IBM Type-III Library (free in source code form at no charge to IBM customers, without support)
CP/CMS (Control Program/Cambridge Monitor System) is a discontinued time-sharingoperating system of the late 1960s and early 1970s. It is known for its excellent performance and advanced features.[1][2] Among its three versions, CP-40/CMS was an important 'one-off' research system that established the CP/CMS virtual machine architecture. It was followed by CP-67/CMS, a reimplementation of CP-40/CMS for the IBM System/360-67, and the primary focus of this article. Finally, CP-370/CMS was a reimplementation of CP-67/CMS for the System/370. While it was never released as such, it became the foundation of IBM's VM/370 operating system, announced in 1972.
Each implementation was a substantial redesign of its predecessor and an evolutionary step forward. CP-67/CMS was the first widely available virtual machine architecture. IBM pioneered this idea with its research systems M44/44X (which used partial virtualization) and CP-40 (which used full virtualization).
In addition to its role as the predecessor of the VM family, CP/CMS played an important role in the development of operating system (OS) theory, the design of IBM's System/370, the time-sharing industry, and the creation of a self-supporting user community that anticipated today's free software movement.
Fundamental CP/CMS architectural and strategic parameters were established in CP-40, which began production use at IBM's Cambridge Scientific Center in early 1967. This effort occurred in a complex political and technical milieu, discussed at some length and supported by first-hand quotes in the Wikipedia article History of CP/CMS.
In a nutshell:
In the early 1960s, IBM sought to maintain dominance over scientific computing, where time-sharing efforts such as CTSS and MIT's Project MAC gained focus. But IBM had committed to a huge project, the System/360, which took the company in a different direction.
The time-sharing community was disappointed with the S/360's lack of time-sharing capabilities. This led to key IBM sales losses at Project MAC and Bell Laboratories. IBM's Cambridge Scientific Center (CSC), originally established to support Project MAC, began an effort to regain IBM's credibility in time-sharing, by building a time-sharing operating system for the S/360. This system would eventually become CP/CMS. In the same spirit, IBM designed and released a S/360 model with time-sharing features, the IBM System/360-67, and a time-sharing operating system, TSS/360. TSS failed; but the 360-67 and CP/CMS succeeded, despite internal political battles over time-sharing, and concerted efforts at IBM to scrap the CP/CMS effort[citation needed].
In 1967, CP/CMS production use began, first on CSC's CP-40, then later on CP-67 at Lincoln Laboratories and other sites. It was made available via the IBM Type-III Library in 1968. By 1972, CP/CMS had gone through several releases; it was a robust, stable system running on 44 systems; it could support 60 timesharing users on a S/360-67; and at least two commercial timesharing vendors (National CSS and IDC) were reselling S/360-67 time using CP/CMS technology.
In 1972, IBM announced the addition of virtual memory to the S/370 series, along with the VM/370 operating system, a reimplementation of CP/CMS for the S/370. This marked the end of CP/CMS releases, although the system continued its independent existence for some time. VM releases continued to include source code for some time and members of the VM community long remained active contributors.
CP/CMS was built by IBM's Cambridge Scientific Center (CSC), a research and development lab with ties to MIT, under the leadership of Robert Creasy. The system's goals, development process, release, and legacy of breakthrough technology, set this system apart from other operating systems of its day and from other large IBM projects. It was an open-source system, made available in source code form to all IBM customers at no charge – as part of the unsupported IBM Type-III Library. CP/CMS users supported themselves and each other. Unusual circumstances, described in the History section below, led to this situation.
CP/CMS consisted of two main components:
CP, the Control Program, created the virtual machine environment. The widely used version was CP-67, ran on the S/360-67. (The research system CP-40 established the architecture. A third version, CP-370, became VM/370.) Instead of explicitly dividing up memory and other resources among users, which had been the traditional approach, CP provided each user with a simulated stand-alone System/360 computer. Each system was able to run any S/360 software that ran on the bare machine and in effect gave each user a private computer system.
CMS, the Cambridge Monitor System (and also Console Monitor System[3]– 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.
