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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  • JarredWalton - Wednesday, April 23, 2008 - link

    I've seen nothing to suggest a faster HyperTransport bus would help AMD much. You need to compare at the same CPU speed; if you raise the HT bus to 250 MHz that represents a 25% overclock of the CPU as well, so of course it helps performance a lot. Try comparing:

    Athlon X2 4600+ 2.4GHz
    Run at 200 HTT and 12X CPU vs. 240 HTT and 10X CPU

    Athlon X2 4800+ 2.5GHz
    Run at 200 HTT and 12.5X CPU vs. 250 HTT and 10X CPU
    (Note: the 12.5X multiplier vs. 10X may have an impact - half multipliers may not perform optimally.)

    Athlon X2 5000+ 2.6GHz
    Run at 200 HTT and 13X CPU vs. 260 HTT and 10X CPU

    Now, the one thing you'll also have to account for is memory performance. At default settings (i.e. DDR2-800), you get different true memory speeds. The 12X CPU will end up at a true DDR2-800; the 12.5X will end up at DDR2-714 (CPU/7 yields 357MHz base memory speed); the 13X will result in DDR2-742 (again, CPU/7 yields 371 MHz base memory speed). For the "overclocked HT bus" setups, you'll need to select the same memory dividers to get apples-to-apples comparisons, which depending on motherboard may not be possible.

    Unless you can do all of the above, you cannot actually make any claims that HyperTransport bus speeds are the limiting factor. I imagine you may see a small performance boost from a faster HT bus with everything else staying the same, but I doubt it will be more than ~3% (if that). HT bus only communicates with the Northbridge (chipset), and the amount of traffic going through that link is not all that high. Remember, on Intel that link to the chipset also has to handle memory traffic; not so on AMD platforms.
    Reply
  • ghitz - Wednesday, April 23, 2008 - link

    The e8400 performance/power usage is outstanding and will be great value once the G45 boards trickle in. I can't wait for those G45s!
    Reply
  • ap90033 - Wednesday, April 23, 2008 - link

    So AMD STILL hadnt caught up. Thanks Good to know. Not that Im suprised.... Reply
  • natebsi - Wednesday, April 23, 2008 - link

    The bottomline is: AMD's newest CPU's are bested in nearly every single benchmark by an Intel CPU thats been out like, what, a year?

    I have no love/hate relationship with either Intel or AMD, but thats just sad. I predict many more losing quarters for them, though I don't know how many more they can take...
    Reply
  • Griswold - Thursday, April 24, 2008 - link

    Thanks for that null-posting. Reply
  • najames - Wednesday, April 23, 2008 - link

    As a long time AMD only user, I just bought an Intel Q6600 on impusle from Frys.com for only $180. I was looking at a 780G solution and thought, I'll get the Intel quad and a similar Intel based solution for doing video processing work. Oops, I found out the only current Intel mATX is the G35 is from Asus, ONE BOARD, huge selection to choose from huh?

    I'll either sell/return the unopened CPU or buy a P35 board and graphics card. I could deal with a slightly slower AMD 9550 CPU and a better platform instead, tough choice.
    Reply
  • strikeback03 - Wednesday, April 23, 2008 - link

    I needed parts for a new system for the lab last week, I went with the non-integrated graphics and add-on card. Integrated graphics would have been fine for the application, but when the board plus card cost less than the ASUS G35 board (and are full-size ATX as well, which is useful) then the decision wasn't too hard. Reply
  • Staples - Wednesday, April 23, 2008 - link

    Intel graphics have always been terrible. AMD definitely has the advantage for integrated graphics and even know their CPUs can not compete, I still find myself considering one just for their graphic options. I am glad that this review points it out bringing to light that Intel graphics are just not acceptable. Whether Intel will change is a big unknown, probably not.

    I find the added emphasis over the last year of power consumption a great one. With the price of energy these days, it is something I factor into my purchase. SSE4 and a lower power consumption is the reason I am holding out for a Q9450. Hopefully by the time it actually goes into mass production (hopefully in the next two months), a decent integrated option will be out for the platform.
    Reply
  • 0roo0roo - Thursday, April 24, 2008 - link

    terrible? i used an intel 950 integrated graphics with some 1080p content, it decoded just fine with an e2200. Reply
  • derek85 - Thursday, April 24, 2008 - link

    Terrible? Yes, terrible. Besides the lame hardware they can't even write proper drivers, see how many randering problems they have in the games. Reply

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