"the Airbus has more than one ADIRU"
Interesting. The B777 has only one ADIRU, plus a secondary unit called SAARU. The latter will take over attitude and airdata indications (but no lat/long IRS data) in case of a(n) (partial) ADIRU failure, but I wonder how Boeing has solved the problem of identifying an ADIRU failure in the first place. Majority vote is not an option with only one unit installed, is it?
Or does the B777's ADIRU have more elaborate internal fault recognition capabilities and more built-in redundancy than the Airbus's? (I can imagine that it is probably merely a matter of defining what components constitute a 'unit', but then the use of the same acronym is sort of puzzling.)
Sorry for being off-topic...