Here are the various types of ODBC Data Source Types:
1. System DSN: This is the DSN used throughout the system, any with proper rights may log in. This DSN must be created on the machine where the program is located. The System DSN are stored in the Windows registry under the following key: HKEY_LOCAL_MACHINE\Software\Odbc\Odbc.ini\Odbc Data sources
2. User DSN: This is a DSN created for a specific user. Only the user who created the DSN can see this and use it. Like the System DSN, the information is stored in the Windows registry under the following key: HKEY_CURRENT_USER\Software\Odbc\Odbc.ini\Odbc Data sources
3. File DSN: This is a DSN that is stored in a text file with a .DSN extension (not in the Windows registry). To use a File DSN, it must contain the information required to connect to the desired data source. The ODBC driver must be installed locally. The .dsn file is a text file that you can view in any text editor, such as Microsoft Notepad. The File DSNs are stored by default in the following location:Program Files\Common Files\Odbc\Data Sources folder.
Please see the Microsoft knowledge base article on File DSN: http://support.microsoft.com/kb/165866/en-us
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