Question about ISAM reads vs output of onstat -u

Environment: Informix 7.31 S.O. HP-UX 11i The ISAM reads (output of onstat -g ppf) and disk reads are the same ? I followed the next steps: 1. session a: onstat -z 2. Session b: I run a query in dbaccess 3. Session a: onstat -g ppf | grep 0xb00091 (a particular table reads in the previous step) I see 159027 4. Session a: onstat -u (I see nreads = 0 for my user) Why ISAM reads (of onstat -g ppf) > 0 and nreads (of onstat -u) = 0 When the ISAM reads occur ? Thanks in advance