Oracle - how to know what internal executable or program performs DML (SELECT,UPDATE,INSERT,DELETE)? My goal is to bypass the query parsing when writing data (INSERT or UPDATE). Is it possible to use directly the executable beneath these commands?
No, it is effectively impossible. The RDBMS is simply too complicated. The block structure has been reversed engineered, but to even begin to do what the RDBMS itself does with those blocks is a gigantic task.

If your goal is to speed up INSERTs, then you can use an /*+APPEND*/ hint in some situations to speed things up, or use Data Pump to do the imports. 

Query parsing itself shouldn't really be a major overhead if your application is written properly and uses bind variables.

If you can be more specific about the performance problems you are seeing, and whether you're CPU or IO limited, we'll be able to help you.