Channel-to-channel adapter

Virtual channel-to-channel adapters (VCTCA) are often used to communicate between two virtual machines in the z/VM operating system. The Virtual Machine Communication Facility (VMCF), and later Inter User Communication Vehicle (IUCV) are now often used in place of VCTCAs because they provide a simpler interface and improved performance.

I/O virtualization

According to a survey, 75% of virtualized servers require 7 or more I/O connections per device, and are likely to require more frequent I/O reconfigurations. In virtualized data centers, I/O performance problems are caused by running numerous virtual machines (VMs) on one server. In early server virtualization implementations, the number of virtual machines per server was typically limited to six or less. But it was found that it could safely run seven or more applications per server, often using 80 percent of total server capacity, an improvement over the average 5 to 15 percent utilized with non-virtualized servers.

Binary translation

static recompilationdynamic binary translatorDynamic Binary Translation
Virtual machine. Comparison of platform virtualization software. Shadow memory.


VPS/VM (Virtual Processing System/Virtual Machine) was an operating system that ran on IBM System/370 – IBM 3090 computers at Boston University in general use from 1977 to around 1990, and in limited use until at least 1993. During the 1980s VPS/VM was the main operating system of Boston University and often ran up to 250 users at a time when rival VM/CMS computing systems could only run 120 or so users. Each user ran in a Virtual Machine under VM, an IBM hypervisor operating system. VM provided the virtual IBM 370 machine which the VPS operating system ran under. The VM code was modified to allow all the VPS virtual machines to share pages of storage with read and write access.


For example, a computer that is running Microsoft Windows may host a virtual machine that looks like a computer with the Ubuntu Linux operating system; Ubuntu-based software can be run on the virtual machine. In hardware virtualization, the host machine is the machine which is used by the virtualization and the guest machine is the virtual machine. The words host and guest are used to distinguish the software that runs on the physical machine from the software that runs on the virtual machine. The software or firmware that creates a virtual machine on the host hardware is called a hypervisor or virtual machine monitor.

History of IBM mainframe operating systems

FORTRAN Monitor Systemdistant descendantsFMS
IBM has released several MVS upgrades: MVS/SE, MVS/SP Version 1, MVS/XA (1981), MVS/ESA (1985), OS/390 (1996) and currently z/OS (2001). VM/370 combined a virtual machine facility with a single-user system called Conversational Monitor System (CMS); this combination provided time-sharing by allowing each user to run a copy of CMS on his / her own virtual machine. This combination was a direct descendant of CP/CMS. The virtual machine facility was often used for testing new software while normal production work continued on another virtual machine, and the CMS timesharing system was widely used for program development.

Robert Creasy

Bob CreasyR. J. Creasy
Robert Jay Creasy (November 15, 1939 – August 11, 2005) was the project leader of the first full virtualization hypervisor, the IBM CP-40, which later developed into IBM's highly successful line of mainframe VM operating systems. Robert J. Creasy was born on November 15, 1939, in Honesdale, Pennsylvania. He graduated from MIT in 1961, marrying Rosalind Reeves that year. After graduation, he worked as a programmer on the CTSS timesharing system and on Project MAC.


CMS EXEC, or EXEC, is an interpreted, command procedure control, computer scripting language used by the CMS EXEC Processor supplied with the IBM Virtual Machine/Conversational Monitor System (VM/CMS) operating system. EXEC was written in 1966 by Stuart Madnick at MIT on the model of CTSS RUNCOM. He originally called this processor COMMAND, and it was later renamed EXEC. CMS EXEC has been superseded by EXEC 2 and REXX. All three — CMS EXEC, EXEC 2 and REXX — continue to be supported by the IBM CMS product. PROFILE EXEC is an EXEC that is automatically executed when a user logs on to tailor their environment.

Cross-platform software

Cross-platformPlatform independentmulti-platform
A notable exception to this is Java, which uses an operating system independent virtual machine for its compiled code, known in the world of Java as bytecode. Examples of software platforms are: As previously noted, the Java platform is an exception to the general rule that an operating system is a software platform. The Java language typically compiles to a virtual machine: a virtual CPU which runs all of the code that is written for the language. This enables the same executable binary to run on all systems that implement a Java Virtual Machine (JVM). Java programs can be executed natively using a Java processor. This isn't common and is mostly used for embedded systems.

