Of Die Sizes, Voltages and Power

When we published our first Brisbane article, an astute reader pointed out that AMD appeared to have rather poor die scaling with the 90nm to 65nm transition. Given perfect scaling, you'd expect a 65nm shrink of a 90nm core to be approximately 52% the size of the larger core. Looking at Brisbane, AMD went from 183 mm^2 with its 90nm Windsor core down to 126 mm^2 at 65nm, making the newer core almost 69% the size of the older one. If we look at Intel, most of its die shrinks are coupled with new architectural functionality or larger caches, so it's not unusual to see scaling in the 70 - 80% range. However, with Brisbane, transistor counts remained the same according to AMD (approximately 154M) yet we still saw relatively poor scaling with die size. The table below provides some reference points for die sizes and transistor counts:

CPU Manufacturing Process Die Size Transistor Count
AMD Windsor 90nm 183 mm^2 154M
AMD Brisbane 65nm 126 mm^2 154M
Intel Smithfield 90nm 206 mm^2 230M
Intel Presler 65nm 162 mm^2 376M
Intel Prescott-2M 90nm 135 mm^2 169M
Intel Cedar Mill 65nm 81 mm^2 188M

Note that when Intel moved from 90nm to 65nm with its Smithfield to Presler transition, the 65nm core ended up being almost 79% the size of the older core. However when you take into account that transistor count went from 230M to 376M, all of the sudden the scaling looks a lot better. The bulk of that increase in transistor count was Presler's extra L2 cache, which happens to shrink quite well, so it's unfortunately not the best comparison. Looking at Prescott-2M to Cedar Mill, Intel saw very good scaling with a 40% smaller chip at 65nm (60% the size of the 90nm core).

Obviously some structures within a core will shrink better than others in terms of surface area, so perfect scaling isn't necessarily a target reality, but one of the questions we asked AMD was why the new core is seemingly so big. We couldn't get an official answer from AMD as many of the folks that would be able to get us such a thing were on vacation and unreachable, but the gist is that coupled with the fact that not everything scales well with manufacturing process, this is AMD's first 65nm chip, and AMD tends to make many improvements to its manufacturing process over time. The chip we're comparing Brisbane to was made at the pinnacle of AMD's 90nm manufacturing cycle, so it's quite possible that, with time, AMD will improve its 65nm process to the point where a smaller Brisbane would be possible. Until we can get a more technical explanation from AMD, that's the best we can report on this issue. On to number two...

We weren't impressed with the power consumption of Brisbane at all in our first review; while it was lower than its 90nm counterpart, in many cases it wasn't all that much lower. Once again this is an issue of comparing a very mature 90nm process with AMD's first 65nm chips. You see, the voltages that Brisbane will be manufactured at range from 1.250V to 1.350V, with the coolest running, highest overclocking, least power consuming chips running at 1.250V and the worst examples running at 1.350V. Both of our Brisbane samples, the 5000+ and 4800+, ran at 1.350V. Note that our 90nm 5000+ ran at 1.300V, a lower voltage than the newer 65nm core. The fact that many 65nm parts aren't at much lower voltages yet is why the highest clocked Athlon 64 X2s are still 90nm CPUs, such as the 5600+ which runs at 2.8GHz.

At some point in the future, AMD will hopefully be able to tune its manufacturing so that we will get lower voltage, lower wattage 65nm parts. This is also part of the reason why we encountered such dismal overclocking results with our 5000+. The 4800+ we tested fared no better, with our best overclock on stock cooling ending up at 2.837GHz (227 x 12.5) - not terrible for stock cooling, but not great either.

The impact of higher voltages on power consumption also applies to Intel as well. As you will see in our power comparison, in a number of cases our Core 2 Duo E6300 required even more power than the E6600 we tested last time. The reason being that our E6300 sample runs at a core voltage of 1.325V vs. 1.2625V for our E6600 sample. Just things to keep in mind as you look at the power results over the next few pages.

