Software: Machine Code and Programming Languages

A large program like Firefox.exe is a big block of machine code
It's very rare for a person to write machine code directly
Instead, we write code in one of many "programming languages"
- e.g. Java, Javascript, Python, C, C++

Programming Languages - In Translation

CPU machine code is the "native" language of the CPU
CPU machine code instructions are extremely simple
Hard to get much done with such simple instructions
Programming languages have "high level" features, like print
There is no single machine code instruction that prints
So how do programming languages work?
Programming languages work in translation to machine code
In Javascript, the print statement is translated to, say, 10 machine code instructions
These 10 instructions, when run, perform the print command

Two worlds...

Source Code
1. The "source code" of the program, written in a programming language (e.g. Javascript for CS101)
The source code defines the behavior of the program
A human can read and edit the source code
But source code does not "run" on the CPU directly

Machine Code
The CPU understands machine code
Only machine code can actually run on the CPU
The source code is translated to machine code, and that translation runs on the CPU
Extra for the curious:
1. The translation can be done ahead of time by a "compiler"
-e.g. Firefox source code compiled to yield Firefox.exe
2. The translation can be done on-the-fly
-This is how CS101 works
-You type Javascript source code into the browser
-It is translated at the moment you click Run

e.g. Microsoft Word
Microsoft owns and controls the source code
Microsoft sells you Word.exe and permission to run it
- You just have the machine code!
Word has lots of valuable features, and you pay Microsoft for the right to use it
The classic vendor-customer market which we all use all the time
Control: Microsoft has all the control, customer can just buy or not
Competition is what keeps companies in check in a market

Open Source Software is incredibly widespread
Computers, phones, the internet .. built with tons of open source software
Open source software is free; no vendor is paid
No $$$ -> how does this ever get written?
Aside: capitalism has many frustrating qualities
-Study open source software
-Counter to capitalism and yet super popular
Examples of open source software:
- Linux operating system
- The Android operating system (95% of it)
- Parts of Mac OS X (50%?)
- The Chrome Browser (!!!)
- The Firefox Browser
- The MySQL database system
- The GCC compiler
- Computer languages: C, C++, Python, Java, Javascript
Any computer/phone/site you use, there's lots of open-source software in the "stack"

Free Software Foundation
-1985 Richard Stallman
-A revolutionary who believed users should have the right to see/edit their software
-"Freedom" driven (more philosopher, less economist)
-(slowly) turned out to be a great model in and out of the for-profit world

Open Source software - a legal structure
(there are many variants, so this is a high-level view)
1. source code - The source code is freely available
-Typically the software does not cost anything
-It can be used in profit-making enterprises
-How does it come to exist? (see below)
2. right to modify The software includes a legal right to make modifications
-And the right to use and distribute these modifications
3. contribute back changes
-If someone adds a feature or fixes a bug in the source code
-There are incentives to contribute that change back to the shared source code
-In some licenses, conribute-back is obligatory
-There is some sort of board that decides to accept code contributions
Basically the opposite of the Proprietary-Fine-Print!
Open Source Social Contract:
-Here is great software and you are free to use and change it
-If you add a great feature, contribute it back so others may use it

The Chrome browser is open source, therefore you could...
1. Download the chrome source code ("chromium")
2. Modify the source code so every page it displays says "Beat Cal" at the top
3. Distribute your new version of "Chrome"
-You'd have to call it something else ... Chrome is trademarked
4. For a real feature, you might contribute the change back to the main Chrome source code
Key: you have control, not the vendor

GCC is a widely used "compiler"
An important and very complicated piece of software infrastructure
Aside: a compiler translates source code into runnable machine code
GCC is open source under the GPL open source license
1. Free GCC costs no money to use, just download it
2. Source code The source code of GCC is available
- fix a bug or add a feature you want to GCC
3. Contribute there are incentives to contribute changes back to the main GCC source code

i.e. How does open source software come to exist?
Apple, Google, Facebook, Redhat, Oracle, Twitter all use GCC
Some of these companies are competitors
Many of them contribute bug fixes, features back to GCC
-They fix the bug because they want it fixed for themselves first
-But the contributions then flow to all, including their competitors

So what is the result...

How open source gets picked up by Apple, Google, ...
They need something like GCC infrastructure to exist
They all use GCC
They all contribute to GCC
The benefits of the contributions will flow to all (competitors)
Therefore
1. We all get the benefit of free, high quality infrastructure piece
2. BUT nobody is going to have competitive advantage from GCC
Result:
-GCC is a free infrastructure piece
-Maintained and used by all
-Not a source of competitive advantage ("cudgel")

Software has many layers where you want something to work reliably
Open source provides
-free
-widely used, high quality
-maintained collectively
-provides no advantage vs. competitors
Conclusion: for many niches, free + high-quality is an appealing tradeoff
Proprietary software is not dead, but open source dominates many areas
Ultimately we all benefit: avoid work duplication
That's how your computer systems work today!