Here is a quote from Anandtech's nForce review:
<< One feature of AMD's Hyper Transport bus is the ability to support multiple virtual channels. We believe that a particular implementation of this is what NVIDIA is calling StreamThru as a part of their nForce technology.
StreamThru basically guarantees that regardless of what other demands are placed on the chipset, the devices that are latency and bandwidth critical will receive the ultra fast access and bandwidth to main memory that they need in order to operate properly.
Devices that are latency and bandwidth dependent are known as isochronous devices, those that aren't latency dependent (meaning they can be interrupted for a bit in order to let another device occupy some time) are known as non-isochronous devices.
An example of an isochronous device is the integrated 10/100 network controller in the MCP. NVIDIA's internal architecture, made possible courtesy of Hyper Transport's support for virtual channels, will allow the 10/100 network controller to always get the bandwidth and low latency access to the graphics, CPU and main memory that it needs to operate without any interruption.
This is what NVIDIA is calling StreamThru but really the technology is made possible by Hyper Transport. It is useful nonetheless.
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As you can see, the NIC is only an example of device that is treated as isochronous by the chipset. Basically, it means that one can slap any NIC, and make a good use of the StreamThru technology. My guess is that nVidia has an agreement with Realtek to supply NICs with the chipset. Abit simply got the newer version.
Leo