I don't know where TFA got the "globally addressable PB". I think someone was misquoted.
I can't find any mention of it in the NCSA webpages, and no shared memory system exists on this level, ccNUMA or otherwise (NASA Ames has a 4TB altix system, which is evidently the largest in the world that is publicly acknowledged).
Software distributed shared memory hasn't really gone anywhere either, so I think someone was fantasizing when they wrote the article... globally accessible filesystems, sure, but shared memory is something else altogether...
If mathematically you end up with the wrong answer, try multiplying by the page number.