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LOSTCIRCUITS
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| Intel Pentium4 840 Extreme Edition and 840D .... the name of the rose ... | |
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(Review by MS June 20, 2005) |
| AMD Athlon 64 3800+ (Venice) |
Summary
Dual cores are becoming mainstream. Both Intel and AMD's flagship CPUs are using two cores on a single die, albeit, with different interfacing strategies. In addition, Intel offers the ExtremeEdition with HyperThreading capability to double the logical cores to a total of four units. On the other hand, the dual cores are offset by a lower clock speed, at 3.2 GHz, the Smithfield core lags 600 MHz behind the fastest single core Pentium4 offered by Intel.
There are benchmarks, there is thread collision, and there is exuberant performance in thread level parallelism-optimized applications. And then there is power consumption. Under peak load, we measured 147W isolated CPU power but that's only the beginning.
Moore’s law regarding the doubling of transistors every 18 months has been upheld for a number of decades. In addition, about every 18 months, we have witnessed almost a doubling in CPU clockspeed but in the last year, the ramp has shown definite signs of reaching a plateau. The reasons have been well known for quite some time as we pointed out in our original article on processor power consumption and it is clear that, at least in engineering circles, the end of the speed race as we know it has been anticipated for quite some time.
In about every company known to man, on the other side of the engineers is the marketing camp, comprising those who claim to pay the engineers (there is a reason that marketing people end up in marketing). The primary goal is to promote their products as better than anything the competition has to offer and that’s a good thing. There are, by the very nature of marketing, also usually some overzealous efforts associated with marketing, leading to white lies and not so white lies but I digress, this is about the greatest Intel CPU ever and not about marketing.
In all honesty though, of all CPUs we have ever looked at here, the new Intel Pentium4 840 Extreme Edition is probably the one that is the most controversial and difficult to place, even from a marketing standpoint. After using it for a number of weeks now in 32-bit and in 64-bit WindowsXP environments, we have a plethora of data with respect to raw performance and raw power, but data sometimes still rather poorly describe the essence of an entity as complex as the ‘840 ExtremeEdition.
From the top, the '840 looks about just like any other LGA 775 Pentium4
Briefly, as everybody knows by now, the buzz strategy is to move away from single cores and instead to integrate symmetric multiprocessing on a single chip. The single chip factor is essential in order to reduce complexity of the layout as well as to eliminate space constraints that arise just from having to accommodate two physical coolers. In addition, the cost equation clearly favors a single chip design. Consolidation of multiple cores has been at least a hypothetical issue at Intel since 1989.
In the case of AMD’s Athlon 64 X2, the dual core has one distinct disadvantage, that is, each core has essentially only access to a single channel of memory. That is, both cores have to go through the system request interface and a crossbar switch to get access to the memory and, in a situation where both cores simultaneously request data, this can lead to contention. A true SMP solution, on the other hand, can utilize both channels for each CPU and, furthermore, take advantage of the cache-coherent Non Uniform Memory Architecture (ccNUMA) which provides memory access through two distinct buses, namely the direct memory interface to the near memory and the HyperTransport to the far “node”, i.e., piggybacking off the second CPU. In other words, each CPU has hypthetically access to four channels of memory.
For Intel's bus interface, it does not matter whether there is a single dual core CPU or two separate single core processors, the bus is shared anyway
In the case of the Pentium4, the question about dual core vs. SMP comes out to as a wash, at least in terms of the memory bandwidth, since even two physically separate processors will share one bus.
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Pentium 4 840D (dual core) |
next page: => The HyperThreading Paradox =>
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