The high speed Yellowstone interface will connect the console's core memory with the Cell processor cluster, which will in turn be connected up to the graphics chip (though to be an evolution of the PS2's Graphics Synthesizer (GS)) using another Rambus technology - the ultra high-speed Redwood interface.
Fancy crunching some numbers? Fine - Yellowstone offers data rates of between 3.2 and 6.4 Ghz, which gives it between 50 and 100Gb of memory system bandwidth, while the Redwood interface runs at anywhere between 400mhz and 6.4ghz, boasting performance up to ten times faster than current best-of-breed processor buses.
What that means in real teams is that if there's going to be any bottleneck in the PS3 architecture, it's unlikely to be the RAM interfaces. The rest of the system's architecture is gradually beginning to fall into place as well, with more of the wraps coming off the Cell processor thanks to the filing of patent applications for the architecture - and despite the misgivings of some commentators, the fact is that we have more solid information now about the PS3 than about either the Xbox 2 or the "N5", as Nintendo's next console offering has been unofficially christened.