Aah, gisteren wist The Register ons nog te vertellen dat het i820 / Rambus probleem zich alleen voordeed bij Intel planken, vandaag ligt de situatie al weer anders... Het probleem lijkt nu gewoon te liggen in de hoog frequente signalen van de Rambus lijntjes, die krijgen ruzie met elkaar bij gebruik van 3 RIMMetjes:
The i820 and the i840, the latter of which was formally released today, use identical Rambus interface circuitry, he claimed. And there are other mobos rather than Dell (sorry Intel's) that fail with three RIMM modules.
"These failures have to do with multiple back to back pipelined transfers from multiple devices on the bus. The guys at Hard OCP were given accurate information. This is a key feature of a Rambus system, to have multiple devices accessed simultaneously and driving the bus in a pipelined back to back fashion. This is where the only performance advantage for the bus will come from," he says.
And the failures are not just poor board design, with some serious theoretical issues involved -- resonance being the key one. "Buses are running into quarter and half wavelength resonance effects which cause voltage margin and timing margin violations. No re-engineering of the drivers, board, or receivers will fix this problem with three RIMM systems.
"Resonance effects are not limited to three RIMM systems, however, the effect here is much greater. There are reasons to believe that resonance problems can occur with two RIMM systems under extreme circumstances. It would literally take years of simulation time to simulate most of the possiblities," he adds.
However, poorly designed boards will exhibit the problems more frequently than better designed boards, while server and workstation mobos (i840) are designed with more margin, and hence less chance of failure.
Check The Register voor meer info.