top output total sum of oracle processes RAM usage is more than actual physical RAM

redhat enterprise linux 4 U 4
two servers, each has 4GB RAM, shared storage, cluster oracle 10g rac database
when I look at top command output and sums up all the oracle processes RAM usage (i.e. the RES top field) the result is more then the actual physical RAM
this phenomena is on both servers
how can it be axplained ? how can I monitor the real RAM usage of oracle processes ?
Thnaks allot in advanced
eranpshAsked:
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mrjoltcolaCommented:
This is normal.

Oracle's SGA uses shared memory and is reported in each process size. The SGA is common to all Oracle server processes so for example a 1GB SGA x 8 processes will appear to be used 7GB more RAM than it really is.

Use ipcs command to see the segments
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