Unlike many modern software packages, the Oracle ODBC driver installation is often a manual process involving the command line.
If you try to install the ODBC driver without the Instant Client present on your system path, the installation will likely fail, or the driver will not appear in your ODBC Data Source Administrator. oracle odbc download
Attempting to mix architectures (e.g., a 64-bit application trying to use a 32-bit driver) will result in a "Data source name not found and no default driver specified" error. Unlike many modern software packages, the Oracle ODBC