1. Early History of Object Oriented Programming
Per Kjeldaas

2. Who Was First? Not C++ Not Smalltalk
Simula 67 is recognized as the first object-oriented language (1967)

3. What Was the Need? Simulation needed interactive processes
Algol, Fortran and Cobol were inadequate for modeling complexity
Monte Carlo simulation was done by hand

4. Marriage of Two Disciplines
Kristen Nygaard was expert operations analyst
Ole-Johan Dahl was an expert computer scientist and programmer

5. Simula I

6. Quasi-Parallel Processing
Basis for today’s Java threads
Co-routines
Ability to yield control from inside a process when simulated time advances
Other processes will take control in the meantime
Earlier than time sharing (Multics)

7. Simula 67 - Objects and Classes
Station and customer concepts merged into the object concept
Classes of objects are described in the class declaration, just like what Java has adopted
Most current OO programming features come from Simula

8. Reference Variables and “new”
ref (Invoice) inv;
inv :- new Invoice(1511);
Again, Java has adopted it in a similar way

9. Subclasses and Inheritance
order class batch order;
begin integer batch size; end;
order class single order;
begin real finishing time, weight; end;
single order class plate;
begin real length, width; end;

10. Polymorphism Virtual functions - like methods in Java
The “inner” mechanism
class Person;
begin
<statements 1>
inner;
<statements 2>
end;

11. Heap and Garbage Collector
Algol’s stack was inadequate
Object storage required heap
Garbage collector was also needed
Both features were in Simula 67

12. “Remote” Object Connection
inspect (element expression) when A1 do S1
when A2 do S2
when An do Sn
otherwise S;
Adopted by Java as:
if (x instanceOf A) { …}

13. Components and Packages
Implemented as classes within a class
In Simula 67, simulation-specific functionality implemented in the Simulation package (class)

14. Real-Time Simula Was planned in 1970
To be used for modeling an operating system
Was never implemented, however

15. Why did it not spread? Expensive Misguided government policies
Donald Knuth of Stanford U wanted it, but did not want to pay -- did not get it!
Few publications in English
The Simula name

16. Finally Catching On
Alan Kay used “bootleg” copy of Simula 67 for CDC as basis for Smalltalk
Bjarne Stroustrup gave Simula credit as the main basis for C++

17. Finally Catching On
James Gosling of Sun referenced Simula as Java’s basis at JavaOne
Many universities used Simula as the OO teaching language during the 80’s and 90’s

18. Postscript
OO would have reached the world much earlier if a number of administrative errors had not been made
Dahl and Nygaard only got their recognition, the ACM Turing award, also known as the Nobel prize of computing, in 2002
They both died a few months later

19. References
ACM - Association for Computing Machinery, Press release: A.M. Turing Award, February 6, Retrieved last on October 23, 2004 from
Dahl, O.-J.: The Birth of Object Orientation: the Simula Languages, Retrieved last on October 23, 2004 from the University of Oslo’s web site at
Dahl, O.-J., B. Myhrhaug & K. Nygaard: Some Features of the Simula 67 Language, Dec. 1968, Proceedings of the second conference on Applications of simulations, Winter Simulation Conference (ACM, IEEE), New York, NY
Dahl, O.-J., K. Nygaard: SIMULA: an ALGOL-based simulation language, Communications of the ACM, v.9 n.9, p , September, 1966
Gosling, J., A. Baratz: Opening Keynote Session at JavaOne. May 29, 1996, San Francisco, CA. Retrieved last on October 23, 2004 from.
Holmevik, J. R.: Compiling SIMULA: A Historical Study of Technological Genesis. IEEE Annals of the History of Computing, Vol. 16, No. 4, 1994, Pages: (Also retrieved last on October 23, 2004 from
Krogdahl, S.: The birth of Simula, HiNC 1 Conference in Trondheim, Norway, June 2003 (IFIP WG 9.7, in cooperation with IFIP TC 3) (Also retrieved last on October 25, 2004 from
Nygaard, K., O.-J. Dahl: The development of the SIMULA languages. The first ACM SIGPLAN conference on History of programming languages, 1978, Los Angeles, CA. Pages:
Sklenar, J.: Introduction to OOP in SIMULA, 1997, retrieved last on October 23, 2004 from
Stroustrup, B.: A History of C++: ACM SIGPLAN Notices, March The second ACM SIGPLAN conference on History of programming languages, 1993, Cambridge, MA. Pages:
Vaucher, Jean G.: DIRO Simula home, Retrieved last on October 23, 2004 from