In coexistence mode, you can run ICSF and PCF simultaneously on the same z/OS system and run a PCF application on PCF or on ICSF. A PCF application running on ICSF gains the enhanced performance, reliability, and availability of ICSF.
A PCF application running on ICSF can still use PCF macros, because ICSF supports these macros. ICSF ships changed PCF macros in SAMPLIB that run only on ICSF. Because these changed PCF macros already exist unchanged on PCF, the changed PCF macros shipped with ICSF are named differently.
You can rename these macros to the PCF names when you want to run a PCF application on ICSF.
Then the application can run only on ICSF. To run a PCF application on PCF, just run the application without reassembling the application.
During migration, you can start ICSF and start PCF so that both products are running simultaneously. If you want to run a PCF application using the PCF macros on PCF, do not reassemble the application. If you want to run a PCF application using the changed PCF macros on ICSF, reassemble the application against the changed macros. Coexistence mode enables you to run the products simultaneously and choose whether to run a PCF application on PCF or ICSF.
A PCF application can use keys on the PCF CKDS. When you run the application on ICSF, those keys must be in the ICSF CKDS. The format of a key entry on the PCF CKDS differs from the format of a key entry on the ICSF CKDS. Therefore, you need to run a conversion program to convert the PCF CKDS entries and place the entries in the ICSF CKDS. See Converting a PCF CKDS to ICSF format for a description of how to convert a PCF CKDS.
In coexistence mode, the safest method for changing the master key is to re-IPL the system. See Changing the DES master key in compatibility or coexistence mode for a description of the process used to change the master key in coexistence mode.