Later, release 3. 0 leveraged the enhancements of newer Intel 486 and Intel Pentium processors — the Virtual Interrupt Flag ( VIF ), which was part of the Virtual Mode Extensions ( VME )— to solve this problem.

In practice, a VME Virtual Machine is closer to the concept of a process on other operating systems, while a VME process is more like a thread.

It ran the VME operating systems, and supported emulation of both the earlier architectures ( 1900 Series and System 4 ), either standalone ( DME, Direct Machine Environment ) or concurrently with native-mode operation ( CME, Concurrent Machine Environment ).

This, and the fact that some users were not moving to the new system, led ICL to develop a system called Concurrent Machine Environment ( CME ) under which VME ran DME as a subsystem, enabling 1900 and System 4 applications to be run on a 2900 or Series 39 machine alongside VME applications.

Originally developed in the 1970s ( as VME / B, later VME 2900 ) to drive ICL's then new 2900 Series mainframes, the operating system is now known as OpenVME incorporating a Unix subsystem, and runs on ICL Series 39 and Trimetra mainframe computers, as well as industry-standard x64 servers.

As a creation of the mid-1970s, with no constraints to be compatible with earlier operating systems, VME is in many ways more modern in its architecture than today's Unix derivatives ( Unix was designed in the 1960s ) or Microsoft Windows ( which started as an operating system for single-user computers, and still betrays those origins ).

VME is structured as a set of layers, each layer having access to resources at different levels of abstraction.

The toolset on VME is unusually homogeneous, with most customers using the same core set of languages and tools.

The primary language used for developing both the VME operating system itself and other system software such as compilers and transaction processing monitors is S3.

The VME eXtensions for Instrumentation ( VXI ) bus architecture is an open standard platform for automated test based on the VMEbus.

This is the system used in most computer buses predating PCI, such as the VME bus.

The Navy is replacing the KG-38 used in nuclear submarines with KOV-17 circuit modules incorporated in new long-wave receivers, based on commercial VME packaging.

The Indigo R3000 is effectively a reduced cost 4D / 35 without a VME bus.

The PXI market is also larger than the VME eXtensions for Instrumentation ( VXI ) market at an estimated size in 2007 of.

VME was viewed as primarily competing with the System / 360 IBM mainframe as a commercial operating system, and adopted the EBCDIC character encoding.

" Not only was too much resource going into VME / K at the expense of the VME / B system that ICL's biggest customers were actually using, but the development of mainframe systems was also diverting expenditure from small business systems such as the 2903, whose sales were growing much more rapidly.

This happened just at the time that VME / K had finally reached a level of performance and reliability that made it saleable ; however, the customer base was very small, and by this time VME / B ( which was renamed VME 2900 ) had also matured sufficiently to give confidence that it would meet the future requirements for the entire mainframe range.

* ICL's VME operating system

ICL also produced versions for its ICL 2903 system and for the VME / K operating system.

The term " New Range " was used during development for the product line that was eventually launched as the 2900 Series, the operating system being known initially as VME / B and later simply as VME.

These ran the VME and DME ( emulation ) operating systems, and were available in both single and multi-processor configurations, the later being known as Duals and SuperDuals ( 2966 and 2988 only ).

ICL also produced a version on its VME / K operating system

* S3 ( programming language ), a language used to write the VME operating system and much other system software on the ICL 2900 Series

* Data dictionary system of ICL's VME operating system ; see ICL VME # Quickbuild

* SFL ( programming language ), or System Function Language, of the ICL VME operating system

* ICL VME # SCL ( System Control Language ), of the ICL VME operating system

That the Motorola 680x0 family and VME board computer system vendors were nearing their end of life might have affected the unpopularity of OS-9000 / 680x0.

VME was originally written almost entirely in S3, a specially-designed system programming language based on Algol 68 ( however, VME / K was written primarily in the SFL assembly language ).

This was used for the development of VME / K, whose designers were not confident that a high-level language could give adequate performance, and also for the IDMS database system on account of its origins as a third-party product.

The company also developed a * Content Addressable File Store ( CAFS ) that could be exploited by the VME file system and ICL 2900 IDMS and * the world's first commercially available massively parallel computer, the Distributed Array Processor ( DAP ), that first ran as an attached processor to the ICL 2980.

* VME / B ( originally System B ), targeted at large processors such as the 2970 / 2980 and developed in Kidsgrove, Staffordshire and West Gorton, Manchester

* VME / K ( originally System T ), targeted at the mid-range systems such as the 2960 and developed at Bracknell after the original design for these small processors, System D, was dropped.

VME / K was developed and introduced to the market but was eventually replaced by VME / B

VME / K was developed independently ( according to Campbell-Kelly, " on a whim of Ed Mack "), and was delivered later with the smaller mainframes such as the 2960.

From its earliest days, VME was developed with the aid of a software engineering repository known as CADES, built for the purpose using an underlying IDMS database.

Related families of assemblers for other architectures ( CALM-xx running under VME, PALM-xx developed in Pascal and running on various hosts ) were developed for internal use.

System D was dropped in order to focus efforts on VME / B and System T, renamed to VME / K ( Confusingly, VME / B was developed in Kidsgrove, VME / K in Bracknell.

DME was developed so that customers could buy the new hardware and run their 1900 or System 4 applications whilst they developed their replacement VME applications.

This was later renamed " VME ", short for Versa Module European, by Lyman ( Lym ) Hevle, then a VP with the Motorola Microsystems Operation.

Perhaps more significantly, VME / K was the brainchild of Ed Mack, who had been brought in by managing director Geoff Cross as ICL's head of research and development.

The VXIbus grew from the VME bus specification, it was established in 1987 by Hewlett Packard ( now Agilent Technologies ), Racal Instruments ( now EADS North America Test and Services ), Colorado Data Systems, Wavetek and Tektronix.