45nm and Low Power Consumption

Built on a 45nm process, Phenom II is finally using the same feature size as Intel’s processors. Intel’s 45nm caches are a bit smaller than AMD’s, but it’s no longer a 65nm vs. 45nm playing field - things are much more even. However, AMD and Intel’s approaches to 45nm differ considerably.

Circuits are placed on silicon wafers through the use of photolithography. Light is shone on a mask, and the light then makes it through the mask and etches the circuits on the silicon wafer. The wavelength of light used determines the minimum feature size of the circuits on the wafer. By itself, 193nm wavelength deep ultra-violet light is only useful for circuit feature sizes down to 50nm. To reach 45nm and beyond you need to do a little more.

AMD uses immersion lithography, which places a liquid between the source of the light and the wafer itself. The liquid increases the resolution at which the light can focus, allowing for smaller than 50nm feature sizes with currently available tools. Immersion lithography isn’t a performance enhancing feature; it’s simply one that makes it possible for AMD to manufacture at 45nm.

Intel claims that immersion lithography isn't necessary at 45nm and doesn't use it. Intel uses a technique known as double patterning but only on the gate layer of the chip. Intel’s approach requires higher mask costs but can result in a high yield 45nm chip without the use of immersion lithography. AMD’s approach should be more cost effective initially since you have to create fewer masks, but Intel’s scale of 45nm production should help offset that. For what it's worth, the double patterning has been in use since Intel's 65nm process.

Remember Intel’s high-k + metal gate transistor announcement? That’s still a feature advantage that Intel holds at 45nm. The new transistors make sure that current doesn’t flow when it’s not supposed to, reducing power consumption.

The two processes, despite both being 45nm, are different enough that they aren't the same despite having similar feature size - but comparing manufacturing processes is beyond the scope of this article.

A Power Efficient Phenom?

When Phenom first hit, not only was it underperforming, but it also drew far too much power. Combine that with a CnQ mode that robbed users of performance and you ended up with a CPU that was hardly power efficient. Just like the cache deficiency, Phenom II fixes this.

With Core i7, Intel developed power gate transistors that can completely shut off an individual core that’s not in use. Intel’s cache hierarchy is inclusive so any data stored within a core’s L1 and L2 caches is already duplicated in the L3 cache; if a core isn’t in use it can be shut down and there’s no need to wake it back up until it’s needed again.

Remember, Phenom II isn’t a complete redesign, so AMD couldn’t work on a similar technology. Despite that, idle power in Phenom II is greatly improved. When a single core is idle, the contents of its L1 and L2 can be flushed out to L3, allowing the processor to halt the clocks to that core - thus reducing power. The core will still consume leakage power, but it’ll be far less than if it were running at the lowest p-state. Intel introduced something similar back in the Conroe days, except data from L1 was pushed out to L2 before the core was powered down since there was no L3. Nehalem still has the ultimate in idle power thanks to Intel’s power gate transistors, but as you can see below Phenom II’s idle numbers are quite impressive.

Processor Idle Power Load Power
AMD Phenom II X4 940 (3.0GHz) 109.6W 189.7W
AMD Phenom 9950 BE (2.6GHz) 124.2W 210W
AMD Phenom X3 8750 (2.4GHz) 127.5W 210W
AMD Athlon X2 6400 (3.2GHz) 101W 195W
Intel Core i7-965 (3.2GHz) 99W 199W
Intel Core i7-920 (2.66GHz) 95W 168W
Intel Core 2 Extreme QX9770 (3.2GHz) 135W 219W
Intel Core 2 Quad Q9400 (2.66GHz) 126W 174W
Intel Core 2 Quad Q8200 (2.33GHz) 134W 168W
Intel Core 2 Duo E8600 (3.33GHz) 124W 157W

Note that while Penryn’s idle power isn’t nearly as low as Phenom II, this has more to do with Penryn’s lowest operating frequency. Phenom II’s minimum p-state is only 800MHz, compared to 2.0GHz on Penryn. Load power is also impressive, not quite Nehalem impressive but definitely competitive with Penryn at least.