The CP/CMS virtual machine concept was an important step forward in operating system design.
By isolating users from each other, CP/CMS greatly improved system reliability and security.
By simulating a full, stand-alone computer for each user, CP/CMS could run any S/360 software in a time-sharing environment, not just applications specifically designed for time-sharing.
By using lightweight CMS as the primary user interface, CP/CMS achieved unprecedented time-sharing performance. In addition, the simplicity of CMS made it easier to implement user interface enhancements than in traditional OS.
IBM reimplemented CP/CMS as its VM/370 product line, released in 1972 when virtual memory was added to the S/370 series. VM/370's successors (such as z/VM) remain in wide use today. (IBM reimplemented CP-67, as it had CP-40, and did not simply rename and repackage it. VM coexisted with CP/CMS and its successors for many years. It is thus appropriate to view CP/CMS as an independent OS, distinct from the VM family.)
CP/CMS as free software
CP/CMS was distributed in source code form, and many CP/CMS users were actively involved in studying and modifying that source code. Such direct user involvement with a vendor-supplied operating system was unusual.
In the CP/CMS era, many vendors distributed operating systems in machine-readable source code[clarification needed]. IBM provided optional source code for, e.g., OS/360, DOS/360, and several later mainstream IBM operating systems. With all these systems, some awareness of system source code was also involved in the SYSGEN process, comparable to a kernel build in modern systems also in installing a Starter Set. (Forty years later, the Hercules emulator can be used to run fossilized versions of these systems, based on source code that is now treated as part of the public domain.)
The importance of operating system source code has changed over time. Before IBM unbundled software from hardware in 1969, the OS (and most other software) was included in the cost of the hardware. Each vendor had complete responsibility for the entire system, hardware and software. This made the distribution medium relatively unimportant. After IBM's unbundling, OS software was delivered as IBM System Control Program software IBM System Control Program (SCP) software, eventually in object code only (OCO) form.
For complicated reasons, CP/CMS was not released in the normal way. It was not supported by IBM, but was made part of the unsupported IBM Type-III Library, a collection of software contributions from IBM staff members (similarly software contributed by customers formed the Type-IV Library). IBM distributed this library to its customers for use 'as is'. The lack of direct IBM support for such products forced active users to support themselves and encouraged modifications and mutual support. CP/CMS and other Type-III products were early forms of free software.
Source code distribution of other IBM operating systems may have continued for some time (e.g. OS/360, DOS/360, DOS/VSE, MVS, and even TSS/370, which all today are generally considered to be in the public domain) since they were arguably published without a copyright notice before 1978.[4][5][This quote needs a citation]} However, the unsupported status of CP/CMS placed different pressures on its user community and created the need for source code distribution.
CP/CMS was contributed to the Type-III Library by MIT's Lincoln Laboratory and not by IBM, despite the fact that the system was built by IBM's Cambridge Scientific Center. This decision has been described as a form of collusion to outmaneuver the IBM political forces opposed to time-sharing[citation needed]. It is thought that it may also reflect the amount of formal and informal input from MIT and Union Carbide that contributed to the design and implementation of CP-40, the S/360-67, CP-67, and CMS. See History of CP/CMS (historical notes) for further insights and references on this topic.
Many CP/CMS users made extensive modifications to their own copies of the source code. Much of this work was shared among sites, and important changes found their way back into the core system. Other users, such as National CSS and some academic sites, continued independent development of CP/CMS, rather than switching to VM/370 when it became available. These efforts diverged from the community, in what today would be termed a software fork.
After IBM released VM/370, source code distribution of VM continued for several releases. (The VM project did not adopt the use of PL/S, an internal systems programming language mandated for use within IBM on many comparable projects. The use of PL/S would have made source code distribution impossible. IBM attempted to turn away from assembly language to higher level languages as early as 1965, and was making substantial use of PL/S by 1969, e.g. in MVS. PL/S was considered a trade secret at the time and was not available to customers. IBM apparently made exceptions to this policy much later.[6][7]) The VM user community continued to make important contributions to the software, as it had during the CP/CMS Type-III period. Few OS or DOS sites exhibited active user involvement in deep operating system internals, but this was found at many VM sites. This reverse support helped CP/CMS concepts survive and evolve, despite VM's second class citizen status at IBM.
