Both CSDK version 3.50 and CSDK 3.70 are supported on Windows
7 operating system, which makes difficult to decide which one to use. A useful
way to decide which CSDK to use is:
consider what version of Informix Server you are using. By design, the CSDK version will be the "latest 3.x for 11.x". Here “x” is the same minor version number “.50” or .”70” as the database engine, e.g., Informix 11.50 and CSDK 3.50; or Informix 11.70 and CSDK 3.70.
In regard to the bit level, 64-bit windows will support either 32-bit ('.TC') or 64 bit (.'FC') CSDK. Although the bit level is not significant for determining which one to use, it is important to note that the ODBC manager on Windows 7 is 64-bit. If you want use a 64-bit CSDK, you will have no issues. However, a 32-bit CSDK will require an older ODBC manager.