AMD’s Turbo: It Works

In the Pentium 4 days Intel quickly discovered that there was a ceiling in terms of how much heat you could realistically dissipate in a standard desktop PC without resorting to more exotic cooling methods. Prior to the Pentium 4, desktop PCs saw generally rising TDPs for both CPUs and GPUs with little regard to maximum power consumption. It wasn’t until we started hitting physical limits of power consumption and heat dissipation that Intel (and AMD) imposed some limits.

High end desktop CPUs now spend their days bumping up against 125 - 140W limits. While mainstream CPUs are down at 65W. Mobile CPUs are generally below 35W. These TDP limits become a problem as you scale up clock speed or core count.

In homogenous multicore CPUs you’ve got a number of identical processor cores that together have to share the maximum TDP of the processor. If a single hypothetical 4GHz processor core hits 125W, then fitting two of them into the same TDP you have to run the cores at a lower clock speed. Say 3.6GHz. Want a quad-core version? Drop the clock speed again. Six cores? Now you’re probably down to 3.2GHz.

Single Core Dual Core Quad Core Hex Core

This is fine if all of your applications are multithreaded and can use all available cores, but life is rarely so perfect. Instead you’ve got a mix of applications and workloads that’ll use anywhere from one to six cores. Browsing the web may only task one or two cores, gaming might use two or four and encoding a video can use all six. If you opt for a six core processor you get great encoding performance, but worse gaming and web browsing performance. Go for a dual core chip and you’ll run the simple things quickly, but suffer in encoding and gaming performance. There’s no winning.

With Nehalem, Intel introduced power gate transistors. Stick one of these in front of a supply voltage line to a core, turn it off and the entire core shuts off. In the past AMD and Intel only put gates in front of the clock signal going to a core (or blocks of a core), this would make sure the core remained inactive but it could still leak power - a problem that got worse with smaller transistor geometries. These power gate transistors however addressed both active and leakage power, an idle core could be almost completely shut off.

If you can take a single core out of the TDP equation, then with some extra logic (around 1M transistors on Nehalem) you can increase the frequency of the remaining cores until you run into TDP or other physical limitations. This is how Intel’s Turbo Boost technology works. Depending on how many cores are active and the amount of power they’re consuming a CPU with Intel’s Turbo Boost can run at up to some predefined frequency above its stock speed.

With Thuban, AMD introduces its own alternative called Turbo Core. The original Phenom processor had the ability to adjust the clock speed of each individual core. AMD disabled this functionality with the Phenom II to avoid some performance problems we ran into, but it’s back with Thuban.

If half (or more) of the CPU cores on a Thuban die are idle, Turbo Core does the following:

1) Decreases the clock speed of the idle cores down to as low as 800MHz.
2) Increases the voltage of all of the cores.
3) Increases the clock speed of the active cores up to 500MHz above their default clock speed.

The end result is the same as Intel’s Turbo Boost from a performance standpoint. Lightly threaded apps see a performance increase. Even heavily threaded workloads might have periods of time that are bound by the performance of a single thread - they benefit from AMD’s Turbo Core as well. In practice, Turbo Core appears to work. While I rarely saw the Phenom II X6 1090T hit 3.6GHz, I would see the occasional jump to 3.4GHz. As you can tell from the screenshot above, there's very little consistency between the cores and their operating frequencies - they all run as fast or as slow as they possibly can it seems.

AMD's Turbo Core Benefit
AMD Phenom II X6 1090T Turbo Core Disabled Turbo Core Enabled Performance Increase
x264-HD 3.03 1st Pass 71.4 fps 74.5 fps 4.3%
x264-HD 3.03 2nd Pass 29.4 fps 30.3 fps 3.1%
Left 4 Dead 117.3 fps 127.2 fps 8.4%
7-zip Compression Test 3069 KB/s 3197 KB/s 4.2%

Turbo Core generally increased performance between 2 and 10% in our standard suite of tests. Given that the max clock speed increase on a Phenom II X6 1090T is 12.5%, that’s not a bad range of performance improvement. Intel’s CPUs stand to gain a bit more (and use less power) from turbo thanks to the fact that Lynnfield, Clarkdale, et al. will physically shut off idle cores rather than just underclock them.

