One of my late 2006 imacs has 3gb of memory as appearing in the system profiler. How can I tell if there are actually 4gbs installed and the os is only addressing 3 of them without opening it up? From activity monitor it shows only 3gbs of memory, so I guess it is indeed just 3 of them there. From what I read if you put in 4gbs of ram system profiler might only show up 3 but the system actually DOES address all 4 of them, can someone verify this? Thanks.