emas.bobeager.uk The Edinburgh Multi Access System Link to http://youtube.bobeager.uk


This page provides information about the Edinburgh Multi-Access System, which I worked on for about 8 years. Its primary purpose is to provide supporting information for my lecture The Edinburgh Multi Access System, first given to the Computer Conservation Society.

The Lecture

The following direct material is available:


The lecture would not have been possible without the help (over the last 40 or so years) of a large number of people.

I would like to thank anyone who was part of the EMAS team; thank you for your spendid work. I may not have met all of you, but your names are familiar to me from reading documentation (and source code!)

I am particularly grateful to those at Edinburgh with whom I had the pleasure of working (and eating and drinking). These are just a few of the people I worked with a lot, or to whom I owe a great deal; implicit thanks to anyone whom I have left out. Those marked with an asterisk (*) are sadly no longer with us; there may be more in that category of whom I am not aware. They include:

Colin Adams, Gordon Brebner, Mike Brown, Gordon Burns*, Scott Currie, Tony Gibbons*, Brian Gilmore, Bill Hay, Stephen Hayes, John Henshall*, George Howat, Bill Laing, Colin McArthur, Colin McCallum*, Roderick McLeod, Geoff Millard*, Brian Murdoch, John Murison, David Rees, Sandy Shaw*, Felicity Stephens, Peter Stephens*, Peter Robertson, Nick Shelness, John Wexler*, Harry Whitfield, Alex Wight, Keith Yarwood*


There are many references, including all of the documents in the repository mentioned below in the Links section. The most important ones are linked here. Some are published papers, and others are gleaned from rescued internal reports.

EMAS (or EMAS-1)

The Edinburgh Multi Access System
This is the original paper on EMAS.
The EMAS Director
This explains the Director, and its function in implementing the filing system.
The Standard EMAS Subsystem
This concerns the usual user interface to EMAS, although other subsystems can be used.
The EMAS Archiving Program
This important component provided offline storage for files, helping to keep the main filing system clear of rarely used files.
Edinburgh Multi Access System User Manual
The preliminary user manual issued when EMAS first offered a full service.
EMAS User's Guide
The User's Guide for the system. There is a small update here.

EMAS 2900 (or EMAS-2)

The EMAS 2900 Operating System
This is the principal paper on the second implementation of EMAS, on the ICL 2900.
An Experiment In Doing It Again, But Very Well This Time
The famously named paper on the process of re-implementing EMAS on the ICL 2900.
The Kernel of the EMAS 2900 Operating System
This paper describes the paging system, and (inter alia) the interaction between components such as the Director, Local Controller and Global Controller.
EMAS 2900 User's Guide
The User's Guide for EMAS 2900; some commands are changed or enhanced.
Introduction to EMAS
A simple introductory guide to the system.
The ICL 2900 Series
Probably the only actual book published about the ICL 2900. Rather superficial in places, no doubt because of legal issues; however, it is still interesting and informative.


EMAS-3 User's Guide
The User's Guide for EMAS-3; many commands are changed or enhanced.
Mail on EMAS-3
The manual for using electronic mail of EMAS-3. Much of this also applies to EMAS 2900.


EMAS 2900: Concepts
A particularly useful document, describing the history of EMAS until about 1981. There is also a good overview of its inner workings.
The IMP language and compiler
EMAS was implemented almost entirely in the IMP programming language, based on Atlas Autocode. This describes the language, and the workings of its compiler.
Edinburgh IMP Language Manual
Describes the version of IMP used on EMAS, which was also available on EMAS 2900.
The IMP80 Language
Describes the slightly revised version of IMP used later on EMAS 2900, and on EMAS-3.
Atlas Autocode Reference Manual
An early manual on Atlas Autocode, which is a direct ancestor of the IMP language.
Atlas Autocode Mini Manual
An abbreviated manual for Atlas Autocode, which is a direct ancestor of the IMP language.


Some EMAS and ICL 2900 related anecdotes are here:

  • There is a wealth of material in my file repository. Nearly all of the material there is from documents I managed to preserve or rescue, with some from members of the EMAS team. It can be found at http://www.ancientgeek.org.uk/EMAS/.
  • epocalc is an interesting computer history site

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Last updated: 20 Sep 2023