CPU Core Voltage of our Test Chip
AMD Athlon 64 X2 5000+ (90nm) 1.3000V
AMD Athlon 64 X2 4600+ EE (90nm) 1.2500V
AMD Athlon 64 X2 3800+ EE SFF (90nm) 1.0750V
AMD Athlon 64 X2 5000+ EE (65nm) 1.3500V
AMD Athlon 64 X2 4800+ EE (65nm) 1.3500V
Intel Core 2 Duo E6600 (65nm) 1.2625V
Intel Core 2 Duo E6400 (65nm) 1.3125V
Intel Core 2 Duo E6300 (65nm) 1.3250V
Index Brisbane Performance Issues Demystified: Higher Latencies to Blame
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  • Schugy - Thursday, December 21, 2006 - link

    Being able to sell more chips is not an argument for consumers but for AMD. Brisbane is not like Prescott - AMD has done a good job. Further development is needed but first 65nm units are running and are the basis for new architectures with increased transistor count. Reply
  • Yoshi911 - Thursday, December 21, 2006 - link

    Hey all, I know that Socket 939 is obselete now but I think It'd be awesome if they'd make a 939 65nm core.. I still have my Opteron 144 at 3.1ghz on my Lanparty board and would love to see a core I could update to before the nextgen AMD achatecture makes it out.

    Anyone know if this is a possibilty??
    Reply
  • Spoelie - Thursday, December 21, 2006 - link

    get a 165 for 150$, overclock it to at least 2.8ghz and you have fx62 like performance

    that's the best thing you will ever get on socket 939 I'm afraid, now and in the future.
    Reply
  • peldor - Thursday, December 21, 2006 - link

    Practically, it's never gonna happen. The market wouldn't be worth the effort. Reply
  • OcHungry - Thursday, December 21, 2006 - link

    I don’t understand why anyone or any review expect stellar overclocking or performance from these 65nm’s?
    Did AMD promise any? No. AMD promised a transition to 65nm and on time. That’s what we all should expect and appreciate the successful transition.
    Do you remember the first batch of Intel's 65nm Core 2’s? It was not as good as what you see today. Frankly I think AMD did much better in 65nm than Intel back then, and this first release is giving Core 2 due's matured chip a run for the money. After all the review here clearly shows AMD is on tract w/ 65nm’s performance per watt and energy consumption. Don’t forget its still K8 architecture competing w/ the latest and the greatest of Intel's.
    Reply
  • IntelUser2000 - Thursday, December 21, 2006 - link

    quote:

    Do you remember the first batch of Intel's 65nm Core 2’s? It was not as good as what you see today. Frankly I think AMD did much better in 65nm than Intel back then, and this first release is giving Core 2 due's matured chip a run for the money. After all the review here clearly shows AMD is on tract w/ 65nm’s performance per watt and energy consumption. Don’t forget its still K8 architecture competing w/ the latest and the greatest of Intel's.


    Which first batches?? The ones XS has been receiving far before the official Core 2 Duo release?? What's the OC that AT got??

    http://www.anandtech.com/cpuchipsets/showdoc.aspx?...">http://www.anandtech.com/cpuchipsets/showdoc.aspx?...

    X6800 went from 2.93GHz to 3.6GHz with default voltage. On a very good air cooler and voltage increased, it reached 4.0GHz.

    E6700: 2.667GHz to 3.4 default, 3.9 highest
    E6600: 4.0GHz highest
    X6800 stock cooler highest: 3.4GHz
    Tomshardware: X6800 to 3.46GHz
    Xbitlabs: X6800 to 3.4GHz, 3.6GHz with +voltage

    Brisbane 5000+
    2.6GHz to 2.925GHz, on stock cooler, 1.475V.

    It's not that bad for Brisbane IMO. It seems more like an architectural limitation than process or thermal limitation. Core 2 Duo still has ways to go and roadmaps sort of reflect it. Though the increase in L2 access latencies may mean it was done to increase the clock speed potential.
    Reply
  • peldor - Thursday, December 21, 2006 - link

    Going to 65nm shouldn't move you backwards in performance though. There's no excuse for that from the consumer's POV unless the price also goes down (certainly a possibility if yields are good). Reply
  • ydoucensor - Thursday, December 21, 2006 - link

    could the increase in latencies have something to do with "trusted" computing and the need for attestation? Reply
  • fitten - Thursday, December 21, 2006 - link

    Pure speculation, but the L2 latency increase may be a result of work going into the three level cache controller logic getting ready for K8L or whatever it's going to be. Reply
  • mino - Thursday, December 21, 2006 - link

    My thoughts exactly. Reply

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