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CompSci 001 16.1
Today’s topics
OS & SocietySoftware development models
ReadingOpen Source definitions Microsoft Corp., "Some Questions Every Business
Should Ask About the GNU General Public License (GPL)", 2001
Brookshear, Chapter 6
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OS & Software Development
1. Who writes software?
2. How are they paid for it?
How is software developed?
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UNIX: History of an OS
1969: UNIX created Private research project at Bell Labs High-level language used by system and
application developers Good programming interface Sophisticated
apps 1971: First edition released 1972: Dennis Ritchie rewrites B
What did he call the new language? 1977: Berkeley Software Design releases BSD
Unix
UNIX is ubiquitous in research institutions
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Richard Stallman’s quest
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.
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From software to politics?
Help change the world?
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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 ([email protected])
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 :-(
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Linux Timeline 10/1991 : v0.02 - first
usable Linux 01/1992 : v0.12 - first
'actually working' version, under GPL
03/1992 : comp.os.linux 04/1992 : v0.95 - capable
of using X 09/1992 : Linux stops
being Minix-like and becomes UNIX-like
03/1994 : 1.0 06/1996 : 2.0.0 12/2003 : 2.6.0
What is Linux? Freely available OS Based on Linux
kerrnel developed by Torvalds
Collection of common UNIX utilities and programs
Anyone who can code can make modifications to them
Impact? Marketshare? 25% of servers 2.8% of desktops
• [IDC 2004]
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Types of software Software Licenses
Public domain Free Open Source Copylefted Semi-free Commercial
Specific licenses GNU Public License Mozilla Public License Lots more…
Proprietary (closed) software Freeware Shareware Adware Spyware
CommercialAcademic 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?
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Open source Commercial software license schemes
Microsoft’s Embrace and Extend What’s a EULA?
Rights Make copies of the program and distribute them Access to the software’s source code Make improvements to the program
Results All contributors at same relative level Lots of competition in distribution or support Why does it work?
Free Software Foundation formed in 1984 GNU General Public License (Copyleft) Seminal work produced (emacs, gnu compiler) Spawned different licenses like the Open Source Definition
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What’s special about software?
Why is there no significant "Free Hardware Movement" analogous to the Free Software Foundation's work?
What about the One Laptop per Child Project?
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Emerging methods in programming
Individual vs. Group, Proprietary vs. Open source Agile programming
Extreme programming
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XP and Refactoring
(See books by Kent Beck (XP) and Martin Fowler (refactoring)) eXtreme Programming (XP) is an agile design process
Communication: unit tests, pair programming, estimation
Simplicity: what is the simplest approach that works?
Feedback: system and clients; programs and stories Courage: throw code away, dare to be
great/different
Make it run, make it right, make it fast, make it small Do the simplest thing that can possibly work (XP)
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Quotations from Fred Brooks Plan to throw one away; you will anyhow. Successful software always gets changed. Good judgment comes from experience; experience comes from bad
judgment
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.
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Beyond software - licensing for all
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http://creativecommons.org
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Sources of material
Organizations The Electronic Frontier Foundation Center for Democracy and Technology
Media and discussion Wired Magazine Slashdot
Databases of information and laws Lexis/Nexis Thomas
Social issues in Computer Science Computer Professionals for Social Responsibilit
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