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VIA's KT333 chipset: Socket A bonanza


Socket A bonanza
— 12:00 AM on February 20, 2002

VIA IS TAKING the wraps off its new Socket A chipset today, the KT333. This successor to the impressive KT266A chipset promises to take AMD's Athlon XP to the next level, provided the Athlon can squeeze some extra performance out of 333MHz memory while reaching through a 266MHz bus.

We decided this was the perfect occasion to catch up on something we've been meaning to do for a while: a gigantic Socket A chipset round-up. So we rounded up as many of the KT333's competitors as we could muster, and we've tested no less than seven different chipsets—including the SiS 745 and NVIDIA's nForce—in nine different configurations. So which chipset is the best match for that shiny, new Athlon XP processor you've been eyeing? Keep reading.

The DDR333 challenge
Bringing DDR333 to AMD's present Socket A platform presents several formidable challenges. First and foremost, the Athlon XP's front-side bus currently runs at only 266MHz, so it can only transfer 2.1GB/s. DDR memory at 333MHz offers as much as 2.7GB/s of bandwidth. Hence the challenge.

Now, that fact alone isn't the end of the matter. The current DDR266 chipsets don't deliver completely on their promise of 2.1GB/s of throughput, so there is a little room for improvement. On top of that, components in the system other than the CPU can make use of extra memory bandwidth, even if the CPU is bottlenecking on its front-side bus. Hard drives and other I/O devices will use direct memory access (DMA) to read and write data to memory without passing data across the front-side bus.

Still, the prospects for performance gains when putting DDR333 memory on a 266MHz front-side bus aren't great. The nastiest part of the problem is that, by definition, the 333MHz memory controller will run out of sync with the 266MHz front-side bus. Running the FSB and memory clocks at different speeds can introduce additional latency into the process of accessing memory, which can offset any performance advantage afforded by the faster memory clock. Add it all up, and the best one can hope for is incremental performance improvements.

Not only that, but DDR333 memory faces a few challenges of its own. The standards body that decides memory specs for the industry, JEDEC, hasn't yet finalized the DDR333 spec. That fact hasn't stopped chipset makers and memory resellers from selling "DDR333" or "PC2700" products, but such products can't officially conform to the unborn JEDEC DDR333 standard. VIA says they expect the final DDR333 standard to be approved by March. Until then, be aware that DDR333 DIMMs you might buy won't necessarily comply with the final JEDEC spec.

Incidentally, back when we did our Pentium 4 chipset round-up, only SiS's 645 chipset supported DDR333 memory. We asked VIA when they would support DDR333, and they told us they would support it when the time is right. I'm not sure the time is quite right yet, but it is getting closer.