CompSci Today’s topics OS & Society Software development models Reading Open Source definitions Microsoft Corp., "Some Questions Every Business Should Ask About the GNU General Public License (GPL)", 2001 Brookshear, Chapter 6

CompSci OS & Software Development 1. Who writes software? 2. How are they paid for it? l How is software developed?

CompSci UNIX: History of an OS l 1969: UNIX created ä Private research project at Bell Labs ä High-level language used by system and application developers ä Good programming interface  Sophisticated apps l 1971: First edition released l 1972: Dennis Ritchie rewrites B ä What did he call the new language? l 1977: Berkeley Software Design releases BSD Unix l UNIX is ubiquitous in research institutions

CompSci Richard Stallman’s quest l In January 1984 I quit my job at MIT and began writing GNU software. Leaving MIT was necessary so that MIT would not be able to interfere with distributing GNU as free software. If I had remained on the staff, MIT could have claimed to own the work, and could have imposed their own distribution terms, …. I had no intention of doing a large amount of work only to see it become useless for its intended purpose: creating a new software- sharing community.

CompSci From software to politics? l Help change the world?

CompSci A post from 1991 Hello everybody out there using minix - I'm doing a (free) operating system (just a hobby, won't be big and professional like gnu) for 386 (486) AT clones. This has been brewing since april, and is starting to get ready. I'd like any feedback on things people like/dislike in minix, as my OS resembles it somewhat (same physical layout of the file-system (due to practical reasons) among other things). I've currently ported bash (1.08) and gcc (1.40),and things seem to work.This implies that I'll get something practical within a few months, and I'd like to know what features most people would want. Any suggestions are welcome, but I won't promise I'll implement them :-) Linus PS. Yes - it's free of any minix code, and it has a multi-threaded fs. It is NOT protable (uses 386 task switching etc), and it probably never will support anything other than AT-harddisks, as that's all I have :-(

CompSci Linux Timeline l 10/1991 : v first usable Linux l 01/1992 : v first 'actually working' version, under GPL l 03/1992 : comp.os.linux l 04/1992 : v capable of using X l 09/1992 : Linux stops being Minix-like and becomes UNIX- like l 03/1994 : 1.0 l 06/1996 : l 12/2003 : l What is Linux? ä Freely available OS ä Based on Linux kerrnel developed by Torvalds ä Collection of common UNIX utilities and programs ä Anyone who can code can make modifications to them l Impact? Marketshare? ä 25% of servers ä 2.8% of desktops [IDC 2004]

CompSci Types of software l Software Licenses ä Public domain ä Free ä Open Source ä Copylefted ä Semi-free ä Commercial l Specific licenses ä GNU Public License ä Mozilla Public License ä Lots more… l Proprietary (closed) software ä Freeware ä Shareware ä Adware ä Spyware l Commercial Academic licenses Say you buy software using (steep) student discounts that are available at the Duke Computer Store? Can you use it when you leave Duke and are no longer a student? What do you buy when you purchase software?

CompSci Open source l Commercial software license schemes ä Microsoft’s Embrace and Extend ä What’s a EULA? l Rights ä Make copies of the program and distribute them ä Access to the software’s source code ä Make improvements to the program l Results ä All contributors at same relative level ä Lots of competition in distribution or support ä Why does it work? l Free Software Foundation formed in 1984 Free Software Foundation ä GNU General Public License (Copyleft) ä Seminal work produced (emacs, gnu compiler) ä Spawned different licenses like the Open Source DefinitionOpen Source Definition

CompSci What’s special about software? l Why is there no significant "Free Hardware Movement" analogous to the Free Software Foundation's work? l What about the One Laptop per Child Project?One Laptop per Child

CompSci Emerging methods in programming l Individual vs. Group, Proprietary vs. Open source l Agile programming l Extreme programming

CompSci XP and Refactoring (See books by Kent Beck (XP) and Martin Fowler (refactoring)) l eXtreme Programming (XP) is an agile design process ä Communication: unit tests, pair programming, estimation ä Simplicity: what is the simplest approach that works? ä Feedback: system and clients; programs and stories ä Courage: throw code away, dare to be great/different l Make it run, make it right, make it fast, make it small l Do the simplest thing that can possibly work (XP)

CompSci Quotations from Fred Brooks l Plan to throw one away; you will anyhow. l Successful software always gets changed. l Good judgment comes from experience; experience comes from bad judgment l The programmer, like the poet, works only slightly removed from pure thought-stuff. He builds castles in the air, from air, creating by exertion of the imagination. Few media of creation are so flexible, so easy to polish and rework, so readily capable of realizing grand conceptual structures. Yet the program construct, unlike the poet's words, is real in the sense that it moves and works, producing visible outputs separate from the construct itself. It prints results, draws pictures, produces sounds, moves arms. The magic of myth and legend has come true in our time. One types the correct incantation on a keyboard, and a display screen comes to life, showing things that never were nor could be.... The computer resembles the magic of legend in this respect, too. If one character, one pause, of the incantation is not strictly in proper form, the magic doesn't work. Human beings are not accustomed to being perfect, and few areas of human activity demand it. Adjusting to the requirement for perfection is, I think, the most difficult part of learning to program.

CompSci Beyond software - licensing for all

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CompSci Sources of material l Organizations ä The Electronic Frontier Foundation The Electronic Frontier Foundation ä Center for Democracy and Technology Center for Democracy and Technology l Media and discussion ä Wired Magazine Wired Magazine ä Slashdot Slashdot l Databases of information and laws ä Lexis/Nexis Lexis/Nexis ä Thomas Thomas l Social issues in Computer Science ä Computer Professionals for Social Responsibility Computer Professionals for Social Responsibility