SiS (Silicon Integrated Systems) has rolled out a long-expected chipset for Pentium 4-based PCs that supports dual-channel PC1066 RDRAM (Rambus dynamic RAM), the SiS R658.

Until last year, all Pentium 4-based computers used PC800 RDRAM. That changed when Via and Intel, among others, released chipsets that brought support for DDR (double data rate) RAM and SDRAM (synchronous data rate RAM) to P4-based desktops.

That development brought forth a surge in shipments of Pentium 4-based PCs based on these memory types, which are generally cheaper than RDRAM and, in the case of DDR, offer comparable performance to PC800 RDRAM in many applications.

While Pentium 4-based PCs that use SDRAM and DDR RAM have found widespread acceptance in the mainstream market, RDRAM continues to find adherents at the high-end of the market, where its performance advantages have the most impact.

Aimed at power users, the R658 supports both 800MHz RDRAM and the newer 1066MHz RDRAM, which offers greater data throughput than PC800 RDRAM and DDR RAM, while taking advantage of the 533MHz front-side bus (FSB) — which connects a PC's processor with the chipset — supported by the latest versions of the Pentium 4 processor. Earlier versions of the Pentium 4 use a 400MHz FSB.

The R658's support for dual-channel PC1066 RDRAM, which has a maximum memory bandwidth of 4.2GBps (gigabytes per second), allows a 50 to 100 percent increase in memory bandwidth compared to DDR, SiS said in a statement.

SiS expects the resulting improvement in overall system performance offered by PC1066 RDRAM to become more pronounced as Intel cranks the clock speed of the Pentium 4 to 3GHz and beyond. That will happen later this year, when Intel is expected to begin shipping the 3GHz version of the Pentium 4. Currently, the fastest Pentium 4 chip has a clock speed of 2.53GHz.

The R658 can support up to 4GB of PC1066 or PC800 RDRAM and also offers support for AGP 8x graphics. Details on pricing and availability were not immediately available.