List of operating systems

List of embedded operating systemsList of hobbyist operating systemsoperating system,
VM/370 (Virtual Machine / Conversational Monitor System, virtual memory operating system for System/370). VM/XA (VM/eXtended Architecture for System/370 with extended virtual memory). VM/ESA (Virtual Machine / Extended System Architecture, added 31-bit addressing to VM series). z/VM (z/Architecture version of the VM OS with 64-bit addressing). TPF Line (Transaction Processing Facility) on IBM S/360, S/370, and successor mainframes (largely used by airlines). ACP (Airline Control Program). TPF (Transaction Processing Facility). z/TPF (z/Architecture extension). Unix-like on IBM S/360, S/370, and successor mainframes. AIX/370 (IBM's Advanced Interactive eXecutive, a System V Unix version).

XB Machine

xB Machine has been a virtual operating system that was small enough to fit on a USB drive. The last version seems to have been in mid of 2008. It brought a secure computing environment that anonymized all internet activity, and had portable encrypted file storage. It had been developed and offered by XeroBank and based on a modified Gentoo Linux distribution. It could be executed as a virtual machine through a QEMU hypervisor, VMWare, VirtualBox, and any other major virtualization system. It could also be booted from on USB or burned to CD for booting.

Altor Networks

., a Juniper Networks Company, is a provider of security for virtual data centers and clouds. The company developed the world’s first firewall purpose-built for virtual networks, a software security "appliance" that runs in a virtualized environment and enforces security policy on a per-virtual-machine basis. Data center administrators could pinpoint a broad range of virtual network security comprises and create roles-based security policies. Security policies could be continuously enforced on individual virtual machines (VM), even as they moved throughout the virtualized data center.


VNETinternal IBM discussion group
VNET was first deployed as a private host to host network among CP/67 and VM/370 mainframes beginning before 1975. It was based on RSCS, a virtual machine–based communications program. RSCS used synchronous data link protocols, not SNA/SDLC, to support file to file transfer among virtual machine users. The first several nodes included Scientific Centers and Poughkeepsie, New York lab sites. RSCS-compatible communications code was subsequently developed for MVT/HASP, MVT/ASP and MVS mainframe operating systems. By September 1979, the network had grown to include 285 mainframe nodes in Europe, Asia, and North America.

TSS (operating system)

TSS/360TSS/370System/360 Model 67 Time Sharing System
It also implemented Virtual Memory and Virtual Machines using position-independent code. TSS/360 included an early implementation of a "Table Driven Scheduler" – a user-configured table whose columns were parameters such as current priority, working set size, and number of timeslices used to date. The kernel would refer to this table when calculating the new priority of a thread. This later appeared in systems as diverse as Honeywell CP-V and IBM z/OS. As was standard with operating system software at the time, TSS/360 customers (such as General Motors Research Laboratories) were given full access to the entire source of the operating system code and development tools.


They also have much in common with hypervisors, but the latter make no claim to minimality and are specialized to supporting virtual machines; indeed, the L4 microkernel frequently finds use in a hypervisor capacity. Early operating system kernels were rather small, partly because computer memory was limited. As the capability of computers grew, the number of devices the kernel had to control also grew. Throughout the early history of Unix, kernels were generally small, even though they contained various device drivers and file system implementations.

MTS system architecture

Branch on Program InterruptVirtual memory and Dynamic Address Translation (DAT)
In theory these virtual machines could be used to run any S/360 or S/370 system, but in practice the virtual machines were only used to debug MTS and so there may be subtle features that are not used by MTS that are not completely or correctly implemented. The MTS virtual machine was never updated to support the S/370-XA architecture (instead other tools such as SWAT and PEEK were used to debug MTS and IBM's VM/XA or VM/ESA were used to debug UMMPS). In the early 1970s work was done at Wayne State University to run a version of OS/MVT in a modified virtual machine (VOS) under MTS as a production service. "Student" virtual machines in MTS have also been created as teaching tools.

Michigan Terminal System

MTSMTS (Michigan Terminal System)University Computer Center
MTS can be IPL-ed under VM/370, and some MTS sites did so, but most ran MTS on native hardware without using a virtual machine. Some of the notable features of MTS include: The following are some of the notable programs developed for MTS: The following are some of the notable programs ported to MTS from other systems: MTS supports a rich set of programming languages, some developed for MTS and others ported from other systems: UMMPS, the supervisor, has complete control of the hardware and manages a collection of job programs. One of the job programs is MTS, the job program with which most users interact. MTS operates as a collection of command language subsystems (CLSs).

