Well, i know of at least one client that still has the binaries but not the sources of the cobol. But for the generic case, the mainframe is quite an integrate

Well, i know of at least one client that still has the binaries but not the sources of the cobol. But for the generic case, the mainframe is quite an integrated system, and big clients tend to use a lot of the features at the same time. Even if you can produce an executable or a library, but you ll still need a transaction manager (CICS/IMS-TM), a database (DB2/IMS), MQ, RACF, Datasets, GDG, REXX/JCL, etc. You need the whole ecosystem. And all the binaries will expect a DB2, or a MQ listening on the other side, with near-perfect emulation (return codes, db behaviour such as EBCDIC sorting, etc). Just compiling wont help you much unless you have a very basic use of mostly JCL and batches.