old 5870, So we are stuck where we were in 2009, yay.

    Yea we are sure moving forward...
  • morfinx - Monday, March 5, 2012 - link

    75% performance of 7970 would mean that it's 33% faster than a 5870. And that's just not accurate. I have a 5870 as well, so I was paying a lot of attention on how much faster the 7970 is in various reviews. Everything I've read indicates that it's anywhere from 70-110% faster at 2560x1600 resolution (I run 3600x1920, so likely even even more of a difference). That's not even even considering the massive overclocking headroom of the 7970 vs barely any OC headroom of the 5870. Overclocked, a 7970 is easily twice as fast as a 5870.
  • RaistlinZ - Monday, March 5, 2012 - link

    This is true. I came from a 5870 to a 7970 and at 2560x1600 the 7970 is easily twice as fast.

    And that's even before overclocking. My 5870 could barely overclock for crap, whereas my 7970 overclocks 27% on core and 18% on memory.
  • SlyNine - Thursday, March 8, 2012 - link

    Not according to Anandtechs benchmarks.

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