The Origin of the “MIT License”
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Department: Anecdotes Editor: David Walden, dave@walden-family.com The Origin of the “MIT License” Jerome H. Saltzer Massachusetts Institute of Technology & THE “MIT LICENSE” has become a popular demonstrate that TCP/IP implementations could way of releasing copyrighted computer pro- be small, fast, and usable in an engineering work- grams for others to use without requiring signa- station or a personal computer. Descended from tures or a license fee. The quoted words refer to that starting point were a translation of the BCPL a group of software licenses that have common code into the C language by Larry Allen4 for use ancestry and guiding principles but varying on the Digital Equipment PDP-11 and, led by wordings. There has been some recent discus- Wayne Gramlich,5 a TCP/IP implementation with sion about the origin of the “MIT License,”1 but network applications for the IBM Personal Com- that discussion has been inconclusive because puter (PC/IP)6 by John Romkey,7 David Bridg- authoritative historical documentation has been ham,8 Karl Wright,9 Don Gillies,10 and Louis missing or hard to find. This note provides some Konopelski.11 Separately, Noel Chiappa12 devel- of that history and documentation. Being com- oped a multiprotocol network routing system, posed 35 years after the events involved, it relies known as the C-Gateway, for the Digital Equip- primarily on my often-flaky recollections but it ment LSI-11, for which Liza Martin13 implemented also offers some relevant supporting documenta- the External Gateway Protocol (EGP).14 tion found in my files and in online archives. Because the requests were coming from both In the fall of 1983, the Computer Systems university researchers and commercial organiza- Research (CSR) Group of the MIT Laboratory for tions, there was an ongoing discussion within the 2 Computer Science (MIT–LCS) had developed group about what conditions should accompany several pieces of network software that were gen- distribution of these materials. The option of erating outside interest and requests for both attaching a copyright notice to software and its information and copies of the code. One of these documentation had recently been clarified by 3 pieces was David Clark’s BCPL implementation Congress and the U.S. Copyright Office. But that of a TCP/IP stack for the Xerox Alto, intended to option raised a further question: if copyrighted, should MIT require a written contract and impose a license fee? The group’s primary goal Digital Object Identifier 10.1109/MAHC.2020.3020234 was to influence the way networking was done, Date of current version 15 November 2020. and it seemed likely that licensing revenue would 94 1058-6180 ß 2020 IEEE Published by the IEEE Computer Society IEEE Annals of the History of Computing Figure 2. Enclosure accompanying the letter of Figure 1, illustrating an example copyright and Figure 1. Memorandum of January 10, 1984 permission notice used by the ACM. (misdated 1983) to attorneys, proposing suggested wording for a copyright and permission notice. The cited enclosure is shown in Figure 2. memorandum, a page from a then-recent issue of the Communications of the ACM that exhibits their not amount to much. Anecdotal experience of copyright and permission notice wording. The other software groups at MIT–LCS also suggested attorneys soon responded favorably, and on Janu- that much time would be spent with attorneys ary 25, 1984, we sent an announcement describing preparing and then negotiating licensing agree- the change in permission policy to about 25 recipi- ments. Based on these considerations, we con- ents of the June 1, 1983 “please do not distribute cluded that it would be better to give the any further” version of PC/IP. software away with a copyright notice that identi- There were four guiding principles underly- fied where it came from and did not require any ing this copyright and permission notice: signatures. Larry Allen and I began conversations with 1. Permission is granted for any purpose, attorneys Bob Sullivan15 and Sib Reppert16 of the including commercial use. Boston law firm that at the time was handling intel- 2. Neither signed agreement nor license fee is lectual property matters for MIT–LCS. In January required. 