And it wasn't incorrect either. -um is the ending for neutrums (actually neutra) and -a is the plural thereof.
True, except in that Pentium is an English neologism, and thus is pluralized like an English noun. Don't get me started on the plurals of octopus or virus, please.
It's odd, but someone actually downvoted me for getting you to clarify that. Haters gonna hate, I guess.