CPU time reported on AWR

When I looked at the session of SQL stats in AWR report (Oracle 10g Release 2 Patch 1), the top SQL by Physical Reads lists the queries with large # of physical reads. I saw all the CPU time is only a small portion of elapsed time. I checked the waiting events and didn’t see these queries show up with long wait time. It leads me to believe that the Physical Read time is not part of the CPU time. When the logical reads occurs, it will take the CPU cycle which contribute to the total CPU time for the query. I could not find a proper document to discuss the detail of CPU time calculation. Any thought or related document will help me to understand the concept.

physical i/o is not cpu - it is i/o

Logical IO is CPU. Right?

correct, logical io comes from memory