One of the key architectural differences between NVIDIA’s nForce3 line and other competing solutions from VIA and SiS is their single-chip architecture. If you recall the design of traditional system chipsets, the chipset is usually composed of two chips: a North Bridge and a South Bridge. The North Bridge traditionally houses the memory controller, and is responsible for interfacing with the CPU as well as AGP. Of course, now that AMD has integrated the controller on the CPU itself the first role (memory controller) is no longer performed on the North Bridge. Meanwhile, the South Bridge handles I/O duties such as storage, USB, PCI, and networking.
The North Bridge and South Bridge are linked together by a serial pathway, with the actual implementation varying depending on the manufacturer. SiS is well known for its MuTIOL link, providing up to 1GB/sec of peak bandwidth, while VIA’s V-Link peaks at 533MB/sec.
With nForce3 150 and nForce3 250 however, the North/Bridge South Bridge architecture is scrapped in favor of a single chip design. In theory, this should reduce latency. In addition, the single chip architecture gives motherboard manufacturers more freedom with their board designs, giving them more room to add additional onboard features such as FireWire and additional storage controllers. Single chip designs also ease inventory management for motherboard manufacturers.
SiS’ SiS735 was an extremely popular single-chip solution, but SiS ultimately decided to abandon the single chip architecture. They found that integrating new features such as upcoming storage technologies and USB 2.0 often required a complete chip redesign, ultimately increasing the amount of time it took for them to bring new chipsets to market. With the North Bridge/South Bridge architecture, you can just swap out the older South Bridge with a newer one that supports all of the latest and greatest technologies. If true, this may help explain why it took NVIDIA so long to bring nForce3 250 to market.
One of the chief complaints that was voiced against nForce3 150 was its HyperTransport implementation, NVIDIA was limited to just 600MHz, while VIA’s K8T800 supported 800MHz. NVIDIA made matters worse by limiting HyperTransport’s upstream connection on nForce3 150 to just 8-bits, half the 16-bit width found on other solutions.
For nForce3 250, NVIDIA has completely reworked their HyperTransport interface. 800MHz HyperTransport support has been added, and nForce3 250 provides 16-bit links for both upstream and downstream. We also noticed that the nForce3 250 chipset retains the ability to lock the AGP frequency, which is an important feature when overclocking.