2 IBM VM/370 eMS User's Guide

March 30, 1979
Section 1. What It Means To Have a eMS Virtual Machine Virtual Machine Facility/370 (VM/370) is a system control program that
controls "virtual machines." A virtual machine is the functional
equivalent of a real computer, but where the computer has "lights, buttons, and switches on the real console to control it, you control
your virtual machine from your terminal, using a command language of
active verbs and nouns. There are actually three command languages, CP, CMS, and RSCS. The command languages correspond roughly to the four components of VM/370: the control Program (CP), the Conversational Monitor System (CMS), the Remote Spooling Communications Subsystem (RSCS), and the
Interactive Problem Control System (IPCS). CP controls the resources of
the real machine; that is, the physical machine in your computer room; it also manages the communications among virtual machines, and between a
virtual machine and the real system. CMS is the conversational
operating system designed specifically to run under CPt it can simulate many of the functions of the OS and DOS operating systems, so that you
can run many OS and DOS programs in a conversational environment. RSCS is a subsystem designed to supervise transmission of files across a
teleprocessing network controlled by CP. IPCS provides system programmers and installation support personnel with problem reporting
and analysis functions. Its commands execute in the CMS command environment.
Although publication is concerned primarily with using CMS, it
also contains examples of CP commands that you, as a CMS user, should be
familiar with.
How You Communicate with VM/370 When you are running your virtual machine under VM/370, each command, or request for work, that you enter on your terminal is processed as it is
entered; usually, you enter one command at a time and commands are
processed in the order that you enter them. You can enter CP commands from either the CP or CMS environment; but
you cannot enter CMS commands while in the CP environment. The concept
of "environments" in VM/370 is discussed in "Section 2. VM/370 Environments and Mode Switching."
After you have typed or keyed in the line you wish to enter, you
press the Return or Enter key on the keyboard. When you press this key,
the line you have entered is passed to the command environment you want
to have process it. If you press this key without entering any data,
you have entered a "null line." Null lines sometlmes have special
meanings in VM/370. If you make a mistake entering a command line, VM/370 tells you what
your mistake was, and you must re-enter the entire command line. The
examples in this publication assume that the command lines are correctly
entered. You can enter commands using any combination of uppercase and
lowercase characters; VM/370 translates your input to uppercase.
Examples in this publication show all user-entered input lines in
lowercase characters and system responses in uppercase characters. Section 1. What it Means to Have a CMS virtual Machine 3