waiting for harddisk

i am using postgresql 8.1.8,

Following configurations:
           shared_buffers = 5000
            work_mem = 65536
            maintenance_work_mem = 65536
            effective_cache_size = 16000
            random_page_cost = 0.1

The cpu is waiting percentage goes upto 50%, and query result comes later,

i am using normal select query ( select * from table_name ).

table has more then 6 million records.



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With Best Regards,
Petchimuthulingam S