Segregation of privileged "supervisor state" instructions from normal "problem state" instructions
Address translation hardware
When a program was running in "problem state," using a privileged instruction or an invalid memory address would cause the hardware to raise an exception condition. By trapping these conditions, CP could simulate the appropriate behavior, e.g. performing I/O or paging operations. A guest operating system, which would run in "supervisor state" on a bare machine, was run in "problem state" under CP.
The result was a fully virtualized environment. Each virtual machine had its own set of virtual devices, mapped from the system's real hardware environment. Thus a given dial-up teletype was presented to its VM instance as its virtual console.
Note that, in CP-67, certain model-dependent and diagnostic instructions were not virtualized, notably the DIAG instruction. Ultimately, in later development at IBM and elsewhere, DIAG instructions were used to create a non-virtualized interface, to what became called a hypervisor. Client operating systems could use this mechanism to communicate directly with the control program; this offered dramatic performance improvements.
Any S/360 operating system could in fact be run under CP, but normal users ran Cambridge Monitor System (CMS), a simple, single-user operating system. CMS allowed users to run programs and manage their virtual devices. CP-67 versions 1 and 2 did not support virtual memory inside a virtual machine. This was added in version 3. At that point, testing and development of CP itself could be done by running a full copy of CP/CMS inside a single virtual machine. Some CP/CMS operating system work, such as CP-370 development and MVS testing, ran four- or five-level deep stacks of hardware and OS simulations.
The CP/CMS design is different from IBM's previous monolithic operating systems, it separates complex "big system" (dispatching, hardware management, mass storage) from "little system" (application program execution, file I/O, console input/output). The re-categorization of both systems into their own entities prevents a bug in one users' system from affecting both. This is a model feature in microkernel operating systems.
IBM's decision to implement virtualization and virtual memory features in the subsequent S/370 design (although missing from the initial S/370 series) reflects, at least in part, the success of the CP/CMS approach. In turn the survival and success of IBM's VM operating system family, and of virtualization technology in general, owe much to the S/360-67.
CP: Control Program. CP-40 and CP-67 were implementations for CSC's customized S/360-40 and the standard S/360-67, respectively.
CMS: Cambridge Monitor System. This portion of the CP/CMS system was renamed Conversational Monitor System when IBM released VM/370. Unlike the CP-to-VM transition, however, which was a reimplementation, much of CMS was moved without modification from CP/CMS into VM/370.
VM: Virtual Machine, initially the term pseudo-machine was used, but soon virtual machine was borrowed from the IBM M44/44X project. It was well established in CP/CMS by the time IBM introduced VM/370.
hypervisor: a mechanism for paravirtualization. This term was coined in IBM's reimplementation of CP-67 as VM/370.
↑ Creasy, op. cit., p. 488 – "Console Monitor System"
↑ cf. Hercules emulator, which is apparently used to run these historic systems without raising complaints from IBM; the systems were published by IBM as machine readable source code and as microfiche
↑ public domain: "Until the Berne Convention Implementation Act of 1988, the lack of a proper copyright notice would force an otherwise copyrightable work into the public domain...."
