Originally posted by AJW_ID01
Is 25 a generically prudent choice?

If so, why on earth does it default to 100?
Yes, and "I have no idea".

Actually in 9i there is a functionality for collecting system (ie. hardware) statistics that supercedes this parameter (if they have been colected then this parameter is ignored). It's accessed by running the DBMS_STATS.GATHER_SYSTEM_STATS procedure which is documented in the Supplied packages book http://tahiti.oracle.com

All the same it's good to have a fallback value for that parameter, and 25 is pretty reasonable.