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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  • mino - Thursday, December 21, 2006 - link

    RD580 is even lower than P965 ... NF i680 and NF 590 are both power hogs.
    They are not ideal (as well as 8800GTX) for power-comparison but they are BOTH pretty hot in their respective markets.
    Reply
  • JackPack - Thursday, December 21, 2006 - link

    Where did you pull that "90%" figure out of? If a PC is idling more than 90% of the time without going into standby or hibernate, the user is an idiot.

    Hardly any PCs operate at pure idle. No real-time antivirus scan, no file indexing in the background, no email autochecking, no IE7 open with at least one Flash ad, etc.
    Reply
  • mino - Thursday, December 21, 2006 - link

    Well, how would you like Your PC to standby(not to mention hibernate) while typing or listening to MP3's ???
    At these moments (most common usage of a PC BTW) the average CPU use is 1% to 5%.

    ... ;-)
    Reply
  • mino - Thursday, December 21, 2006 - link

    Sorry fo no reading the second sentence, the first one was too crazy to continue reading back then ... So"

    Wwhat is "pure idle" ? CPU is able to go between C-states in (micro-to-mili)seconds, How fast can you type?
    AV checking? when you type? to check whether one is coding some exploit? :)
    Backgroung file-idexing? no thanks, I prefer on-MY-demand search to on OS's demand.
    Email-autocheck? done in 0.1s at 5% CPU used, once in 5 minutes...
    IE7? no, thanks, not required for Windows Update...
    Flash ad open? no, thanks, flash enabled only for reasonable sites or the ones requiring it(a few). Also, an usuall Flash is only up to 10% K8 core at 1000MHz
    etc.
    You may ask, why X2/C2D then when no background BS? Well, as of now I'm pretty happy with my Q1 install of Win2k on A1.66/512M/R9200/dualUXGA backed up by ~ 2TB NAS(with 3G P4C :). The system is more responsive than nearby mate's X2/1G with all that "necessary" bloat you mentioned.
    Me having loaded 50+ webpages and 5-10 active apps a common sight...
    Reply
  • mino - Thursday, December 21, 2006 - link

    Now I figure, maybe, maybe, the average PC has become so bloated and unmaintained as to not even be able to put CPU's to Sleep states?
    I have not seen this except outrageously malwared machives yet. However my sample size may be unrepresentative a bit too much.

    If it is so, to abandon PC and return to calculus at primary may be a good idea.
    Reply
  • JackPack - Thursday, December 21, 2006 - link

    That's not idling.

    Nice strawman, BTW.
    Reply
  • mino - Thursday, December 21, 2006 - link

    Well, wrote "90% of time" ... did not write how big the chunks of time are - they vary pretty much from tens of microseconds to tens of minutes.

    P.S. that post of mine from 10:19 was written before yours 10:13.
    Reply
  • JackPack - Thursday, December 21, 2006 - link

    ...and AMD wants to accelerate their transition to 45nm? Maybe they have a magic lamp somewhere in their Sunnyvale office.

    Seems like the increase in L2 latency might be a contingency plan for GHz or more cache, in the event Agena doesn't meet its Q3 target.
    Reply
  • Locutus465 - Thursday, December 21, 2006 - link

    I upgraded to an S939 X2 earlier this year, so I'm going to be out of the serious upgrade market for a while (might pick up a better CPU or graphics card that's about it). So personally I'm waiting for K8-L and co-processors to see how things shake out. I do have to say I had hoped better from AMD, but after 3 years of dominance I think a stumble like this is just what they need to get them back on the war path of innovation. Reply
  • peldor - Thursday, December 21, 2006 - link

    AMD's vision of coprocessors is 2009 stuff. You'll be out of the market a long time if you're waiting on that. Reply

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