↑ Pugh et al., p. 737, note 166 – citing the C. H. Reynolds August 1965 PL/I policy statement mandating use of PL/I
↑ W. R. Brittenham, The development of PL/S, IBM Technical Report (1974) – cited in Pugh
E.W. Pugh, L.R. Johnson, and John H. Palmer, IBM's 360 and early 370 systems, MIT Press, Cambridge MA and London, ISBN0-262-16123-0 ― extensive (819pp.) treatment of IBM's offerings during this period; the limited coverage of CP/CMS in such a definitive work is telling
R. J. Adair, R. U. Bayles, L. W. Comeau and R. J. Creasy, A Virtual Machine System for the 360/40, IBM Corporation, Cambridge Scientific Center Report No. 320‐2007 (May 1966) ― a seminal paper describing implementation of the virtual machine concept, with descriptions of the customized CSC S/360-40 and the CP-40 design
International Business Machines Corporation, CP-67/CMS, Program 360D-05.2.005, IBM Program Information Department (June 1969) ― IBM's reference manual
R. A. Meyer and L. H. Seawright, "A virtual machine time-sharing system," IBM Systems Journal, Vol. 9, No. 3, pp. 199–218 (September 1970) ― describes the CP-67/CMS system, outlining features and applications
R. P. Parmelee, T. I. Peterson, C. C. Tillman, and D. J. Hatfield, "Virtual storage and virtual machine concepts," IBM Systems Journal, Vol. 11, No. 2 (June 1972)
Background CP/CMS sources
F. J. Corbató, et al., The Compatible Time-Sharing System, A Programmer’s Guide, M.I.T. Press, 1963
F. J. Corbató, M. Merwin-Daggett, and R. C. Daley, "An Experimental Time-sharing System," Proc. Spring Joint Computer Conference (AFIPS) 21, pp. 335–44 (1962) — description of CTSS
F. J. Corbató and V. A. Vyssotsky, "Introduction and Overview of the MULTICS System", Proc. Fall Joint Computer Conference (AFIPS) 27, pp. 185–96 (1965)
P. J. Denning, "Virtual Memory", Computing Surveys Vol. 2, pp. 153–89 (1970)
J. B. Dennis, "Segmentation and the Design of Multi-Programmed Computer Systems," JACM Vol. 12, pp. 589–602 (1965) ― virtual memory requirements for Project MAC, destined for GE 645
C. A. R. Hoare and R. H. Perrott, Eds., Operating Systems Techniques, Academic Press, Inc., New York (1972)
T. Kilburn, D. B. G. Edwards, M. J. Lanigan, and F. H. Sumner, "One-Level Storage System", IRE Trans. Electron. Computers EC-11, pp. 223–35 (1962) ― Manchester/Ferranti Atlas
R. P. Parmelee, T. I. Peterson, C. C. Tillman, and D. J. Hatfield, "Virtual Storage and Virtual Machine Concepts", IBM Systems Journal, Vol. 11, pp. 99–130 (1972)
IBM mainframes are large computer systems produced by IBM since 1952. During the 1960s and 1970s, IBM dominated the computer market with the 7000 series and the later System/360, followed by the System/370. Current mainframe computers in IBM's line of business computers are developments of the basic design of the System/360.
In computing, a virtual machine (VM) is the virtualization or emulation of a computer system. Virtual machines are based on computer architectures and provide the functionality of a physical computer. Their implementations may involve specialized hardware, software, or a combination of the two. Virtual machines differ and are organized by their function, shown here:
Computer operating systems (OSes) provide a set of functions needed and used by most application programs on a computer, and the links needed to control and synchronize computer hardware. On the first computers, with no operating system, every program needed the full hardware specification to run correctly and perform standard tasks, and its own drivers for peripheral devices like printers and punched paper card readers. The growing complexity of hardware and application programs eventually made operating systems a necessity for everyday use.
The Conversational Monitor System is a simple interactive single-user operating system. CMS was originally developed as part of IBM's CP/CMS operating system, which went into production use in 1967. CMS is part of IBM's VM family, which runs on IBM mainframe computers. VM was first announced in 1972, and is still in use today as z/VM.
VM is a 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.
CP-67 is a hypervisor, or Virtual Machine Monitor, from IBM for its System/360 Model 67 computer.
z/VM is the current version in IBM's VM family of virtual machine operating systems. z/VM was first released in October 2000 and remains in active use and development as of 2022. It is directly based on technology and concepts dating back to the 1960s, with IBM's CP/CMS on the IBM System/360-67. z/VM runs on IBM's IBM Z family of computers. It can be used to support large numbers (thousands) of Linux virtual machines.
