Hello Sir,
I have got the membership already and I would like to thanks you for such wonderful information. As I am going through the presentation one by one and having trouble installing the Oracle Release 12 on virtual system. I exactly follow the step carefully as you mentioned in your tutorial. But I got stuck during the installation, At one point of time it is asking me to enter the RDMS Disk4 location and their is no Disk 4 under /home/Oracle/stage/oraDb folder.

I checked couple of web site but really could n't get any help. I am really willing to follow your tutorial as you mention and don't want to use vision database. Please kindly asssit me to resolve this issue.

I know few people have complained about this error before as well. You can use the search feature of the forum.
This error usually occurs when your stage is not properly created. Oracle is not finding the files are the right location.
Verify that all necessary folders are there in your stage. Take a look at subfolders inside oraDB and verify if all is there. Also verify if the label file is there inside your oraDB folder and it has the right content.
Otherwise you will have to create the stage (start from recreating ISO).