I have noticed a few situations where performance in a benchmark was unexpectedly low with Turbo Core enabled. This could be an artifact of independent core clocking similar to what we saw in the Phenom days, however I saw no consistent issues in my time with the chip thus far.

Introduction The Performance Summary
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  • Viditor - Thursday, May 6, 2010 - link

    There appears to be a disparity...
    In the forums, the guys who have the 1055Ts are getting 4.1GHz on 1.42v, and are doing a lot of very stable benching. It appears to be more of the rule than the exception...could you have gotten either a bad board or a bad chip?
    http://forums.anandtech.com/showthread.php?t=20698...
  • mapesdhs - Tuesday, May 11, 2010 - link


    Has anyone here bought a 1090T? How did you find it? Particularly interested in those using
    their systems for video encoding and/or animation rendering.

    Ian.
  • xXChronoXx - Sunday, June 20, 2010 - link

    I have been jumping back and forth on this issue while trying to decide if I should go with AMD or Intel for a gaming machine. Until the point where I read this article I was almost completely swayed to the side of Intel however when reading the specs of gaming performance I was somewhat surprised by just how close AMDs chip actually came on most points. I understand that the 1090T got the tar kicked out of it a lot during this comparison. However, I have to consider the fact that upgrading to a Quad Core now will almost certainly result in me having to change motherboards down the road when ( not if ) Intel decides that they no longer want to support their chipset. It makes the idea of buying a second gen chip seem like a bad choice even if it has a slightly higher performance.

    The only comparison that made me cringe was Dawn of War II and possibly Dragon Age: Origins (but only because the core i7 980x had an impressive 170fps). With the exception of Dawn of War II these framerates seem so high (and in most cases close together ) that I can't really imagine there being a noticeable difference. So my question would be this: If you're running two or more high end graphics cards in CrossfireX on the 1090T are you really going to notice any difference on a consistent basis compared to a Quad Core or are we just splitting hairs at this point?
  • lisk - Monday, July 5, 2010 - link

    I'm a chess player. I use deep rybka 4 SSE42/SSE4A based engine.
    And I find 1090T is faster than i7-930\920\870\860. And i7-965/975/980 is too expensive, so 1090T is my best choice here.
  • jsimonetti - Wednesday, July 7, 2010 - link

    Do you know if the AMD Phenom II X6 1090T will fit in my m3n-ht deluxe?
  • papalazaru - Wednesday, July 14, 2010 - link

    Price of a 1055T platform : £350
    Price of a i7 860 platform : £550
    Price of a i5 750 platform : £450

    Also there is talk of the AM3 support for the new AMD processors (Bulldozer, 8 core 28nm).

    Personally, I have no complain against my 1055T. Runs very cool and quiet (Corsair H-50), and I have good perforamnce coupled with a HD5850, copes with anything. It's a decent mid-high spec system.

    The Intel / Nvidia board is also an excellent gaming platform, especially with the arrival of the new GTX 460, that can compete directly with the HD5850 at a lower price point (which will no doubt be reduced at some point).
  • kznny - Thursday, August 19, 2010 - link

    I was think about updating my E6850 so I could play better games. Looking at your review, I clearly see the chip is not the bottleneck but the video cards are, I can go with a new SLI configuration and really rock. Saved me a lot of money - thank you!
  • pacmankiller - Monday, September 13, 2010 - link

    get your i5 or i7 to 4.5 hahahahaha put your 3d mark up the amd 1090t is the second best cpu hands down..................................................................................
  • Alaskagram - Thursday, November 11, 2010 - link

    I purchased an ASUS CG1330 with a Phenom II X6 1035T/2.6 GHZ.No where do they mention the turbo function.Is this something I can turn on or is an automatic feature?I bought this after having a Gateway 6840 which over 10 days died.When it requested that I insert the restore disk I realized that the optical drive did not have a physical eject button,consequently I could not insert the restore disc,can you say"catch 22".I bought it at cosco who does not offer on site tech help,so I had to return it,the last one of course ,and go to Best Buy.Lessons learned,support,support!
  • kenupcmac - Wednesday, December 1, 2010 - link

    should i get amd X6 1055T or intel i7 9XX for 3dmax and CAD
    i do alot of vray and lighting effect

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