EMAS

EMAS was originally built for an ICL System 4-75 computer but later implemented for an ICL 2900 computer and then an IBM System/370. It had provision for fully interactive and background processing. EMAS was written almost entirely in the Edinburgh IMP programming language, a development of Atlas Autocode. EMAS had several features that were advanced for the time, including dynamic linking, a three-level virtual storage system, an efficient scheduler, a separate user-space kernel ('director'), a user-level shell ('basic command interpreter'), a comprehensive archiving system and a memory-mapped file architecture. Even though slowly superseded by Unix in the late 1980s, as long as it was available, EMAS remained the preferred operating system for a significant number of Edinburgh users. The last machine running EMAS was switched off in 1992.

More information about EMAS can be found on Wikipedia at: 

H. Whitfield and A.S. Wight, The Computer Journal, Volume 16, Issue 4, 1973, Pages 331–346

Abstract: EMAS is a general-purpose time-sharing system for the ICL System 4-75 computer, with provision for fully interactive and background processing. It is a virtual memory system with a three level storage hierarchy. An outline description of the system is given together with a more detailed description of the paging and scheduling software, which is based on the working set concept. Detailed performance figures are included.

P.D. Stephens, The Computer Journal, Volume 17, Issue 3, 1974, Pages 216–223

Abstract: The EMAS general purpose time sharing system is notable for being coded entirely in IMP, a high level language, which was developed from Manchester University's Atlas Autocode specifically for system programming. This paper describes the main features of the language and the implementation used for EMAS.

D.J. Rees, The Computer Journal, Volume 18, Issue 2, 1975, Pages 122–130

Abstract: The EMAS (Edinburgh Multi-Access System) Director is the paged part of the EMAS operating system program. A description of its position in the EMAS system, its functions and its implementation is given with particular reference to its main components, the file system and the console input/output system.

A.S. Wight, The Computer Journal, Volume 18, Issue 2, 1975, Pages 131–134

Abstract: The Edinburgh Multi-Access System (EMAS) has been described (Whitfield and Wight, 1973). The service now (March 1974) supports up to 55 simultaneous users from an accredited population of 500. File storage is provided on a 700M byte disc-file. Magnetic tape is used to provide backup and archive facilities for the file system. These facilities have been improved as use of the system expanded. Details of the use of tape as another level in the storage hierarchy are given and also included are outline plans to cope with two linked systems each with 700M bytes of disc-file and an ICL 4-75 processor.

G.E. Millard, D.J. Rees and H. Whitfield The Computer Journal, Volume 18, Issue 3, 1975, Pages 213–219

Abstract: The user image of the Edinburgh Multi-Access System (EMAS) is provided by a subsystem. The structure of the standard subsystem and its relationship to the supervisor and director is described. A description is given of conventions introduced by the subsystem for the organisation of files and the standard facilities with which a user is provided.