It would be better if you can tell us how you are coming to the conclusion that the RAM is 100% consumed? As 11g has mentioned, there may be cached portion of RAM which you would need to take into account.
How many instances and how many Oracle server processes?
If you do have 1029 processes, I'd expect at least a gig or two of memory consumed in addition to SGA and PGA. The latter may also be larger than target, maybe more probably so with many processes (at least "some" space for session etc. is required).