Cambridge Scientific Center

IBM's Cambridge Scientific CenterIBM Cambridge Scientific Center
Creasy, "A Virtual Machine System for the 360/40," IBM Corporation, Cambridge Scientific Center, Report No. 320-2007 (May 1966). R. A. Meyer and L. H. Seawright, "A Virtual Machine Timesharing System," IBM Systems Journal 9, No.3, 199-218 (1970). R. P. Parmelee, T. L. Peterson, C. C. Tillman, and D. J. Hatfield, "Virtual Storage and Virtual Machine Concepts," IBM Systems Journal 11, No.2, 99-130 (1972). E. C. Hendricks and T. C. Hartmann, "Evolution of a Virtual Machine Subsystem," IBM Systems Journal 18, No.1, 111-142 (1979). L. H. Holley, R. P. Parmelee, C. A. Salisbury, and D. N. Saul, "VM/370 Asymmetric Multiprocessing," IBM Systems Journal 18, No.1, 47-70 (1979). L. H. Seawright and R.


P5020NXP QorIQP1022
Features include 32/32 kB data/instruction L1 cache, 36-bit physical memory addressing [appended to the top of the virtual address in the process context, each process is still 32bit], a double precision floating point unit is present on some cores (not all) and support for virtualization through a hypervisor layer is present in products featuring the e500mc or the e5500. The dual and multi-core devices supports both symmetric and asymmetric multiprocessing, and can run multiple operating systems in parallel. The P1 series is tailored for gateways, Ethernet switches, wireless LAN access points, and general-purpose control applications.

Memory virtualization

Server virtualization, or Full virtualization, partitions a single physical server into multiple virtual machines, consolidating multiple instances of operating systems onto the same machine for the purpose of efficiency and flexibility. In both storage and server virtualization, the applications are unaware that the resources they are using are virtual rather than physical, so efficiency and flexibility are achieved without application changes.

History of operating systems

Historyhistory of mainframe operating systemsOperating systems
Operating systems originally ran directly on the hardware itself and provided services to applications, but with virtualization, the operating system itself runs under the control of a hypervisor, instead of being in direct control of the hardware. On mainframes IBM introduced the notion of a virtual machine in 1968 with CP/CMS on the IBM System/360 Model 67, and extended this later in 1972 with Virtual Machine Facility/370 (VM/370) on System/370. On x86-based personal computers, VMware popularized this technology with their 1999 product, VMware Workstation, and their 2001 VMware GSX Server and VMware ESX Server products.

Supervisory program

In the 1970s, IBM further abstracted the supervisor state from the hardware, resulting in a hypervisor that enabled full virtualization, i.e. the capacity to run multiple operating systems on the same machine totally independently from each other. Hence the first such system was called Virtual Machine or VM. *

Letter (alphabet)

Z, for example, is usually called zed in all English-speaking countries except the US, where it is named zee. As elements of alphabets, letters have prescribed orders, although this too may vary by language. In Spanish, for instance, ñ is a separate letter, sorted after n. In English, n and ñ are classified alike. Letters may also have a numerical or quantitative value. This applies to Roman numerals and the letters of other writing systems. In English, Arabic numerals are typically used instead of letters. Greek and Roman letters are used as mathematical symbols in equations and expressions.


ΖZeta (letter)ceda
[[Z|Z, z - Latin]]. З, з - Ze (Cyrillic). Allen, William Sidney. Vox Graeca: A guide to the pronunciation of Classical Greek. Cambridge: Cambridge University Press, 1987, pp. 56–59. Hinge, George. “Die Aussprache des griechischen Zeta”, in Die Sprache Alkmans: Textgeschichte und Sprachgeschichte. PhD dissertation. Aarhus: Aarhus University Press, 2001, pp. 212–234 =. Méndez Dosuna, Julián. “On for in Greek dialectal inscriptions”, Die Sprache 35 (1993): 82–114. Rohlfs, Gerhard. “Die Aussprache des z im Altgriechischen”, Das Altertum 8 (1962): 3–8. Teodorsson, Sven-Tage. “On the pronunciation of ancient greek zeta”, Lingua 47, no. 4 (April 1979): 323–32. Teodorsson, Sven-Tage.

English alphabet

modern English alphabetEnglishalphabet
Today, the English alphabet is considered to consist of the following 26 letters: indent=1 | A a B b C c D d E e F f G g H h I i J j K k L l M m N n O o P p Q q R r S s T t U u V v W w X x Y y Z z Written English has a number of digraphs, but they are not considered separate letters of the alphabet: indent=1 | ch ci ck gh ng ph qu rh sc sh th ti wh wr zh Outside of professional papers on specific subjects that traditionally use ligatures in loanwords, ligatures are seldom used in modern English.