As you can see in above tree structure, we have db, apps and inst as top level dir's
Under DB we have tech_st which is DB home and apps_st which holds DB datafiles.
Under apps, again we have tech_st which holds 1012 and 1013 homes, and apps_st holds APPL_TOP and OAD_TOP.
And finally inst which mainly stores instance specific files including runtime files, log files and configuration files
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