A hypervisor, also known as a virtual machine monitor (VMM) or virtualizer, is a type of computer software, firmware or hardware that creates and runs virtual machines. A computer on which a hypervisor runs one or more virtual machines is called a host machine, and each virtual machine is called a guest machine. The hypervisor presents the guest operating systems with a virtual operating platform and manages the execution of the guest operating systems. Unlike an emulator, the guest executes most instructions on the native hardware. Multiple instances of a variety of operating systems may share the virtualized hardware resources: for example, Linux, Windows, and macOS instances can all run on a single physical x86 machine. This contrasts with operating-system–level virtualization, where all instances must share a single kernel, though the guest operating systems can differ in user space, such as different Linux distributions with the same kernel.
SCRIPT, any of a series of text markup languages starting with Script under Control Program-67/Cambridge Monitor System (CP-67/CMS) and Script/370 under Virtual Machine Facility/370 (VM/370) and the Time Sharing Option (TSO) of OS/VS2; the current version, SCRIPT/VS, is part of IBM's Document Composition Facility (DCF) for IBM z/VM and z/OS systems. SCRIPT was developed for CP-67/CMS by Stuart Madnick at MIT, succeeding CTSS RUNOFF.
VP/CSS was a time-sharing operating system developed by National CSS. It began life in 1968 as a copy of IBM's CP/CMS, which at the time was distributed to IBM customers at no charge, in source code form, without support, as part of the IBM Type-III Library. Through extensive in-house development, in what today would be termed a software fork, National CSS took VP/CSS in a different direction from CP/CMS. Although the two systems would eventually share many capabilities, their technical implementations diverged in substantive ways.
The IBM Time Sharing System TSS/360 is a discontinued early time-sharing operating system designed exclusively for a special model of the System/360 line of mainframes, the Model 67. Made available on a trial basis to a limited set of customers in 1967, it was never officially released as a supported product by IBM. TSS pioneered a number of novel features, some of which later appeared in more popular systems such as MVS. TSS was migrated to System/370 and 303x systems, but despite its many advances and novel capabilities, TSS failed to meet expectations and was eventually canceled. The Resident Supervisor of TSS/370 was used as the basis for a port of UNIX to the IBM mainframe. TSS/360 also inspired the development of the TSS/8 operating system.
In computing, virtualization is the use of a computer to simulate another computer. The following is a chronological list of virtualization technologies.
CP-40 was a 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. Like CP-67, CP-40 and the first version of CMS were developed by IBM's Cambridge Scientific Center (CSC) staff, working closely with MIT researchers at Project MAC and Lincoln Laboratory. CP-40/CMS production use began in January 1967. CP-40 ran on a unique, specially modified IBM System/360 Model 40.
The IBM System/360 Model 67 (S/360-67) was an important IBM mainframe model in the late 1960s. Unlike the rest of the S/360 series, it included features to facilitate time-sharing applications, notably a Dynamic Address Translation unit, the "DAT box", to support virtual memory, 32-bit addressing and the 2846 Channel Controller to allow sharing channels between processors. The S/360-67 was otherwise compatible with the rest of the S/360 series.
This article covers the History of CP/CMS — the historical context in which the IBM time-sharing virtual machine operating system was built.
Operating System/Virtual Storage 1, or OS/VS1, is a discontinued IBM mainframe computer operating system designed to be run on IBM System/370 hardware. It was the successor to the Multiprogramming with a Fixed number of Tasks (MFT) option of System/360's operating system OS/360. OS/VS1, in comparison to its predecessor, supported virtual memory. OS/VS1 was generally available during the 1970s and 1980s, and it is no longer supported by IBM.
The history of IBM mainframe operating systems is significant within the history of mainframe operating systems, because of IBM's long-standing position as the world's largest hardware supplier of mainframe computers. IBM mainframes run operating systems supplied by IBM and by third parties.
Robert Jay Creasy 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.
A system virtual machine is a virtual machine (VM) that provides a complete system platform and supports the execution of a complete operating system (OS). These usually emulate an existing architecture, and are built with the purpose of either providing a platform to run programs where the real hardware is not available for use, or of having multiple instances of virtual machines leading to more efficient use of computing resources, both in terms of energy consumption and cost effectiveness, or both. A VM was originally defined by Popek and Goldberg as "an efficient, isolated duplicate of a real machine".
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
