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Single-channel chipsets for Pentium 4: SiS648FX and VIA PT800




The release of the single-channel i848P chipset with its unexpectedly outstanding characteristics, which had put Intel's Spring chipsets into an awkward position (they had two channels!) was a real success. In contrast to the past-oriented i865P with vague prospects, this chipset uses all features of Intel's modern south bridges and has no crippled north bridge components. One memory channel is locked but if 2GB RAM is enough for you, the only i848P disadvantage will be its speed.

What about the competitors? They have no dual-channel solutions for new processors (with 800MHz bus) to offer (the SiS655FX/TX and VIA PT880 chipsets are ready, but we still haven't seen any boards on them). At the same time, cheaper single-channel chipsets (the price was always an advantage of VIA and SiS) have been announced quite a long time ago, and today we are going to test the first SiS648FX and VIA PT800 solutions. But first, there's information on chipsets architectures. 

SiS648FX

Its predecessor got some very high score in its time: at that moment it was the strongest competitor for i850E+RDRAM(PC1066) tandem, and SiS648-based boards with DDR400 support were cheaper than the top Intel+Rambus combination. Unfortunately, it had no Hyper-Threading support: the release of revision B had been postponed, and without such support the chipset wasn't of much interest among top solutions. Then the company released the dual-channel SiS655 (putting aside the SiS R658), which however hadn't set any new records. And after the announcement of Intel's new Pentium 4 line with 800 MHz FSB alongside a dual-channel chipset series, SiS had been keeping silence.

Today we're going to test the first serial mainboard on SiS648FX we got. The product hasn't obtained any considerable new features, so the company just added "FX" to the name. What's changed in SiS648FX comparing to SiS648? Have a look at its block diagram.




The picture from the SiS website is out of synch with reality :). First of all, SiS648FX officially supports DDR400 (in contrast to its predecessor). Second, 800MHz FSB support is not shown in the diagram at all. There are no more differences between the chipsets. The chipset is officially coupled with SiS963L south bridge, while SiS648 is coupled with its com