In load power, Penryn still has the advantage. The Q9400 draws 174W compared to 190W for the Phenom II X4 940. The Core i7 is still the most power efficient of the two, as the i7-920 draws less power and is faster than the Phenom II X4 940.

Finally, Cool 'n' Quiet You Can Use Socket-AM2, AM2+ and AM3: Backwards Compatibility
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  • Spoelie - Thursday, January 8, 2009 - link

    Only one little gripe: why was a mid-range motherboard used for the phenom while the intel processors got enthusiast versions?

    there IS a difference apparently: http://www.legitreviews.com/article/795/5/">http://www.legitreviews.com/article/795/5/

    Not that it would change the conclusions.
    Reply
  • melgross - Thursday, January 8, 2009 - link

    "Not that it would change the conclusions. "

    You answered your question yourself.
    Reply
  • duploxxx - Thursday, January 8, 2009 - link

    Nice review, always my firts site to read for a review. A bit basic on oc potential but you hint there is more to come, lets hope we don't have to wait another month like we had to wait for the 790GX board reviews.

    I don't see why AMD launched the unicore @1.8ghz.

    You are stating that it is because of yields, might be but shanghai launched @2.0-2.2. Phenom2 would scale a lot better performance wise against penryn with a 2,2GHZ NB speed. for sure on the BE part that is a real advantage against the q9400-Q9550

    Is this to give the am3+ an additional performance gain when launched? Retail chips hit NB speeds of 2,4-2,6 easy, they also showed up to 3.5-3.6ghz oc on stock vcore, your oc gain was real low, perhaps you show in future oc review what phenom can actually do.

    no overview of total system power consumption idle and load?
    Reply
  • ssj4Gogeta - Thursday, January 8, 2009 - link

    Since most of the people have Intel now, it'll take them only a processor upgrade if they decided to buy a better Intel processor. But if they choose to switch to AMD, they'll have to buy the mobo as well.

    So for *most* people, getting a Q9400 (or Q9550 if the prices drop) will cost around $270, while getting a Phenom II 940 will cost around $470. And since this is the case for the majority, I don't see Phenom II being price competitive at all.
    Reply
  • RadnorHarkonnen - Thursday, January 8, 2009 - link

    There are more people with AM2+ Motherboards than you can think of.
    They may not spew they writings on the forums or comment actively saying "I'm upgrading!!!".

    Units shipped, i would say you r are really short sighted. And the AMD2/AMD3 compatibility is great.
    Reply
  • KikassAssassin - Thursday, January 8, 2009 - link

    Yeah, for people building new systems right now who don't want to spend the money on an expensive i7 mobo and DDR3, the Phenom II looks really nice. Intel probably isn't going to make any more LGA775 CPUs, whereas an AM2+ system might have more room for future upgrades with AM3 being backwards compatible. Reply
  • melgross - Thursday, January 8, 2009 - link

    But if you do go the i7 route now, you won't have to upgrade for a longer time than if you go with Phenom 1. Overall costs over time will still be lower. Reply
  • melgross - Thursday, January 8, 2009 - link

    Oops! meant Phenom 11, or course. Anyway, the higher performance vs the price is worthwhile for many people. Reply
  • plonk420 - Thursday, January 8, 2009 - link

    ask Dark Shikari of x264 fame .. i'm sure he could tell you an approximation of Phenom's L3 cache latency... and possibly Phenom II latency soon. Reply
  • hameed - Thursday, January 8, 2009 - link

    In the first table here http://www.anandtech.com/cpuchipsets/showdoc.aspx?...">http://www.anandtech.com/cpuchipsets/showdoc.aspx?... the percentages are hard to understand since they need to be flipped (i7 is before Quad) and btw in Cinebench the Quad advantage is 12.8% not 4.8% and the CS4 percentages are also not accurate. Reply

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