How It All Started…AKA the Birth of the CLR

Hello everyone, I am the Lead Architect of the CLR/UIFX group  and the Chief Architect of the .NET Frameworks.  I was thinking about what I should put in the first entry of my blog… as one of the founders of the CLR I thought it would be interesting to give you some history of how CLR was born in my blog’s intro entry.


Before the CLR I was working on JVM. When Mike Toutonghi, Peter Kukol, Anders Hejlsberg, and I realized that the JVM would not give us the flexibility to innovate in the places we cared about – support for other languages, deep interop with COM and unmanaged code, extensive frameworks to expose MS technology – we decided to join force with the COM team and form a new group,  tentatively named COM 2.0.


We soon disagreed about object management, specifically about explicit management like COM (AddRef/Release) versus automatic management (Garbage Collection), we decided to form 2 groups: COM+ and CLR. This marked the birth of the CLR group.


Early on, we were joined by a meta data group who had been prototyping some meta data schema for the C++ compiler. Peter Kukol and the C++ group collaborated on the IL instruction set. I designed the architecture of the runtime and wrote the Garbage Collector (and yes the GC prototype was was written in Common Lisp first and I wrote a translator to convert it to C++).


Soon we had all the fundamental components of a runtime, some runtime helpers for the base classes (String and Object), and a new cool language: C#. We were in the business to build the full fledge CLR and the Framework.


So there you go, for those curious minds this is how CLR was started.


In the next blog entry I will be writing about server modeling. Also feel free to let me know if there are specific topics you want to see me write about.

Comments (21)

  1. Many people know Patrick Dussud by his outstanding work on Garbage Collection. But did you know he was

  2. shailensukul says:

    The first article was a great recap.

    I would love to see an article on the extensability features of the CLR.



  3. Mike Dimmick says:

    Can you talk about how much of the problem with the JVM was technical and how much political?

  4. Items says:

    Не так давно начал свой блог самый главный разработчик .Net CLR и вообще хороший человек Patrick Dussud

  5. HidekiAI says:

    In your future blogs, I would like to read more about GC.

  6. mjeelani says:

    Great Post Patrick! Looking forward to more insights on the CLR.

  7. tomasr says:

    Great stuff Patrick, and welcome to the community! I wonder at what point did the COR name appear?

  8. demattel says:

    In Common Lisp? Great! Can you write more on this topic?

  9. shakeher says:

    server modelling —- how about a bit of its  history too. seriously,the  above history was great.

  10. error1408 says:

    I’d like to read about WHY you used LISP at first.

    Nice Post. A bit short perhaps 😉

  11. Patrick , one of the founding members of the CLR team, starts a blog by posting a brief bit about this

  12. rbirkby says:

    > and a new cool language: C#

    ho ho ho!

    For an alternate view on the gestation of the CLR check out:

  13. ovidiupl says:

    I’d like to know what order the pieces were built in (specifically: metadata, IL and the JIT compiler, the GC, the security subsystem, AppDomains). It would also be interesting to know what were the goals and the constraints that guided design choices (for instance, why not build a simpler runtime, like a garbage-collected environment for C++, without IL?)

  14. CoqBlog says:

    Vous l’avez sans doute déjà lu, Patrick Dussud , ouvre un blog . Patrick Dussud est un des ingénieurs

  15. Patrick Dussud says:

    About Common Lisp and Lisp in general:

    I have worked on Lisp for many years, and I think it has strength that sets it apart from other dynamic languages. My favorite is the fact that you can extend the Lisp language to create your own special purpose language in a very natural way using macros. Lisp has a very simple syntax (prefix notation). As long as your extensions adhere to that syntax, it is possible to make them seamless. Arguably, CLOS is a very large extension to Common Lisp, even though you don’t need *any* compiler changes to do a pretty good job implementing it on top of regular Common Lisp.

    Last year, I gave a talk at the International Lisp Conference about the need for Lisp to integrate with the CLR (and / or Java). See the following URL

  16. Patrick Dussud says:

    About the GC prototype in Common Lisp.

    A GC system is rather intricate; besides the basic GC components themselves (the memory manager, the object tracing mechanism, the compaction/sweep/copy module, the finalization mechanism) there is a great deal of support coming from the execution engine: root enumeration (from the global roots and the stack), synchronization between the execution engine and the GC, initialization and orderly shutdown. Rather that working on all of the pieces together, I decided to write a simulated environment where I could concentrate on the GC components and once they are working, then I would get it in the execution engine. This way, I wouldn’t be tempted to bend the design of the GC mechanism to satisfy an oddity of the execution engine.

    At the time I wrote it, I could also have used VB, C++, Java. Common Lisp had the best debugging support at the time and I knew how to write a source to source language translator as long as the input source language is Lisp (I wrote an Interlisp to Common Lisp one at Schlumberger and a Zetalisp to Common Lisp one at Texas Instruments).

    I wrote the code in stylized Lisp, keeping in mind that I had to translate the code to C++, so no advanced Lisp features were used (no dynamic feature, no closures).

    Unfortunately, I can’t find the Common Lisp GC sources or the translator anymore; they were left behind on one of my development computers. 🙁

  17. Patrick Dussud says:

    About JVM limitations:

    Well, the JVM has technical limitations that were hard for us to solve: the JVM is designed to execute type safe languages only and we wanted to executed unsafe C++ as well. Solving this would have required the support of the entire Java community and this didn’t make sense for the community at large.

    Other limitation were contractual. We discovered that the compliance test suite didn’t allow us to extend the existing Java classes so it was hard for us to reflect the Windows platform with more fidelity.

    We also discovered that it was very hard to negociate for a different / better Java to Native code interop layer. This was both a technical and political issue: the interop layer is heavily archicture specific – it is hard to make it universal aka Run anywhere-  and it is quite visible to programmers unlike an extension library on the side.

  18. Patrick Dussud says:

    About the rationale for our design decisions:

    First and foremost, we wanted to support safe execution of type safe languages . We designed a security model to separate trusted code from untrusted code and app domains to isolate code execution contexts from each other. We also wanted to be able to recompile an existing C++ application with an extra /CLR flag and run this application under the CLR. These high level goals lead us to where we are now. We briefly thought about a small GCed runtime for C++ but because C++ isn’t type safe, it wasn’t that interesting to us. Also you are severely limited in the ability to manage memory automatically for a language which can "hide" references in other datatypes or even by adding extra bits to the reference and such clever tricks.  

  19. I thought Thanksgiving morning is for adults to be sleeping in. Instead, not only are the kids up at the crack at dawn but one (the eight year old) is playing games on Vista and asking for Starbucks, while the nearly 4 year old is clamoring for princess

  20. sinetif says:

    "Other limitation were contractual. We discovered that the compliance test suite didn’t allow us to extend the existing Java classes so it was hard for us to reflect the Windows platform with more fidelity."

  21. SHREK says:


    Start was GREAT! Tell us about CLR history more, please…