When I started testing SiS755, a new chipset for Athlon 64 processors from Silicon Integrated Systems Corporation, a story of two years ago came to my mind. Back then, in the fall of 2001, chipset makers were only starting to produce chipsets with DDR SDRAM support intended for Socket A platform. AMD, VIA and ALi were the first companies to release such products. SiS was a little late then, but the tardy SiS735 turned to be the fastest Socket A chipset of that day, much to the surprise of the community. SiS showed the strength of the company’s engineering team, which managed to build the most efficient memory controller for DDR SDRAM. As a reaction to SiS’ success, other manufacturers were hastily releasing their products revisions with faster memory controllers.

This old story seems to repeat itself now. First of all, SiS is again a little late with a chipset for the AMD Athlon 64 platform since the mainboards on VIA K8T800 and NVIDIA nForce3 150 have long been in the market already, while analogous mainboards on chipsets from SiS are yet to arrive. On the other hand, the sales of the Athlon 64 processor itself have been low enough so far, so some delay won’t tell on the potential sales of the upcoming SiS chipsets. And they do come up along with SiS755-based mainboards. So, we decided it is high time we offered you a detailed coverage of the capabilities and performance of the SiS755 chipset. I am very excited to find out if SiS755 can repeat the success of the SiS735 predecessor. What surprises has SiS prepared for VIA and NVIDIA? Will it once again prove a manufacturer of high-performing chipsets?

SiS755: Closer Look

So, SiS755 is the first chipset from the series SiS is going to offer for the Athlon 64 processor family. Looking just at its formal specifications, SiS755 does not seem a jewel at all. I don’t mean to say that it lacks functionality; it is at the same level with other modern chipsets, but not any better than those. The specifications are actually quite ordinary according to the today’s standards.

As the flowchart suggests, the chipset consists of two chips: the SiS755 North Bridge and SiS964 South Bridge (although nothing prevents mainboard manufacturers from using other latest South Bridges from SiS as they are all pin-compatible).

SiS755 supports HyperTransport bus for communication with the processor with a bandwidth of 1.6GB/s. In other words, the bus is 16bit wide and works at 800MHz both ways. SiS755 is free from the drawback of the competing chipset from NVIDIA, nForce3 150, which has a cut-down version of the HyperTransport bus with a frequency of 600MHz and a width of 8bit one way.

SiS755 also contains the AGP 8x controller with Fast Writes support. An important note: the new chipset is also free from the drawback of the VIA K8T800 allowing more flexible control over the AGP (and PCI) divisors. It means we won’t have any problems with AGP and PCI devices when overclocking the CPU by boosting the FSB frequency. Moreover, like the NVIDIA nForce3 150, the new SiS chipset allows clocking the AGP/PCI frequencies asynchronously with those of the FSB. You can just lock the AGP frequency at its regular value. That’s truly the most important thing when you overclock the processor by raising the bus frequency.