z / VM

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z / VM
Basic data

developer IBM
Publishing year 2001
Current  version 6.4.0
(November 11, 2016)

z / VM is an operating system for z Systems . It is used to create, manage and run virtual machines on the mainframe in parallel. The ancestry of z / VM goes back to the CP / CMS of the 1960s via a first official publication for S / 370 in August 1972 . The hypervisor in z / VM is called Control Program (CP). It was the first implementation of virtual machines.

z / VM is suitable for a wide range of uses:

  • End users with a text-based workplace;
  • System developer with a wide range of development tools from assembler to high-level languages;
  • Service provider, since today's mainframe computers can provide a few hundred to a thousand virtual machines at the same time. With z / VM, (almost) any number of Linux instances can be operated on one mainframe.

Concept of VM

VM (an acronym for V irtual M achine) conceptually anticipated the concept of today's virtual machines as early as 1964 with a complete emulation of the hardware in this same VM (Varian). Any operating system can be emulated in a VM (at that time e.g. MVS , DOS / 360, UNIX ). Then as now, you could provide a personal computer (initially CMS) or a server (initially RSCS, VTAM / VSCS, TCP / IP , UNIX). Virtual communication could be mapped to real communication and thus enable real communication. When VMs should exchange information, virtual channels were switched. With the Hercules emulation , a 360/370/390 / z emulation can be installed on any Windows / Linux PC.

The CMS (Conversational Monitoring System) development system was included as standard in the delivery of the VM / 370 system. Most of the other systems (RSCS, VTAM / VSCS, SQL etc.) were licensed.

The development of VM in the academic environment brought competition to DOS / 360 (later also to OS / 360, which became MVS, the forerunner of z / OS, via OS / VS further development OS / VS2) and also led to it within IBM Competition in business with large customers, so that the concept of the virtual machine was not propagated by IBM.

VM and open source

VM was delivered completely in the source code (almost entirely assembler) until the mid-1980s. Significant parts of this system have also been adopted through community improvements. Until at least the late 1990s, nothing has changed, although a few parts of VM were not delivered more in the source code, which began with the components GCS ( G roup C ontrol S ystem) and VTAM ( V irtual T elecommunications A ccess M ethod) the part of VM required for IBM's SNA network architecture ( S ystems N etwork A rchitecture).

History of VM

  • around the end of 1950s to the early 1960s: The C ompatible T IME S haring S ystem (CTSS) is at MIT designed and implemented. The central computer could be operated interactively by several users ( time sharing ).
    At the time, this was in stark contrast to the so-called batch processing, in which a batch of punched cards with program instructions is handed over to the data center and, after they have been processed, the results - usually in long paper lists - are picked up again.
  • approx. 1965: The CTSS is rewritten for the IBM / 360 Model 40. The hypervisor for the control and provision of the virtual machines is separated from the interactively operated operating system of these virtual machines.
    The hypervisor was henceforth called CP (Control Program). The interactive operating system for the virtual machine was known as the CMS (Conversational Monitor System or Cambridge Monitor System).
  • approx. 1968: CP-67 is rewritten for the IBM / 360-67. At the time, VM is a product supported by IBM, but still based on the commitment of the University of Cambridge.
  • 1970/71: IBM uses VM as a development platform for OS / 370, since VM can display the IBM / 370 as an emulation on an IBM / 360. Since that time, VM has also been marketed by IBM, but never as a primary system, but always as a carrier system for other operating systems.
  • Up to approx. 1985: Conversion from teletype consoles to screen terminals, expansion of network capabilities, introduction of a fully programmable full-screen editor and a rudimentary menu support derived from it, introduction of the procedural languages ​​EXEC-2 and REXX, etc.
    Derivation of the "hardware-based" logical partitioning of mainframes from VM.
  • Until approx. 1990: Extensions to VM and the IBM / 370 with its successor IBM / 370-XA with the extension of 24-bit addresses to 31-bit addresses lead to mutually incompatible VM versions (VM / SP, VM / HPO and VM / XA).
    The 370 / ESA architecture becomes the successor to the entire IBM / 370 and IBM / 370-XA lines. VM undergoes a consolidation and general overhaul and becomes VM / ESA.
  • until approx. 2005: Further changes and extensions of the mainframe architecture to Series Z also require adjustments to VM, which becomes z / VM. Around 1998 an attempt was made - more out of arrogance than an economic vision - to get Linux to work under VM as well. That turned out to be unexpectedly easy and is now being marketed.

