Hi Vinod

This will happen only from Oracle8 onwards. The smaller value in shared pool is basically an array of pointers to each block in db_block buffers. This is also called as a buffer header. This can be calculated as show below

size of db_block_buffers in shared pool = db_block_buffer_parameter * (size_of_C_pointer + size_of_one_buffer_header)

the two parameters are o/s dependent

Santhosh kumar
Certified Oracle DBA - 8i