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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  • MartinT - Thursday, December 21, 2006 - link

    AMD - Best CPU at doing nothing.

    This seems to be AMD's new mantra, no wonder given how hopelessly behind in performance and performance/Watt they are.
    Reply
  • mino - Thursday, December 21, 2006 - link

    Nicely said.

    Or better:

    CPU using the least power while doing nothing...
    Reply
  • DigitalFreak - Thursday, December 21, 2006 - link

    LOL Reply
  • Beenthere - Thursday, December 21, 2006 - link

    I doubt many PC enthusiasts place much importance on CPU power consumption. If they did Intel would never have sold any P4 chips. With Video cards drawing 200+ watts per card, a 65 nano AMD chip is a sweet piece.

    From my perspective, this is the first AMD 65 nano chips and like most process drops there is little performance gain just in lowering the nano size. AMD has a lot in the pipeline and as it arrives I suspect PC enthusiasts will be quite satisfied with both the CPU options and performance.

    It should be pretty obvious that 99.9% of the market doesn't need faster CPUs, dual cores, quad cores, etc. until we get a decent O/S that can use these CPU features and full 64-bit function. How friggin long will we have to wait for quality 64-bit software to arrive? That is something that would help PC performance significantly, yet we've been waiting two years and the software folks have delivered almost nothing.
    Reply
  • Sh0ckwave - Thursday, December 21, 2006 - link

    You're right, enthusiasts don't care about power consumption at all. We care about performance and overclocking ability.

    The average user does not need a faster CPU.

    Why doesn't Anandtech write articles for enthusiasts anymore?
    Reply
  • mino - Thursday, December 21, 2006 - link

    Also, many enthusiasts work at IT depts making decisions what architecture to go for.

    I mean, for 100s/1000s PCs deployment... An believe me, there, power IS taken into account.
    Reply
  • Final Hamlet - Thursday, December 21, 2006 - link

    Quote: I doubt many PC enthusiasts place much importance on CPU power consumption.
    If they did Intel would never have sold any P4 chips.

    That is where you are wrong. Say it after me: Million-dollar-marketing-campaign.
    Not the best product wins, but the best advertised.

    Think back to P4-times: Some average I-know-that-I-have-to-press-the-big-button-to-make-my-compie-start-Joe would enter a big (online) store like DELL where his only choice was a P4 - end of selection.
    Asked why he should buy it he would receive something like this: It has 3 REAL GHz, other manufacturers have _only_ about 2GHz. And then he would buy.


    PS I'm no AMD-fanboy. One has to clearly admit that Intel did a marvellous job with it's Core2. Only reason to buy is aforementioned power consumption in idle (my PC is idle 90% of the time) und the nice low price.

    Too strange. If you read hardware sites you could come to the conclusion that there are no single core CPUs anymore.
    Reply
  • feelingshorter - Thursday, December 21, 2006 - link

    Looking at those benchmarks, I think Intel won based on per/watt performance. AMD had lower watt usage but also lower performance. Given that a cpu can work harder, then be idle, i see per watt performance as the most important thing. I would have expected AMD to do better, but they did not come through. Reply
  • mino - Thursday, December 21, 2006 - link

    No offense, but the moment one takes into account the fact of average PC spending >90% of time at idle, well, C2D eats X2's dust.

    From energy efficiency perspective, of course.
    Reply
  • Accord99 - Thursday, December 21, 2006 - link

    Only if the C2D gets paired with a hotter chipset. The P965 motherboards tend to use 10-20W less on idle and load. Reply

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