VMS also supports clustering? (called VAXcluster or later VMScluster), where multiple systems share processing, job queues, print queues, and disk storage, either over a special computer interconnect (CI) bus or over Ethernet (called a LAVC, for local area network VMS cluster).
VMS can be divided into three layers
DCL - Digital Command Language - command line interface
DECwindows - Digital's implementation of the X Window System
RMS - Record Management Services - high-level, language/device-independent IO
RTL - Runtime Libraries - shared routines and functions, callable from any language
VMS was originally developed by (project leader?) [Dave Cutler]?, who had earler developed Digital's RSX-11M operating system. Cutler was hired in 1988 by Microsoft to build the team that developed Windows NT.