AMD's 760 Chipset: DDR for the Athlon is hereby Anand Lal Shimpi on October 30, 2000 5:29 AM EST
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Illustrating the need for DDR - Linpack
A benchmark that has always come in handy but has never really been used on AnandTech is something known as Linpack. The guys over at Ace's Hardware have been using Linpack for quite some time, and it is to them that we owe the discovery of the benchmark as we will begin using it as well to help analyze performance.
While it may be hard to get anything out of the above graph at first sight, keep in mind that all of the blue lines represent the Intel Pentium III 1GHz while the two green lines (one dark one light) represent the Athlon 1GHz.
What Linpack allows us to do is notice how the performance of the various CPUs/platforms drops off as the size of the data set being manipulated increases. For example, if you notice at the very top of the chart is a peak shared by the two AMD setups. This peak occurs at a data size of around 64KB, which is exactly the size of the Athlon’s L1 Data Cache. The performance then drops until the data size reaches around 384KB which is the end of the Athlon’s on-die cache, and this is where we see the two Athlon lines separate, the darker line representing the performance of the AMD 760 which features a faster DDR memory bus. This faster bus translates into less of a performance hit when going from on-die cache to system memory since the system memory is performing more like the on-die cache (but still far from coming close in the big picture).
The picture is a bit different when it comes to the Pentium III as the CPU peaks much later than the Athlon, however the big drop off again occurs after the Pentium III’s 256KB on-die cache is filled (256KB L2 + 16KB L1 - 16KB duplicated L1 click here for more info on the Pentium III's Inclusive L2 Cache).
It is this tail that we need to pay attention to since it represents what happens when an application doesn’t conveniently fit within the Athlon’s large L1 and/or L2 cache.
Zooming in on the tail from above we see a very interesting picture. Let’s start from the bottom and go up. The lower the line is the more limiting the memory solution is to the performance of the CPU.
At the very bottom of the list we find the i820 chipset which boasts a hefty 1.6GB/s available memory bandwidth however, in a real world scenario, isn’t able to even outperform the i815’s PC133 SDRAM. In the end, the i820 chipset is holding the Pentium III back more than its helping it.
The i840 is represented by the second to last line. While it offers superior performance in comparison to the i820 it is still pretty low on the performance scale, not to mention its price is much higher than everything else on this chart.
Now here’s the interesting part, while you would expect the i815 to follow as the next slowest, you don’t see that. Instead, it’s the VIA KT133 chipset that follows. This means that the KT133 chipset provides less memory bandwidth to the CPU than the i815E does, with both memory buses clocked identically at 133MHz.
Finally we have the AMD 760 with its PC2100 DDR SDRAM coming out on top, not only offering the best performance out of the five solutions featured in the chart but also giving the Athlon the ability to scale and perform even better than it already has been doing with the VIA KT133 chipset.