IBM Informix 64 bit ODBC connection

Creating a 64-bit ODBC connection for IBM Informix is a bit tricky. By default, only the 32-bit drivers are installed, so a x64 DSN cannot be created

1. Download the IBM Informix Client SDK from IBM Software Downloads
   At the time of writing, this is the version to get for Windows x64:
   Informix Client SDK Developer Edition for Windows x86_64, 64-bit, clientsdk.4.10.FC5DE.WIN.zip
   Note that you need to create a free IBM ID first.
2. Extract the zip to a folder
3. Right-click installclientsdk.exe and select Troubleshoot compatibility
4. Select Try recommended settings and select Start the program. The installation might progress slower then usual!
5. Step through the installer by clicking Next
6. At the production selection screen, deselect everything except:
1. IBM Informix ODBC Driver
2. Global Language Support (GLS)
7. Step through the installer by clicking Next until the end

Now a linked server can be created in SQL Server x64 that uses a DSN created with this driver.

Main tip from here: StackOverflow