Edinburgh Multiple Access System
Encyclopedia
The Edinburgh Multi-Access System (EMAS) was a mainframe computer
operating system
developed at the University of Edinburgh
, Scotland
, during the 1970s. EMAS was developed because none of the manufacturers' operating systems (nor independent systems such as Multics
) came close to satisfying the demanding performance requirements of Edinburgh University.
Originally running on the ICL System 4/75 mainframe (based on the design of the IBM 360) it was later reimplemented on the ICL 2900 series of mainframes (as EMAS 2900 or EMAS-2) where it ran in service until the mid 1980s. Near the end of its life, the refactored version was back-ported (as EMAS-3) to the IBM System/370-XA architecture again, running on Amdahl
470 and NAS VL80 IBM mainframe clones into the early 1990s. It was a powerful and efficient general purpose multi-user
system which supplied all the computing needs of Edinburgh University and the University of Kent
(the only other site outside Edinburgh to adopt the operating system). The final EMAS system (the Edinburgh VL80) was decommissioned in July 1992.
EMAS had several advanced (for the time) features, including dynamic linking, multi-level storage, an efficient scheduler
, a separate user-space kernel
('director'), a user-level shell
('basic command interpreter'), and a memory-mapped file
architecture. Such features lead EMAS supporters to claim that their system was superior to Unix
for the first 20 years of the latter's existence.
The Edinburgh Computer History Project is attempting to salvage some of the lessons learned from the EMAS project and has the complete source code of EMAS online for public browsing.
EMAS was written entirely in the Edinburgh IMP
programming language
, with only a small number of critical functions using embedded assembler within IMP sources.
Mainframe computer
Mainframes are powerful computers used primarily by corporate and governmental organizations for critical applications, bulk data processing such as census, industry and consumer statistics, enterprise resource planning, and financial transaction processing.The term originally referred to the...
operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
developed at the University of Edinburgh
University of Edinburgh
The University of Edinburgh, founded in 1583, is a public research university located in Edinburgh, the capital of Scotland, and a UNESCO World Heritage Site. The university is deeply embedded in the fabric of the city, with many of the buildings in the historic Old Town belonging to the university...
, Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
, during the 1970s. EMAS was developed because none of the manufacturers' operating systems (nor independent systems such as Multics
Multics
Multics was an influential early time-sharing operating system. The project was started in 1964 in Cambridge, Massachusetts...
) came close to satisfying the demanding performance requirements of Edinburgh University.
Originally running on the ICL System 4/75 mainframe (based on the design of the IBM 360) it was later reimplemented on the ICL 2900 series of mainframes (as EMAS 2900 or EMAS-2) where it ran in service until the mid 1980s. Near the end of its life, the refactored version was back-ported (as EMAS-3) to the IBM System/370-XA architecture again, running on Amdahl
Amdahl Corporation
Amdahl Corporation is an information technology company which specializes in IBM mainframe-compatible computer products. Founded in 1970 by Dr. Gene Amdahl, a former IBM employee, it has been a wholly owned subsidiary of Fujitsu since 1997...
470 and NAS VL80 IBM mainframe clones into the early 1990s. It was a powerful and efficient general purpose multi-user
Multi-user
Multi-user is a term that defines an operating system or application software that allows concurrent access by multiple users of a computer. Time-sharing systems are multi-user systems. Most batch processing systems for mainframe computers may also be considered "multi-user", to avoid leaving the...
system which supplied all the computing needs of Edinburgh University and the University of Kent
University of Kent
The University of Kent, previously the University of Kent at Canterbury, is a public research university based in Kent, United Kingdom...
(the only other site outside Edinburgh to adopt the operating system). The final EMAS system (the Edinburgh VL80) was decommissioned in July 1992.
EMAS had several advanced (for the time) features, including dynamic linking, multi-level storage, an efficient scheduler
Scheduling (computing)
In computer science, a scheduling is the method by which threads, processes or data flows are given access to system resources . This is usually done to load balance a system effectively or achieve a target quality of service...
, a separate user-space kernel
Kernel (computing)
In computing, the kernel is the main component of most computer operating systems; it is a bridge between applications and the actual data processing done at the hardware level. The kernel's responsibilities include managing the system's resources...
('director'), a user-level shell
Shell (computing)
A shell is a piece of software that provides an interface for users of an operating system which provides access to the services of a kernel. However, the term is also applied very loosely to applications and may include any software that is "built around" a particular component, such as web...
('basic command interpreter'), and a memory-mapped file
Memory-mapped file
A memory-mapped file is a segment of virtual memory which has been assigned a direct byte-for-byte correlation with some portion of a file or file-like resource. This resource is typically a file that is physically present on-disk, but can also be a device, shared memory object, or other resource...
architecture. Such features lead EMAS supporters to claim that their system was superior to Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
for the first 20 years of the latter's existence.
The Edinburgh Computer History Project is attempting to salvage some of the lessons learned from the EMAS project and has the complete source code of EMAS online for public browsing.
EMAS was written entirely in the Edinburgh IMP
Edinburgh IMP
Edinburgh IMP is a development of ATLAS Autocode, initially developed around 1966-1969 at Edinburgh University, Scotland. IMP was a general-purpose programming language which was used heavily for systems programming....
programming language
Programming language
A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....
, with only a small number of critical functions using embedded assembler within IMP sources.