Why Bother with Three Cores?

The table below shows the problem with four cores:

SYSMark 2007 Overall E-Learning Video Creation Productivity 3D
Intel Celeron 420 (1 core, 512KB, 1.6GHz) 55 52 55 54 58
Intel Celeron E1200 (2 cores, 512KB, 1.6GHz) 76 68 91 70 78
% Increase from 1 to 2 cores 38% 31% 65% 30% 34%
Intel Core 2 Duo E6750 (2 cores, 4MB, 2.66GHz) 138 147 141 120 145
Intel Core 2 Quad Q6700 (4 cores, 8MB, 2.66GHz) 150 145 177 121 163
% Increase from 2 to 4 cores 8.7% 0% 26% 1% 12%

When going from one to two cores, overall system performance increases a decent amount. SYSMark encapsulates a wide variety of applications and usage models and overall performance increases by close to 40%. Obviously areas like video encoding (represented in the Video Creation tests) see the biggest gain, but all aspects of performance increase tremendously. Making the argument for two cores these days isn't a difficult one, most desktop applications can at least take some advantage of two cores.

Looking at the move from two to four cores however reveals much worse scaling. In our 1-to-2 core comparison cache size didn't increase, so the theoretical scaling could actually be even higher but in the 2-to-4 core comparison the total L2 doubles since Intel's quad-core processors are simply two dual-core die on a single package. Despite the increase in cache size however, scaling is quite poor. Overall performance goes up 8.7% percent and the E-Learning/Productivity tests see no gains at all. Once again the biggest gains come from the Video Creation tests, followed by the 3D suite.

For the vast majority of systems, four cores just aren't necessary. There are some applications that do scale very well between 2 and 4 cores, but the overall landscape is much like what we saw with dual-core CPUs circa 2005, the time for quad just isn't now. Intel's CPU shipments also reflect that both the need and demand for quad-core CPUs just isn't very high:

Currently, less than 10% of Intel's consumer desktop CPU shipments are quad-core and that number won't grow much beyond 10% by the end of 2008. But just like the early days of dual-core, we'll see a steady ramp up continuing in the years ahead.

The point here isn't that quad-core processors aren't necessary, rather they aren't quite in their prime as far as demand goes. With such a small portion of the market purchasing quad-core CPUs, the ISVs aren't exactly jumping at the opportunity to make sure all applications scale well from 2-to-4 cores. Some inherently won't scale while others may with additional effort, which requires a large install base and once more we find ourselves in the midst of an overused analogy involving chickens and eggs.

For Intel, a slow adoption of quad-core CPUs isn't much of a problem. It's just as easy to make a Core 2 Quad as it is to make a Core 2 Duo, the former simply has two dual-core die on the package instead of one. For AMD however, things are a lot more complicated.

One often cited reason for Phenom's late arrival was its "native" quad-core design. Due to its on-die memory controller/north bridge, AMD could not simply take two Athlon X2 die and individually place them on the same package; all four cores would have to be behind the memory interface, meaning that all four cores would have to be on the same die.

Number of Cores Manufacturing Process Transistor Count Die Size
AMD Phenom X4 4 65nm 450M 285 mm^2
AMD Phenom X3 3 65nm 450M 285 mm^2
AMD Athlon X2 2 90nm 243M 219 mm^2
AMD Athlon X2 2 65nm 221M 118 mm^2
Intel Core 2 Quad 4 65nm 582M 286 mm^2
Intel Core 2 Duo 2 65nm 291M 143 mm^2
Intel Core 2 Quad 4 45nm 820M 214 mm^2
Intel Core 2 Duo 2 45nm 410M 107 mm^2

Looking at the die size column you can see an issue with AMD's current processor lineup. AMD likes building the 65nm Athlon X2s, they are nice and small at 118 mm^2 per die and it can make a lot of them on a single 65nm wafer. The Athlon X2 6400+ is still built on a 90nm process and its die, by comparison, is huge; AMD doesn't like making these chips very much (update: AMD has actually ceased production of 90nm X2s altogether).

Then we have Phenom. At 285 mm^2, Phenom is huge and AMD can't make that many per wafer, plus with such a large die the yield is lower than on a smaller chip. The triple-core Phenom X3 gives AMD something to do with those quad-core die that have a single defective core, rather than throwing the entire chip away it can now be repackaged and sold as a triple-core processors.

The other problem here is that there is no dual-core Phenom, so AMD must battle Intel's 45nm dual-core processors with its very old 65nm Athlon X2s. The Phenom X3 is designed to help alleviate the burden of those poor K8s by competing with Intel's dual-core in the sub-$200 space. It's a great marketing story too: you can get three cores from AMD for the price of two from Intel.

It's more likely than not that AMD's yields aren't bad enough to have too many quad-core Phenom processors with two defective cores, which is probably why we don't see a 285 mm^2 Phenom X2.

AMD has no plans to make a separate triple-core die, simply because it would require quite a bit of engineering resources and the need for triple-core CPUs diminishes over time as quad-core adoption increases. Right now AMD is focused on bringing its 45nm Phenom processors to market and those are occupying all of AMD's availability engineering resources. Should triple-core prove to be a worthwhile addition to the lineup, AMD could always work on designing a tri-core die but for now it will fulfill its role as a stopgap solution.

Index A New CPU & Intel's Biggest Problem
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  • Locutus465 - Wednesday, April 23, 2008 - link

    I just upgraded my system to the following last night (running vista ultimate ed. 64bit).