More information on CP and CMS

  • CP / Control Program provides virtual machines as a hypervisor program . It can only be controlled via a virtual machine. When they are defined, the virtual machines receive, among other things, certain rights vis-à-vis the CP. Due to the constructive properties of the IBM mainframe computers at the hardware level, these authorizations are practically impossible to circumvent.
  • CMS / Conversational Monitor System already had the following properties in the first implementation in the mid-1960s:
    • File names with 8-character file names and file types
    • So-called file modes from A to Z, each of which has a hard disk in direct access. These hard disks are referred to as MiniDisk under VM and are comparable to today's drive letters under PC operating systems.
    • A file system (OS / 360 and DOS, which were created at the same time for the mainframe, did not have something like this to this extent, where you had to allocate the disk space for files largely manually).
    • a line-oriented user interface on which teletyping consoles are used, e.g. B. IBM 3270 terminals - in contrast to the punch cards that were widely used until the 1980s.
    • In addition, the XEDIT editor had a very powerful system for tracking changes to program source texts as early as the 1970s.

More than 10 years later, the forerunners of today's PC operating systems adopted many of these concepts that are now taken for granted.

Performance and typical usage scenarios for VM

The typical usage of VM is

  • As an online system with e-mail and other information applications for up to several thousand users.
  • As a carrier system for online processing under z / VSE or z / OS with databases.
  • As a development and test system for VM itself, z / VSE , Linux for z Systems , z / OS and TPF .
  • As a carrier system for up to several thousand Linux servers on a single mainframe.
  • As an open source training system for programmers and computer scientists.

All of these application scenarios can also exist side by side for the same user. Here VM is very efficient in using the available resources. In particular, the provision of the virtual main memory can, from experience, easily be carried out up to eight times the actual memory. A value that can hardly be achieved by other systems in 2006 either.


Virtual Machine / 370
Virtual Machine / Extended Architecture
  • 1989: VM / XA SP R2.1
Virtual Machine / Enterprise Systems Architecture
  • 1990: VM / ESA Version 1 Release 1.0
  • March 19, 1991: VM / ESA Version 1 Release 1.1
  • June 16, 1992: VM / ESA Version 1 Release 2
  • May 20, 1993: VM / ESA Version 1 Release 2.1
  • April 6, 1994: VM / ESA Version 1 Release 2.2
  • June 12, 1995: VM / ESA Version 2 Release 1.0
z / VM
  • September 12, 2008: z / VM V5.4
  • October 23, 2010: z / VM V6.1
  • December 2, 2011: z / VM 6.2
  • July 26, 2013: z / VM 6.3
  • November 11, 2016: z / VM 6.4 (announced)

See also

Individual evidence

  1. ^ A b Bill Bitner, Susan Greenlee: z / VM - A Brief Review of Its 40 Year History. (PDF; 95 KB) IBM, 2012 .
  2. ^ Z / VM Withdrawal from Marketing - Announced Dates. IBM, July 23, 2013 .
  3. Control Program (CP). In: z / VM V6R3 Library. IBM, December 2015 .
  4. Melinda Varian: VM and the VM Community: Past, Present, and Future. (PDF; 183 KB) August 1997 .
  5. Entry VM and the VM Community: Past, Present, and Future, revised 08/16/97 (PDF; 127 kB)
  6. z / VM End of Service Effective Dates. Retrieved October 25, 2016 .
  7. ^ IBM United States Software Announcement 216-075. Retrieved October 25, 2016 .

Web links