1984, Larry and I drafted proposed wording based 3. Permission is subject to three restrictions: on the idea of copyrighting the software but Any redistribution must credit MIT. including with the copyright notice a permission Any redistribution must include the same notice that allowed anyone to use it for free. The copyright and permission notice. wording borrowed ideas and phrases that had Promotional use of MIT’s name is restricted. been used in the research group’s previous 4. The software is provided “as-is” without restricted distribution notices and it also bor- warranty. rowed from the copyright and permission notice that the Association for Computing Machinery Discussion over the next few days refined the had recently begun attaching to articles in its wording, omitting the word “sale” since it was publications. Figure 117 is a memorandum to redundant with the words “any purpose” and the attorneys presenting the draft wording and slightly relaxing the restriction on promotional Figure 218 is an excerpt from an attachment to that use of MIT’s name. The refined wording was first October-December 2020 95 Anecdotes Figure 3. Copyright notice for C language programs first used in the February 1, 1984 distribution of PC/IP and the distributions later that year of the C-Gateway and EGP for the LSI-11. used for the February 1, 1984 distribution of PC/ concern, they also added a sentence that the IP. Figure 319 is a copy of the include.h file used software did not include anything licensed as for C-language programs that made up PC/IP and part of the Unix system. The reworded license of the EGP implementation for the C-Gateway. This Figure 424 was first applied to the X Window Sys- version of the notice is probably the first one tem Version 10 Release 3 in February, 1986. This that would be appropriate to identify as the wording could be thought of as the second ver- “MIT License.” Previous software distributions sion of the “MIT License.” by the research group had used copyright noti- Many more versions of this license have ces with one or more elements based on the since been adapted with minor wording changes same guiding principles, but this seems to be by organizations at MIT and elsewhere, including the first one that combined all four principles in all of the software developed by Project Athena. a single license. The term “MIT License” has been used both spe- In the fall of 1985, the question arose of how cifically to refer to the X10R3 license and generi- to license the X Window System20 that was being cally to identify almost any permissive free developed by Jim Gettys21 and Bob Scheifler22 software license that has this ancestry and is for MIT Project Athena.23 In discussions parallel based on the same four principles.25 to those of two years earlier, they had noticed As it turned out, the licensing strategy had that proprietary licensing of early versions of the desired effect: the goal of influence was real- the X Window System was becoming a hassle ized. PC/IP became the basis for a dozen or so both for them and for prospective recipients commercial networking stacks for the IBM Per- and had the potential of interfering with wide- sonal Computer. The X Window System became spread adoption. There were significant contri- the standard window system for Unix and Linux butions made by early adopters, but that only and is running on millions of systems today. made it more apparent that it was important to Project Athena’s Kerberos authentication sys- minimize the licensing friction. They also noted tem26 is included in many computer system that there were similar competing window sys- distributions, notably including Microsoft Win- tem projects going on at both Sun Microsystems dows, Apple macOS, most versions of Unix and and Carnegie Mellon University and both were Linux, and IBM z/OS. requiring a signed license. The conclusion was Furthermore, the good will that was gained that the X Window System might be more influ- from free distribution of these software pack- ential if adopting it could be simpler. ages led to the flow back of both funding and A new group of attorneys went over the word- software applications that support research and ing of the PC/IP copyright and permission noti- education at MIT. The cash flow has dwarfed the ces and added several words of the kind beloved forgone revenue stream that likely would have by attorneys while maintaining the four guiding come from licensing for a fee, and even that sum principles. For the specific purpose of assuring X has been dwarfed by the value of the applica- Window System recipients about a potential tions that became available. A lesson is that it 96 IEEE Annals of the History of Computing Figure 4. Copyright notice for C language programs first used in the X10R3 release of 22 February 1986 of the X Window System. can be important to look past the prospect of 4. Larry W. Allen, MIT–LCS staff member in 1983. licensing for a fee, which may bring in a few dol- 5. Wayne C. Gramlich, MIT EECS graduate student in lars, and instead see the opportunity that opens 1983. if you give the software away. The potential 6. J. H. Saltzer, D. D. Clark, J. L. Romkey, and reward can be orders of magnitude larger.