In many cases only a recompile is necessary, although additional effort may be advisable for z/OS integration (such as SMP/E installation support).
Programs running under z/OS UNIX have full, secure access to the other internal functions of z/OS.
The file systems for z/OS UNIX (the older HFS[3][4] with DFSMS/MVS Version 1 Release 2[5] and the now preferred zFS), which support UNIX-style long filenames, appear as datasets[a] to the rest of z/OS.
z/OS UNIX's predecessor was an operating system component called OpenEdition MVS, first implemented in MVS/ESA SP 4.3 and enhanced in MVS/ESA 5.1.
OpenEdition MVS initially only supported the POSIX standards, but X/OPEN, the predecessor to The Open Group, certified MVS/ESA SP V5.1.