Not all hard drives are compatable with all systems If you do find a brand that is compatable, it does not matter if its a 10 gig or a 200 gig, as long as the brand is compatable
drives over 20gig on older systems like p1 & early p2 couldn't be seen properly or not at all & doesn't matter on the hd manufacturer. the bios determines if it sees the hd not vice versa.