Difference between 11i and R12 :

                       

you can find below difference in 11i and r12 architecture:

1) in 11i , we have 3 top level dir (appl/ comn /ora) where as in R12, one extra top (INST) is present which contains all configuration file  in it.
2) jserv in 11i replaced by OC4J.
3) forms and report version in 11i is 6i where as 10gAs in R12.
4) in 11i ------- 3 oracle _home (  9i rdbms , 6i O_H  and iAS O_H)
in R12 -------------- 10.1.2 (forms OH),  10.1.3 (OC4J  OH) and  10g  rdbms OH

5) mod_plsql   is not present in r12