SiS 655FX and 655TX - Similar but Different
SiS has been one of the backbenchers in the Intel Pentium 4 platform. In fact, the main reason behind the SiS success in the Pentium 4 realm is because of Intel support - but why do we say this?
During the RDRAM debacle that Intel was caught up in, Intel was unable to produce DDR supporting chipsets for its Pentium 4 systems. With VIA refusing to pay any royalties, Intel approached SiS to produce its DDR based Pentium 4 chipsets which is how the SiS 645 came to pass. From here the development just continued towards its latest products, in fact, SiS hasn't been given its dues, as they were the first to produce a Dual Channel DDR Pentium 4 chipset, the original 655 chipset with 533MHz FSB support and Dual Channel DDR-333, the fastest Dual Channel controller of the time.
Today SiS has moved on to its two new products for the Pentium 4, based directly on the 655's success, the two new comers are the 655FX and 655TX. The TX is to the 875P as the FX is to the 865PE. Both have their respective common features with one adding more for extra performance, at a slightly higher cost.
Firstly the 655FX was the first of the Dual Channel DDR-400 chipsets from SiS to support the Pentium 4 running an 800MHz FSB. This chipset supports 400/533 and 800MHz CPU's so all the latest and all the legacy Pentium 4 and Celeron 478 CPU's can run on the 655FX. The memory controller is a direct descendant of the 655 controller, with additional tweaks and support. Firstly the latency issues that were caused on the 655 have been addressed as well as support for DDR-400. This allows for a maximum of 6.4GB/s, equal to that of the Intel and VIA offerings.
The 655TX is based directly on the 655FX technology, but simply adds Advanced Hyper-Streaming technology. SiS describes the operations of Hyper-Streaming as similar to a pre-fetcher engine that allows reduced latency across the memory, CPU and AGP buses to permit faster bus access and reduced data retrieval times.
Both chipsets use the SiS MuTILO interface for its connection to the Southbridge. This MuTILO is the most bandwidth friendly of the interconnecting bridges with 1GB/s support. This in theory can allow for Gigabit Ethernet, four SATA ports, Firewire, PCI Express and standard PCI access all at once with minimal latency.
The Southbridge of choice for the 655FX and TX is the new 964. This Southbridge adds support for Serial ATA RAID functions as a standard feature, eight USB 2.0 ports, six PCI master, AC'97 Audio version 2,2 and 10/100 Ethernet.
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