If you want a deeper understanding of how the buffer cache is being utilized, there are a few additional queries you can run to gain such insight.  If the keep and recycle buffer caches are being used, you can run the cacheobjcnt.sql  query to get an idea on how many objects have been assigned to each cache:

For the complete listing of the cacheobjcnt.sql  query, please refer to the online Code Depot at http://www.dba-oracle.com/bp/bp_book5_perf.htm.

This query looks at the sys.seg$ view and the output may resemble something like the following:

CACHE     OBJECTS

-----------------

default      2023

keep            5

Finally, you may wish to analyze the buffer cache activity from time to time to see how it is being utilized.  The buffutl.sql  script will show you how full the cache currently is along with the state of the buffers in the cache:

For the complete listing of the buffutl.sql  script, please refer to the online Code Depot at http://www.dba-oracle.com/bp/bp_book5_perf.htm.

This script queries the sys.x$bh, and sys.ts$ views and the output might look something like this:

BUFFER_STATE      AMT_KB

------------------------

being read          5920

free               23568

read/mod           47952

read/notmod            0

If you're a DBA who's looking for real world Oracle tuning techniques, Oracle scripts, and advice on how to get to the heart of critical Oracle performance problems, then you've come to the right place. Oracle Performance Troubleshooting: With Dictionary Internals SQL & Tuning Scripts was written by one the world's most widely-read DBAs and Oracle internals experts. Robin Schumacher focuses his incredible knowledge of the Oracle data dictionary into a superb book that shows how to quickly troubleshoot and correct Oracle performance problems. 

Plus! The online code depot is available immediately!

http://www.dba-oracle.com/bp/bp_book5_perf.htm