Intersymbol interference is the big issue here. At this frequency the
"eye pattern" closes down due to ISI on the single ended
Rambus channel. Other noise harmonics and standing wave
issues will complicate the problem, though.
Per Torstein R=F8ine wrote:
> As a hobby, I like to follow news and rumors about the PC platform.
> The other day, "The Register" had a story called "Rambus Meltdown a
> sorry tale of fudge, mudge and kludge" that may be interesting to
> si-list readers (http://www.theregister.co.uk/990608-000022.html).
> The rumors say that Intel can't get their new chipset running stable
> with a 133MHz front side bus frequency and 800Mhz (400Mhz, on both
> clock edges) Direct Rambus frequency. I can imagine that producing
> inexpensive motherboards with such high frequencies is a challenge,
> but it seems like Intel's problems are worse than expected.
> I was wondering: Could Intel's problems be related to the fact that
> the Rambus frequency is exactly the third harmonics of the FSB
> frequency? Isn't this especially unfortunate noise-wise? Does any of
> you have any experience to share regarding specific unfortunate
> combinations of on-board frequencies?
> The reason I was wondering about this is that, according to the
> article, Intel is considering lowering the Direct Rambus speed to 712
> MHz, which is 16 Rambus data words for each three FSB data words, down
> from 18.
> Per Torstein Roeine email: firstname.lastname@example.org
> University of Oslo phone: +47 22 85 24 52
> Dept. of Informatics, Microelectronics Group fax: +47 22 85 24 01
> Box 1080 Blindern, N-0316 OSLO, NORWAY
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