Memory Controller Performance

The key to a high performing chipset lies in two areas: the FSB interface and the memory interface. Implementing the FSB link is not too difficult to accomplish well, however it is the memory controller that takes a great deal of expertise to develop and a lot of experience to perfect. It is the memory controller of these two Athlon chipsets that we'll look at first, hopefully to get an idea of what sort of performance we should expect. We ran all tests using an Athlon XP 2800+ with the FSB set to 333MHz:

Memory Bandwidth Comparison - STREAM

NVIDIA nForce2
VIA KT333
 
64-bit DDR333
128-bit DDR333
64-bit DDR400
128-bit DDR400
64-bit DDR333
Copy
945.9 MB/s
1296.2 MB/s
1071.5 MB/s
1303.9 MB/s
1069.3 MB/s
Scale
911.3 MB/s
1250.0 MB/s
1047.8 MB/s
1244.5 MB/s
947.9 MB/s
Add
1005.8 MB/s
1422.5 MB/s
1112.1 MB/s
1451.9 MB/s
1062.3 MB/s
Triad
1009.6 MB/s
1377.2 MB/s
1109.6 MB/s
1412.1 MB/s
1035.7 MB/s
Average:
968.1 MB/s
1336.5 MB/s
1085.2 MB/s
1353.1 MB/s
1028.8 MB/s

Remember that the nForce2 chipset can run in either 64-bit (single channel) mode with only one memory stick installed or 128-bit (dual channel) mode with two or three sticks of memory installed. To test the effects of going to a dual channel architecture we simply plugged in another stick of memory to enable the full 128-bit wide memory bus.

With that said, there's a pretty healthy boost in memory bandwidth when going from a single to dual channel setup with the nForce2 (25 - 40% boost in bandwidth). The move to DDR400 yields a 12% increase in memory bandwidth; the unseen penalty is an increase in latency since today's unofficial DDR400 modules don't run at the same aggressive timings as the fastest DDR333 you can buy today.

VIA's KT333 provides an impressive showing, outperforming the nForce2 by 6% in 64-bit DDR333 mode. Once you realize that a 6% advantage in memory bandwidth will not translate into any sort of real-world performance advantage, it's clear that just by looking at the bandwidth figures the nForce2 and KT333 will be very close performers.

Memory Latency Comparison - Cachemem

NVIDIA nForce2
VIA KT333
 
64-bit DDR333
128-bit DDR333
64-bit DDR400
128-bit DDR400
64-bit DDR333
Latency (clocks - lower is better)
244
244
298
305
349

Here's where we complete the picture; by looking at the latency in addition to the bandwidth we can get an idea for what sort of performance to expect out of the various configurations.

Remember the 12% boost in bandwidth we saw on the nForce2 by going to DDR400? That 12% increase in bandwidth comes at the cost of a 22% increase in latency! The increase in latency is not only due to the slower memory timings DDR400 modules run at but also because the memory bus is no longer synchronous with the FSB when running in DDR400 mode whereas DDR333 matches up perfectly with the new 333MHz Athlon XP FSB.

There's no increase in latency when going from a single channel DDR333 to a dual channel DDR333 setup on the nForce2 platform. There is a slight increase when making the same transition with DDR400 because we had to increase some of the timing delays in order to run two channels of DDR400 with the nForce2 while maintaining stability.

Also take note of the extremely poor latency of VIA's KT333 memory controller; accesses take almost 43% longer on the KT333 than they do on the nForce2 when running in 64-bit DDR333 mode.

As we proved in our original review of the nForce chipset, the bandwidth gained from going to dual channel DDR doesn't help unless you're sharing main memory bandwidth with an integrated GPU. In this case we're not and we'll be focusing on IGP performance in a later article, so we can disregard the two 128-bit nForce2 solutions for the rest of this comparison. We also have a balanced FSB/memory bus setup, meaning we have as much bandwidth going to our CPU as we do to main memory, so increasing memory bandwidth without similarly increasing FSB bandwidth would inherently yield poor returns as we're FSB limited at that point.

It's also clear that the bandwidth increase DDR400 provides doesn't offset the incredible increase in latency, leaving the nForce2's 64-bit DDR333 configuration the ideal comparison to the VIA KT333. Let's look at some real world tests:

The Test Content Creation Performance
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  • Anonymous User - Monday, October 20, 2003 - link

    Well we actually have been eagerly awaiting the release of NVIDIA's second Athlon XP chipset. Our expectations for the chipset weren't unreasonably high, which was the case with the original nForce, and there are many more launch partners this time around Reply

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