# Simula

Simula is the name of two simulation programming languages, Simula I and Simula 67, developed in the 1960s at the Norwegian Computing Center in Oslo, by Ole-Johan Dahl and Kristen Nygaard. Syntactically, it is an approximate superset of ALGOL 60,$^{:1.3.1}$ and was also influenced by the design of SIMSCRIPT.
Simula 67 introduced objects,$^{:2,5.3}$ classes,$^{:1.3.3,2}$ inheritance and subclasses,$^{:2.2.1}$ virtual procedures,$^{:2.2.3}$ coroutines,$^{:9.2}$ and discrete event simulation,$^{:14.2}$ and featured garbage collection.$^{:9.1}$ Other forms of subtyping (besides inheriting subclasses) were introduced in Simula derivatives.
Simula is considered the first object-oriented programming language. As its name suggests, the first Simula version by 1962 was designed for doing simulations; Simula 67 though was designed to be a general-purpose programming language and provided the framework for many of the features of object-oriented languages today.
Simula has been used in a wide range of applications such as simulating very-large-scale integration (VLSI) designs, process modeling, communication protocols, algorithms, and other applications such as typesetting, computer graphics, and education.
Computer scientists such as Bjarne Stroustrup, creator of C++, and James Gosling, creator of Java, have acknowledged Simula as a major influence. Simula-type objects are reimplemented in C++, Object Pascal, Java, C#, and many other languages.

## History

The following account is based on Jan Rune Holmevik's historical essay.
Kristen Nygaard started writing computer simulation programs in 1957. Nygaard saw a need for a better way to describe the heterogeneity and the operation of a system. To go further with his ideas on a formal computer language for describing a system, Nygaard realized that he needed someone with more computer programming skills than he had. Ole-Johan Dahl joined him on his work in January 1962. The decision of linking the language up to ALGOL 60 was made shortly after. By May 1962, the main concepts for a simulation language were set. SIMULA I was born, a special purpose programming language for simulating discrete event systems.
Kristen Nygaard was invited to visit the Eckert–Mauchly Computer Corporation in late May 1962 in connection with the marketing of their new UNIVAC 1107 computer. At that visit, Nygaard presented the ideas of Simula to Robert Bemer, the director of systems programming at Univac. Bemer was a great ALGOL fan and found the Simula project compelling. Bemer was also chairperson of a session at the second international conference on information processing hosted by International Federation for Information Processing (IFIP). He invited Nygaard, who presented the paper "SIMULA – An Extension of ALGOL to the Description of Discrete-Event Networks".
The Norwegian Computing Center got a UNIVAC 1107 in August 1963 at a considerable discount, on which Dahl implemented the SIMULA I under contract with UNIVAC. The implementation was based on the UNIVAC ALGOL 60 compiler. SIMULA I was fully operational on the UNIVAC 1107 by January 1965. In the following few years, Dahl and Nygaard spent a lot of time teaching Simula. Simula spread to several countries around the world and SIMULA I was later implemented on other computers including the Burroughs B5500 and the Russian Ural-16.
In 1966 C. A. R. Hoare introduced the concept of record class construct, which Dahl and Nygaard extended with the concept of prefixing and other features to meet their requirements for a generalized process concept. Dahl and Nygaard presented their paper on Class and Subclass declarations at the IFIP Working Conference on simulation languages in Oslo, May 1967. This paper became the first formal definition of Simula 67. In June 1967, a conference was held to standardize the language and initiate a number of implementations. Dahl proposed to unify the type and the class concept. This led to serious discussions, and the proposal was rejected by the board. Simula 67 was formally standardized on the first meeting of the Simula Standards Group (SSG) in February 1968.
Simula was influential in the development of Smalltalk and later object-oriented programming languages. It also helped inspire the actor model of concurrent computation although Simula only supports coroutines and not true concurrency.
In the late sixties and the early seventies, there were four main implementations of Simula:
* UNIVAC 1100 by Norwegian Computing Center (NCC)
* System/360 and System/370 by NCC
* CDC 3000 by University of Oslo's Joint Computer Installation at Kjeller
* TOPS-10 by Swedish National Defence Research Institute (FOA)
These implementations were ported to a wide range of platforms. The TOPS-10 implemented the concept of public, protected, and private member variables and procedures, that later was integrated into Simula Standard in 1986.
Simula Standard 1986 is the latest standard and is ported to a wide range of platforms. There are mainly four implementations:
* Simula AS
* Lund Simula
* GNU Cim
* Portable Simula Revisited
In November 2001, Dahl and Nygaard were awarded the IEEE John von Neumann Medal by the Institute of Electrical and Electronics Engineers "For the introduction of the concepts underlying object-oriented programming through the design and implementation of SIMULA 67". In April 2002, they received the 2001 A. M. Turing Award by the Association for Computing Machinery (ACM), with the citation: "For ideas fundamental to the emergence of object oriented programming, through their design of the programming languages Simula I and Simula 67." Dahl and Nygaard died in June and August of that year, respectively, before the ACM Turing Award Lecture that was scheduled to be delivered at the November 2002 OOPSLA conference in Seattle.
Simula Research Laboratory is a research institute named after the Simula language, and Nygaard held a part-time position there from the opening in 2001. The new Computer Science building at the University of Oslo is named Ole Johan Dahl's House, in Dahl's honour, and the main auditorium is named Simula.