VME (Virtual Machine Environment) occurs as mainframe operating system developed by the UK company International Computers Ltd (ICL). Originally developed in the 1970s to drive ICL's (so) fresh 2900 series mainframes, the operating formulas is okay, called OpenVME, & diarrhea in ICL Series 39 & Trimetra mainframe.

ICL itself has been absorbed into a Fujitsu group.

Origins

VME wwhen foremost announced under a title VME/B as a operating body for the ICL Future Range of mainframes (2900 Series). The total of influences may be seen within its project, e.g. Multics and ICL's earlier George 3 operating system; but it was basically designed from either scratch. Virtually all of the project & development took place at ICL's facilities around Kidsgrove, Staffordshire and Manchester, UK. A primary designer was Brian Warboys. As a creation of the mid-1970s, by having there are no constraints to become compatible by using sooner operating systems, VME is around numerous ways extra modern inside its architecture than in todays world's Unix derivatives (Unix was designed in the 1960s) or Windows (which started as an operating patterns for lone-user computers, & however betrays victims origins).

Fallowing a cancellation of ICL's guide operating formulas VME/K in the early 1980s, VME/B was renamed as VME 2900. VME 2900 was presented to a client base as a merger of VME/B & VME/K, however actually the code was 100% VME/B, by having two or three selected features from either VME/K grafted in. A "2900" postfix wwhen dropped once ICL launched Series 39 as a successor to a original 2900 series; & the "Open" prefix was afterwards added once VME became capable of hosting applications written originally for Unix.

A virtually all recent incarnations of VME start as a hosted subsystem inside Windows in Intel-depending devices.

Architecture

VME is structured as a placed of shells, for each one layer getting access to resources at different levels of abstraction. Virtual resources provided by 1 layer come constructed from either a virtual resources offered per layer following. Access to the resources of both layer is controlled across the placed of Access Levels: sequentially for the run to utilize the resource at the particular access level, it must keep around an access key offering access thereto level. A construct is similar to the "rings of protection" in Multics. A architecture allows Sixteen access levels, of which a outer Sextet come reserved for user-level code.

Orthogonally to the access levels, the operating body makes resources available to applications in the form of a Virtual Machine. The Virtual Machine potty start multiple processes. Around practice, the VME Virtual Machine is nigher to the construct of the run in additional operating systems, when the VME run is more prefer the thread. the allocation of resources to the virtual machine utilizes a fold model: while a fold is popped, completely resources allocated at that fold level come freed. Calls from either an application to a operating patterns come so manufactured by a call for that retains a equivalent run fold, however sustaining a vary inside protection level; the resultant efficiency of supervisor call instruction is one of the features that makes the architecture competitory.

Communication between Virtual Machines is achieved by means of Cases (known as channel) & divided memory areas.

Files & more lasting objects come recorded inside a repository known as the Catalogue. Unlike more operating systems, the filename hierarchy is independent of the locatiin of the file on a particular tape or even disk volume. Inside times in which there was further want for offline storage, this processed it convenient to keep track of files disregardless of their location, & to move files between locations while forgoing renaming the children. Too when files, a Catalogue keeps track of users & user groups, volumes, hardware, network modems, & numerous more resources. Metadatthe for files may be held within an object known as a File Description.

Interrupts come handled by creating a freshly fold frame on a fold for the relevant run, treating the interrupt applying this recently environment, then popping the fold to link to to the interrupted run.

OMF
Loadable object code is maintained around the format known as OMF (Object Module Format). Various compilers come available, besides when utilities, notably a Collector, which links the code around many OMF modules into one module, for further effective loading at begin-period.

SCL
A command language for VME is referred to as SCL (Body Control Language). This is great deal supplementary recognizably the high-level programming language than the job control or even plate languages incurred around virtually all more operating systems: it may be compared to scripting languages like JavaScript, though its surface syntax is from either Algol 68. SCL is designed to allow each line-at-the-period interactional have from either the console, & creation of viable scripts or even software. a declaration of a procedure in SCL when well acts as the definition of a elementary form or even guide permitting the procedure to become invoked from either an interactional terminal. A language is compiled into object module format in the equivalent way when any more VME programing language. SCL is prevent-structured, using begin/end deflects serving a dual & complementary roles of defining a lexical scope of variable declarations, & defining a points at which resources acquired from either a operating patterns should exist as freed. Variables in the language (which come then accessible from either applications in the form of environment variables) may have a total of elementary types like strings, booleans, & whole number, & are besides wont to contain information to technique resources like files & network modems.

Series 39
the Series 39 range introduced Nodal Architecture, a novel implementation of distributed shared memory that can be seen as the hybrid of a multiprocessor system and the cluster design. From each one machine consists of the total of nodes, & from each one node contains its have choose-code processor and independent memory. Virtual machines come usually placed (at any once) in of these node. Discs & more peripheral device come shared between nodes. Nodes come attached applying the high-high-velocity optical bus, which is utilized to provide applications sustaining the virtual divided memory. Memory segments that come marked every bit shared come within point of fact replicated in every node, by owning updates existence broadcast above a inter-node network. Different copies of the divided memory come synchronized whilst the semaphore instruction is executed.

Development process

VME is written completely around S3, the specially-designed system programming language based on Algol 68. Although the high-level language is used, a operating models is non designed to exist as independent of a underlying devices architecture: to the contrary, the softwcome program & devices architecture are closely integrated.

From either its earliest times, VME was developed by owning the help of a software engineering repository known as CADES, built for the purpose using an underlying IDMS database. CADES is non simply the version control system for code modules: it manages all aspects of the computer software lifecycle from either requirements capture across to field maintenance.

Application Development Tools
A application development information offered by having VME fall into 2 categories: third-generation programming languages fourth-generation QuickBuild toolset.

A toolplaced in VME is unco homogeneous, by having virtually all client using the equivalent core set of languages & information. Following, a information come too super easily integrated. Third-person information own manufactured comparatively little impression.

For numbers of years a big majority of VME users wrote applications within COBOL, usually making utilise of the IDMS database and a TPMS transaction processing monitor. More programing language involved FORTRAN, Pascal, and CORAL66, but these served minority interests. Late, in the mid 1980s, a C compiler became available, largely to enable porting of software like relational database systems. the compilers developed inside ICL part a most common architecture, & around a few legal actions part components like code-generators.

SFL
An assembly language SFL is also available, however is non widely utilized (an exception is the VME version of the IDMS database engine).

Quickbuild
A QuickBuild applicatiaround development environment on VME has been extremely successful despite a fact that applications come largely locked in to the VME environment. This environment is centred on the Information Dictionary Technique (DDS), an early & super successful attempt to build the comprehensive repository supporting all the other information, by using to the full trend lines for the development lifecycle. Too when database schemas & file & record descriptions, a lexicon keeps track of objects like reports & enquiry, screen designs, & 4GL code; it likewise supports a kind of system at the requirements capture level, like entity-relationship system and run models.

A QuickBuild 4GL is packaged within both forms: ApplicationMaster for the creation of low TP applications ReportMaster for load coverage.

Two come high-level declarative languages, utilizing Jackson Structured Programming as their design paradigm. ApplicationMaster is unusual withinside its approach to application project therein it focuses on a user session when in case it were going in one colloquial run, entirely hiding the complexness of maintaining state through user interactions. Because a 4GL & more information like a screen designer operate lone by owning a DDS lexicon, which likewise holds a database schemas, there exists considerable reuse of metadata that is seldom achieved sustaining more 4GLs.

Sources

A Architecture of OpenVME. Nic Holt. ICL publication 55480001. Dateless (probably about 1995)