Articles: Memory

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We have already told you a number of times on our site that very soon Intel is going to introduce a new 800MHz Quad Pumped Bus in systems based on Pentium 4 processor family. This is scheduled to happen in the middle of April and will be accompanied by the launch of new chipsets (Springdale and Canterwood) that support such system bus frequency and 200MHz FSB frequency. The boost of FSB bus bandwidth will require faster memory to use up the bigger processor bus bandwidth. While the new DDR II standard is far from entering the mass production phase yet, Intel suggests that we use dual-channel DDR400 SDRAM in new Pentium 4 based platforms. This fact means that DDR400 SDRAM is going to give up its reputation of the “memory for overclockers” and become a mainstream product. This is the way Intel views the near future of the memory market:

But what about the Intel’s good old rival, AMD? Right now, Athlon XP family processors use 333MHz system bus and 166MHz FSB frequencies. Considering that most chipsets for Athlon XP quite naturally show their best performance in case the system and memory buses work synchronously, DDR333 SDRAM seems to be a preferable memory type for modern Socket A platforms. Thus, after the arrival of Pentium 4 with the 800MHz bus, AMD can find itself lagging behind as concerns the employed memory type. Of course, it’s theoretically possible to use DDR400 SDRAM with Athlon XP using 333MHz bus. But numerous tests prove that this brings no perceptible advantage from the performance point of view, or even slows the system down.

That’s why the transition of Athlon XP processors to a 400MHz bus is vital today. A faster bus would allow using the advantages of the upcoming DDR400 industry standard. In the end, this should increase the performance of Socket A processors without raising their clock frequencies. Such an opportunity must be most appealing to AMD: Thoroughbred and Barton CPU cores, which are available by AMD today, have practically reached their frequency maximum. So, it would be a nice thing for AMD to raise the performance of their processors in some other way than by mere overclocking.

Meanwhile, AMD keeps silent about its plans on making a faster bus, and only says that company engineers are considering this possibility. The Alpha EV6 bus, currently used in Athlon XP CPUs, can in theory work at 400MHz, but there can arise some problems with chipsets and mainboards. Manufacturers just didn’t intend their products to be used at 200MHz FSB. This may lead to lower stability of Socket A systems and AMD just can’t allow this to happen. As a result, the release of Athlon XP with a 400MHz bus may require the development of new chipsets and mainboards (or new revisions). But the expediency of putting new effort and resources into making up new products for Athlon XP is questionable as the Socket A CPU line from AMD is going to stop its evolution soon.

Nevertheless, in spite of all those problems, we are inclined to think that the next Athlon XP 3200+ processor may be released in two variants: for the 333MHz and 400MHz bus. But even if AMD doesn’t bring itself to such a move, the 400MHz bus is sure to become widely used among overclockers. As soon as they get DDR400, they wouldn’t miss the chance of getting some speed-up through overclocking the FSB.

We are going to answer a few important questions in this article. First, we will estimate the performance growth provided by the use of the 400MHz bus, considering DDR400 has poorer timings than DDR333 and DDR266 modules. Second, we will check the capabilities of available DDR400 memory modules. Third, we will see how memory timings affect the overall system performance.

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