Credit: Harry Campbell

No one would buy a car with the hood welded shut, but that is essentially what commercial software is. However, since computing began, some software has been distributed in such a way that users can change or repair it by modifying its source code--the step-by-step instructions that the computer executes when the software runs. Software distributed under a license that allows a programmer to modify the source code and freely distribute an improved version of it is called open source.

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