ATI's Mobility Radeon 9700 - What's in a name?

Video Memory Bus - Hasta la vista, buses...

One of the most unaddressed topics for mobility products has been memory bus termination. Buses are routed on high speed PCB traces that work in the similar sense to transmission lines. If you leave the "lines" open, electrical signals could reflect back and distortion with the communication of the controller and controlled devices. Signal distortion can produce or contribute to things like erroneous bits in data, false memory addresses, etc. The way to avoid this is to use termination to close each end of the buses with resistor circuits.

As far as we know, there are no mobile GPU designs that use full termination (also called parallel termination). Serial and no termination have been the traditional methods used for virtually all notebook designs. Note that ATI's own brand of desktop cards implement full termination. This is in the sense of the GPU memory bus not the AGP bus, which are independent of one another.

This is what Rahul Sood, President of Voodoo PC, had to say on the topic:

There are traditionally three memory termination options depending on trade-offs amongst performance, power consumption and PCB space. They are: no termination (lowest speed, least PCB space requirement), serial, and full termination (highest speed, largest PCB space requirement).

For short traces (< 2 inches), the so called "half parallel" termination, essentially full termination without the series resistor, is a good compromise between performance and space requirement.

The implementation of full termination comes with several trade offs, like increased power consumption/thermal emissions and an increase in necessary PCB real estate, while the system generally benefits from performance and the ability to crack up the clocks. We have been told that there may be a fully terminated Mobility Radeon 9700 design popping up sometime soon, but the details are still sketchy at this point.