VSE originally supported 24-bit addressing; as the underlying hardware was extended it was also to progressively support 31-bit addressing.
The main interfaces to MVS are JCS (Job Control Statements), the [batch processing]? interface. There is also a special interface used by operators at the system console. CICS is an interface widely used for online applications.
VSE, like MVS systems, are traditionally accessed by [3270 terminals]?, or by PCs running 3270 emulators.