Complex sentence: In MVS/370 and later incarnations of the OS, "branch entries" have replaced SVCs for invocations of many supervisory functions by so-called "authorized" programs and some supervisory functions may only be invoked by these "branch entries".
Split into simpler sentences: In MVS/370 and later incarnations of the OS, "branch entries" have largely replaced SVCs for invocations of these supervisory functions by so-called "authorized" programs. Indeed, some supervisory functions may only be invoked by these "branch entries".