One of the first decisions affecting the design of an APPC/MVS transaction is portability. If you want your transaction program to be able to run on other operating systems besides z/OS, you can use CPI Communications to make it more easily portable to other systems including AIX, OS/400, OS/2, and VM. APPC/MVS supports Common Programming Interface (CPI) Communications routines as documented in CPI-C Reference with deviations listed in Using CPI Communications of this document.

If you want your transaction program to be able to use specific features of MVS and provide them to transaction programs on other systems, the MVS TP conversation services might be more appropriate. For example, using MVS TP conversation services, an MVS transaction program can send data to a partner program from an MVS data space, and can specify asynchronous processing.

Both CPI Communications and MVS TP services support high-level languages including COBOL, C, FORTRAN, PL/I, and REXX. You can combine calls to CPI Communications and MVS-specific services in the same conversation from a TP written in one of those languages. Calls to the MVS-specific services will not change any CPI Communications conversation characteristics previously established by a CPI Communications call. Any combination of MVS-specific services with CPI Communications calls will affect portability, because the MVS services will not work on other systems.

One way to minimize their affect on portability is to call MVS-specific services from subroutines that can be bypassed in non-MVS environments.