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.