266 FSB vs 133 FSB

Actually... the FSB is indeed 133Mhz. The CPU simply operates in its core
at a much faster rate than this by using a multiplier. And since all
Athlons now are DDR memory bus has double throughput of "normal" SDRAM
system with the same processor and memory. The bus clock is not actually
any higher, simply the memory and the processor are both able to
send/receive twice per 'tick' (on both the rising and falling edges of the
clock signal). But bigger numbers sell well, hence the PR+ bollocks and
people adverstizing "FSB 400Mhz" motherboards :¬)

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FWIW, it looks like Intel is going to be going to the "PR+ bollocks"
themselves at some point. Their new Pentium M processors perform at the
level of higher clocked P4M processors. In order to make Centrino sell
with the lower clock speeds eventually they're going to have to start
using a "PR" rating of some sort themselves.