Browse Prior Art Database

Virtual Control Store for the VM/370 Virtual Machine: Version 2 Disclosure Number: IPCOM000148753D
Original Publication Date: 1978-May-16
Included in the Prior Art Database: 2007-Mar-30

Publishing Venue

Software Patent Institute

Related People

Attanasio, C.R.: AUTHOR [+2]


RC 7126 (#30501) 5/16/78 Computer Science 10 pages

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RC 7126 (#30501) 5/16/78

Computer Science 10 pages

V i r t u a l Control Store f o r the VM/370 V i r t u a l Machine: Version 2

C. R. Attanasio
IBM Thomas J. Watson Research Center
P. 0. Box 218 Yorktown Heights, N. Y. 10598

Abstract: This paper updates RC6327 t o describe Version 2 o f V i r t u a l C o n t r o l Store f o r t h e VM/370 v i r t u a l machine. The major extensions over t h e previous v e r s i o n are: support f o r d i s t i n c t input/output devices f o r t h e VCS domain, and t h e a b i l i t y t o map an a r b i t r a r y number o f v i r t u a l main s t o r e segments i n t o VCS.

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The VM/370 (1,2) virtual machine consists of a virtual cpu,
virtual main storage (VMS hereafter), and
a set of virtual
input/output devices. Its architecture is essentially that
of System/370, except that timing dependencies are not
preserved for the virtual machine, and the

instruction has been redefined to provide some additional
services for the virtual machine (3).

This paper describes the implementation of a second address
space (virtual control store or
VCS (4,511 for the virtual
mac h
i ne . VCS allows the implementation of additional
instructions for the VM/370 virtual machine, analogously to
the way in which (real) control store implements the
System/370 instruction set in many models of System/370.

Standard VMI370 consists of two protection domains. The
Control Program (CP) is the supervisor portion, executes
always with total capability (supervisor state and
protection key zero) and is essentially uninterruptable.
The user domain is his virtual machine; CP restricts the
virtual machine to its subset of real resources defined
administratively in the CP directory. Mithin his virtual
machine the user has total capability via CP commands which
simulate the operator's console, e.g., IPL, STORE, etc.

VCS provides an additional domain between CP and the virtual
machine. A new CP console command IMPL (Initial
Micro-Program Load, by analogy to the real machine) creates
VCS; the only valid argument of this command is
a named
system saved
by CP for use in VCS. All other CP console
functions are restricted to operate only on
VMS and its
associated registers and psw.
A s part of the execution of
IMPL, the program in
VCS is entered and performs
initialization functions, which may include verifying the
authorization of the user to use the selected system.

The VCS program implements an instruction whose operation
code is illegal
( i n the current implemen*tation) in the
absence of VCS. Thus the user accesses VCS only through a
well-defined instruction-level interface. When the VCS
program is interpreting this instruction for the
programs, one or more specified segments of VMS are mapped
into pre-defined segments of VCS.

To CP, VCS code has no pa...