z/VM
Z / VM (formerly VM / CMS) is an operating system developed by IBM for mainframe systems. It serves an (almost ) to create any number of virtual machines on a mainframe computer system to manage and operate in parallel. z / VM has its roots back to the 1960s, the ancestor of the PC - based virtualization systems.
Z / VM is very well suited for a wide range of use:
- End users with a text- based work;
- System developers with a wide range of development tools from assembler to high-level languages ;
- Service providers, as today's mainframe can provide a few hundred to a thousand virtual machines simultaneously. Just under z / VM can ( almost) any number of Linux instances are operated on a mainframe one.
Concept of VM
VM ( an acronym for Virtual Machine) has been conceptually 1964 with a full emulation of the hardware in this same VM, the concept of today's virtual machines anticipated ( Varian). In a VM, any operating system to be emulated (then eg MVS, DOS/360, UNIX). They could then, as now, therefore, a personal computer ( first CMS) or a server (initially RSCS, VTAM / VSCS, TCP / IP, UNIX) provide. Virtual communication could be mapped to real communication, thus enabling real communication. If VMs should exchange information, virtual channels have been switched. With emulation Hercules a 360/370/390/z-Emulation on any Windows / Linux PC can be installed.
In the delivery of the system, the development system VM/370 CMS ( Conversational Monitoring System) was supplied as standard. Most of the other systems ( RSCS, VTAM / VSCS, SQL, etc ) were licensed.
The development of VM in an academic environment brought competition to the DOS/360 (later also to the OS/360 via the OS / VS development OS/VS2 to MVS, the forerunner of the z / OS was ) and has led to well within the IBM competition in business with major customers, so the concept of virtual machine is not propagated by IBM.
VM and open source
VM was until about the mid-1980s completely in the source code ( almost all assembler ) delivered. Significant parts of this system were also taken from improvements to the user community. Until at least the late 1990s has not changed, although a few parts were no longer delivered by VM in the source code, which began with the components of GCS ( Group Control System) and VTAM ( Virtual Telecommunications Access Method) of for IBM's Network Architecture SNA ( Systems Network Architecture ) required part of VM.
History of VM
- About the end of 1950s to the early 1960s: The Compatible Time - Sharing System ( CTSS ) is designed and implemented at MIT. The central computer was by multiple users interactively operated ( time-sharing ).
The time is in stark contrast to the so-called batch processing, in which a stack of punch cards you turn in with program instructions in the datacenter and the results after the execution of which - usually in long paper lists - pick up again.
- Ca 1965: The CTSS is rewritten for the IBM/360 Model 40. Here, the hypervisor for the management and delivery of virtual machines is separated from the interactive -use operating system that virtual machines.
The hypervisor was henceforth called CP (Control Program). The interactive operating system for the virtual machine is called CMS ( Conversational Monitor System or Cambridge Monitor System ).
- Ca 1968: CP -67 is rewritten for the IBM/360-67. VM at this time is a true of the IBM supported, but still based on the commitment of the University of Cambridge product.
- Ca 1970/71: IBM VM used as a development platform for OS/370 because VM can represent the IBM/370 as an emulation on a IBM/360. Since that time VM is also marketed by IBM, but at no time as the primary system, but only as a support system for other operating systems.
- Up to about 1985: Conversion of Telegraph consoles on display terminals, expansion of network capabilities, introduction of a fully programmable full-screen editor and a derived rudimentary menu support, the introduction of the procedure languages EXEC 2 and REXX, etc.
Derivation of " hardware-based " logical partitioning of mainframe computers from VM.
- Up to about 1990: Enhancements to VM and the IBM/370 with their successors IBM/370-XA with the extension of 24 -bit addresses to 31 -bit addresses result in mutually incompatible versions of VM ( VM / SP, VM / HPO and VM / XA).
The 370/ESA-Architektur is the successor of the total IBM/370- and IBM/370-XA-Linien. VM is subjected to a consolidation and overhaul and VM / ESA.
- Up to about 2005: Other changes and enhancements to the mainframe architecture to the Z series also require adjustments to VM, the z / VM. Around 1998 - Following more from arrogance than an economic vision - attempts to Linux under VM running. That turned out to be unexpectedly easy, and is now also marketed.
For more information on CP and CMS
- CP / Control Program provides as Hypervisorprogramm ready virtual machines. It is to control itself only on a virtual machine. The virtual machine is available from your definition include certain rights against the CP. Constructional features of the IBM mainframe at the hardware level these permissions are also virtually unavoidable.
- CMS / Conversational Monitor System had been in the first implementation in the mid-1960s following properties: File names with 8 - character file names and file types
- So-called file modes (File mode ) from A to Z, each of which maintains a disk in direct access. These disks are referred to below as VM minidisk and with today's drive letter using PC operating systems comparable.
- A file system ( OS/360 and DOS that emerged at the same time for the mainframe, had something not to this extent, there had to free disk space to files largely manually assign ).
- A line-oriented interface to the working over teletype consoles, such as the IBM 3270 terminals - in contrast to the highly popular until the 1980s punch cards.
- In addition, the editor XEDIT has already in the 1970s a very powerful system for tracking changes of program source code.
More than 10 years later, the forerunner of today's PC operating systems took many of these concepts that are now taken for granted.
Performance and typical usage scenarios for VM
The typical use of VM is
- As an online system with e-mail and other information appliances for up to several thousand users.
- As the support system for online processing on z / VSE or z / OS databases.
- As a development and test system for the VM itself, z / VSE, zLinux, z / OS and TPF.
- As a carrier system for up to several thousand Linux servers on a single mainframe computer.
- An open-source training system for programmers and computer scientists.
All of these application scenarios may also be present side by side with the same user. This VM is very efficient in the use of existing resources. Specifically, the provision of the virtual main memory can be easily driven from experience to eight times the existing real memory. One in 2006 hardly accessible by other systems value.