SiS655FX, VIA PT880 and i865PE: Try to See the Difference

Historically, Intel has always been the trend-setter in the market of Pentium 4 chipsets and the situation has been usually following this scenario: Intel implements some innovations in its chipsets and then other manufacturers use them in their own products a little later. Of course, it’s not all that simple in reality, for example Intel added USB 2.0 support after VIA and SiS did, but overall this is a game of mimicking Intel’s gestures. Thus, launching its i865 and i875 chipsets about a year ago, Intel outlined the basic features of a modern Socket 478 chipset: support of the 800MHz Quad Pumped Bus, a dual-channel memory controller with support of DDR400 SDRAM, plus Hyper-Threading, SerialATA and RAID. Today you can see all this implemented in the new chipsets from VIA and SiS and the three columns in the following table often duplicate each other:

Yes, the chipsets are very similar in their external characteristics (about which the user cares most). In fact, the only significant deviation is the PT880’s supporting ECC, although this feature is unlikely to be called for in this budget solution. As for the CSA port in the i865PE, VIA and SiS were not enthusiastic at all about this Intel’s innovation and preferred to stick to the usual network controllers attached via the PCI bus. That’s reasonable since CSA is only supported by the Intel 82547 chip, a very expensive solution you seldom meet in consumer products. Moreover, Intel is going to abandon this bus in the next generation of its chipsets.

Again, other parameters of the three chipsets are identical. We can of course delve deeper into the architectural, rather than specification, differences. The chipsets use different buses for connecting the North and South Bridges. Intel’s bus provides a bandwidth of 266MB/s, while VIA and SiS employ faster solutions with a bandwidth of just over 1GB/s. These two buses differ from one another, too. SiS has a 16-bit bidirectional bus working at 533MHz frequency and VIA offers a 32-bit 266MHz bus. In spite of the obvious disparities in the characteristics of the two buses, you will hardly notice any difference in practice: the devices attached to the South Bridges work at similar speeds. There are also different memory controller implementations as well as various exclusive technologies (which mostly serve marketing purposes) for increasing bandwidths and reducing latencies. VIA boasts its DualStream64, while SiS has the HyperStreaming Engine.

But let’s turn to palpable matters, relevant for the end user. SiS655FX features the highest flexibility of the memory controller, offering numerous divisors for the memory frequency at 200MHz FSB. This allows clocking memory at the standard frequencies (266/333/400MHz) as well as higher ones like 433, 466 and 500MHz. VIA PT880 and i865PE can’t do that. However, the fastest mode for the SiS655FX is still the synchronous one, so there is not much practical sense in this abundance of memory settings. The memory controller of the SiS655FX can work with memory in two modes: using two 64-bit channels or accessing memory through a 128-bit channel. Again, the positive effect of this setting is only felt in a few specific applications.

The memory controller of the VIA PT880 chipset was promised to have certain unique features, too. Particularly, VIA Technologies mentioned support of Quad Band Memory, a technology developed by Kentron. The harsh market realities made the company give up its original plans – the support of QBM SDRAM is not mentioned in the specifications of the VIA PT880.

The overclocking capabilities of a chipset highly depend on the opportunity to asynchronously clock the FSB and AGP/PCI buses. That is, if clock rates of the peripheral buses grow up as you increase the FSB frequency, you can hardly hope for good processor overclocking. Intel chipsets have long been able to clock AGP/PCI buses independently, keeping them low when the FSB frequency grew. Chipsets from the Taiwanese competitors couldn’t boast this ability until recently. However, this situation has changed: VIA PT880 and SiS644FX can both clock the AGP/PCI asynchronously and independently of the FSB clock rate.

Anyway, even an excellent chipset needs to be implemented nicely in the particular mainboard. So let’s save our final verdict until we play a bit more with the participants of our today’s review.