    AMD Phenom 9850be (at stock speed for now, with packaged heatsink).
    4GB OCz DDR2 800 memory (at stock speed)
    ASUS M3A32-MVP Deluxe / WiFi-AP AMD 790FX
    DIAMOND Viper Radeon HD 3870
    Soundblaster x-fi Fatal1ty

    The rest of my system stayed the same, primary hdd = WD Caviar SATA 7200RPM, secondary = Segate SATA 7200RPM, page file running off of secondary disc rather than system disc etc.

    I can tell you right now that the all AMD platform is very strong. As my primary display I have a 19" LCD running 1280x1024 and I run all games with all graphics options set to max and never get below 70FPS on any game I know how to pull the FPS for. I'm able to run crysis very smoothly at the same resolution with medium graphics settings, I have not yet tried cranking things up though. Additionally I've had to take some of my work home which delt with converting a 3GB pipe delimited file in to several smaller files then converting those into valid CSV files (using excel), on my new system this process was very quick. For your reference below is a list of every game I've tried on my system, they ALL play silky smooth.

    Doom 3
    Quake 4
    Age of Empires III
    F.E.A.R
    Oblivion
    Half Life 2
    Half Life 2 EP1
    WoW
    *Crysis

    *only game I don't have graphics/audio settings fully maxed on.

    Since upgrading I've also taken to gaming on my 720P Toshi DLP using the DVI to HDMI converter packaged with my video card and audio running through my AVR via multi-channel analog inputs. All I have to say is damn is that fun!!!
    Reply
  • Ensoph42 - Wednesday, April 23, 2008 - link

    I don't understand why every review I've seen for the Phenoms use DDR2-800. I thought one of the perks was that you were supposed to use DDR2-1066 to get max performance. Someone explain this to me. Reply
  • niva - Wednesday, April 23, 2008 - link

    I have a phenom 9600 with 8Gb of RAM, I had major issues getting the RAM to 1066 and remaining stable, simply stayed with 800 for stability reasons. Then again, I don't play games much so I'm not concerned about squeezing out an extra 1-5% performance for the sake of stability.

    Of course I didn't play with this too much, maybe I was doing something wrong but I've not found a good guide saying exactly what I need to set for the system to remain stable.
    Reply
  • Ensoph42 - Wednesday, April 23, 2008 - link

    I hear you. Although is it that your mem is rated at 800 and wont OC to 1066? Or rated for 1066 but just isn't stable period at that speed?

    However the GIGABYTE GA-MA78GM-S2H, that is used in the review, has a memory standard of DDR2-1066. One of the selling points of the Phenom, I believed, was the memory controller supported DDR2-1066.

    I found this link here that takes a look at performance differences. I havent given it a close read since it's late, and seems limited but:

    http://www.digit-life.com/articles3/mainboard/ddr2...">http://www.digit-life.com/articles3/mainboard/ddr2...



    Reply
  • perzy - Wednesday, April 23, 2008 - link

    Well unless the software is as well written as Unreal engine 3 (Tim Sweeney is a god),in 95% of the programs avrege Joe use (including windows itself) there is very little advantage even going from singlecore to dualcore!
    Which brings me to my question: Whats really going on with the 'Heat wall' 'Frequenzy wall' or whatever you call it that Intel hit so hard in 2004(-ish) ? (remember the throttling superhot 3.8 GHz P4's ?)
    What all users really need is higher frequenzy! Why arn't we getting it?
    Reply
  • Clauzii - Wednesday, April 23, 2008 - link

    The frequency wall can be considered like cooking the electrons off of the DIE-surface, which is not so good. High frequency=High heat. Now Youre thinking, "But IBM got 6GHz?". It's a different design philosophy: Simpler pipeline, faster frequency.

    Until ALL programs/OSes support multi-threaded programs, we are bound to single-threaded OR the pseudo Hyperthreading which can do SOME multithreading, depending on the Code & Data used.

    If I've used a 8 GHz machine to write this on, I would still only be able to see the cursor rate one pr. sec.

    What I think we need are (even more!) intelligent CPUs (GPUs). If a CPU or GPU knew approx. what kind of performance and usage of power a program needs, a more sofisticated power scheme could be possible??

    Until then, All I know is that evolution goes forward. Not always fast, but forward :)
    Reply
  • Nehemoth - Wednesday, April 23, 2008 - link

    ...(or give up 200MHz and get a quad-core X3 9550 at the same price)...

    Should be Quad-Core X4 no X3
    Reply
  • MrBlastman - Wednesday, April 23, 2008 - link

    I'd like to see them include the X2 6400 in the benchmarks as well. I see that they might be trying to get the pricing in line, but for an AMD user looking to upgrade, all I really am considering right now is a 6400, X3 or X4, nothing else.

    The UT 3 benchmarks shed some hope for the Phenoms as they show with a properly coded game, the X4's can remain competitive. I still wish to this day they'd release 3+ GHz phenoms :(
    Reply
  • ImmortalZ - Wednesday, April 23, 2008 - link

    Any MPEG4 AVC video encoded at Profile 4.1 or lower is fully accelerated by today's GPUs. Scene releases from the past few months confirm to this - and even with this, most of the older release are still compatible given you use the proper filters. Reply
  • ImmortalZ - Wednesday, April 23, 2008 - link

    * By Profile I meant Level. Reply

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