Articles: Memory

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Although Core 2 Duo processors still use an external memory controller, located in the chipset's North Bridge, the mentioned features of the new micro-architecture help them challenge Athlon 64 X2 CPUs, which have a memory controller integrated into their core, in terms of memory performance. The graphs below show you the results of our measuring the effective memory bandwidth and latency in systems based around an Intel Pentium D 960, Intel Core 2 Duo E6700 and Athlon 64 X2 5000+. DDR2-800 SDRAM with 4-4-4-12 timings was used in each case:

As you see, the Core 2 Duo platform features higher memory performance in comparison with the Pentium D system in practice, not only in theory. Although the two processors from Intel access memory through the same memory controller integrated into the chipset's North Bridge (this test was performed on an i975X-based mainboard), the choice of the CPU affects the result greatly. The Core 2 Duo can ensure a 10% higher memory bandwidth and much lower data access latency (from 20% to 40% depending on how efficient the data pre-fetch algorithms are in a particular application). The Core 2 Duo is obviously superior to previous-generation NetBurst processors when it comes to using the memory subsystem efficiently.

It is quite interesting to compare the real-life performance of the Core 2 Duo platform with that of the Athlon 64 X2 platform especially since they use different approaches to placing the memory controller. Contrary to the Core 2 Duo, the Athlon 64 X2 (in Socket AM2 design) has an internal DDR2 SDRAM controller, integrated right into the CPU core. The integrated controller provides a very high memory bandwidth. The substantial advantage over the Core 2 Duo platform is not to be wondered at considering that in Intel's systems the speed of data transfers between the CPU and memory is limited by the bandwidth of the FSB. As a result, the DDR2-800 SDRAM memory subsystem is about 40% efficient on the platform with the new Intel CPU and 55-60% efficient on the Athlon 64 X2 platform.

As for the memory latency parameter, two out of three test utilities show that the Core 2 Duo platform is capable of achieving lower memory latency than the Athlon 64 X2 system. This result is obviously due to the data pre-fetch algorithms employed by the Core micro-architecture. Those algorithms prove to be very helpful in many cases. So, even though with an external memory controller, Core 2 Duo processors have high performance in applications sensitive to memory speed. 

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