The House That Silence Built

Can a portable hard drive be formatted to work with both Windows and Mac OSes? Hex suddenly stopped being able to work with both at the same time -- it did when I experimented. I swear to god, Hex totally was able to store a file put on it by Holly and then Ziggy copied it over.

So now I'm thinking about a portable hard drive by Seagate or whomever. I really don't want to leave my music collection behind or go through a stack of DVDs to transfer it all.