Conversational Monitor System

Simple interactive single-user operating system.

- Conversational Monitor System

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Virtual machine

Virtualization/emulation of a computer system.

Logical diagram of full virtualization

IBM's CP/CMS, the first systems to allow full virtualization, implemented time sharing by providing each user with a single-user operating system, the Conversational Monitor System (CMS).

VM (operating system)

Family of IBM virtual machine operating systems used on IBM mainframes System/370, System/390, zSeries, System z and compatible systems, including the Hercules emulator for personal computers.

Teddy bear – VM's mascot since 1983.
The default login screen on VM/370 Release 6.
CMS starting up after the user MAINT (system administrator) has logged in.
The CMS editor on VM/370, editing a COBOL program source file.
Invoking the System/360 COBOL compiler on VM/370 CMS, then loading and running the program.
An example of a non-CMS guest operating system running under VM/370: DOS/VS Release 34. The DOS/VS system is now prompting the operator to enter a supervisor name to continue loading.
OS/VS1 starting under VM/370.
Using DASD Dump/Restore (DDR) to back up a VM/370 system.

CMS (Conversational Monitor System, renamed from the Cambridge Monitor System of CP/CMS). Most virtual machines run CMS, a lightweight, single-user operating system. Its interactive environment is comparable to that of a single-user PC, including a file system, programming services, device access, and command-line processing. (While an earlier version of CMS was uncharitably described as "CP/M on a mainframe", the comparison is an anachronism; the author of CP/M, Gary Kildall, was an experienced CMS user.)

IBM mainframe

IBM mainframes are large computer systems produced by IBM since 1952.

IBM 704 mainframe at NACA in 1957
IBM 1401 undergoing restoration at the Computer History Museum
IBM System/360 Model 50
IBM System z800

The virtual memory capabilities also allowed the system to support virtual machines; the VM/370 hypervisor would run one or more virtual machines running either standard System/360 or System/370 operating systems or the single-user Conversational Monitor System (CMS).

APL (programming language)

Programming language developed in the 1960s by Kenneth E. Iverson.

IBM typeballs and typewheel containing APL Greek characters.
A programmer's view of the IBM 2741 keyboard layout with the APL typing element print head inserted
British APL Association (BAPLA) conference laptop bag.

In the 1980s, the VSAPL program product enjoyed wide use with Conversational Monitor System (CMS), Time Sharing Option (TSO), VSPC, MUSIC/SP, and CICS users.

IBM 3270

Family of block oriented display and printer computer terminals introduced by IBM in 1971 and normally used to communicate with IBM mainframes.

IBM 3277 Model 2
Sample IBM 3270 cluster with one control unit connected to a printer and two displays
IBM selector-pen in use
3278 terminal
IBM 3279 Color Display Terminal
An Informatics General computer programmer using an IBM 3279 terminal
IBM 3290
4224 printer
IBM 3174 controller
IBM 3274-41D controller with terminal

Conversational Monitor System (CMS) in VM has support for the 3270 continuing to z/VM.

SAS (software)

Statistical software suite developed by SAS Institute for data management, advanced analytics, multivariate analysis, business intelligence, criminal investigation, and predictive analytics.

SAS Studio V on SAS Viya

In 1979, SAS 79 added support for the CMS operating system and introduced the DATASETS procedure.


Discontinued time-sharing operating system of the late 1960s and early 1970s, known for its excellent performance and advanced features.

CMS, the Cambridge Monitor System (and also Console Monitor System – but renamed Conversational Monitor System in VM) was a lightweight single-user operating system, for interactive time-sharing use. By running many copies of CMS in CP's virtual machines – instead of multiple copies of large, traditional multi-tasking OS – the overhead per user was less. This allowed a great number of simultaneous users to share a single S/360.


Research precursor to CP-67, which in turn was part of IBM's then-revolutionary CP[-67]/CMS – a virtual machine/virtual memory time-sharing operating system for the IBM System/360 Model 67, and the parent of IBM's VM family.

CP-40 ran multiple instances of client operating systems – particularly CMS, the Cambridge Monitor System, built as part of the same effort.

IBM OfficeVision

OfficeVision was an IBM proprietary office support application that primarily ran on IBM's VM operating system and its user interface CMS.


Imperative computer programming language, a dialect of ALGOL 68, that was developed by Stephen R. Bourne and Michael Guy to program the Cambridge Algebra System .

Computer memory map

Aside from the CAP computer, the compiler was ported to systems including Conversational Monitor System (CMS), TOPS-10, and Zilog Z80.