How long from when the code is 1st written or distributed, until GPL Copyrighted material falls into public domain, in the United States?
I'm guessing 120 years, but I'm not a lawyer.
Also how has this(GPL'ed software copyright duration) changed if any over the years?
Please Elaborate and Clarify my understanding.
Hope this link will give you a good idea on GPL licensing -
http://en.wikipedia.org/wiki/GNU_General_Public_License
Also taken from this link -
"Convey the object code in, or embodied in, a physical product (including a physical distribution medium), accompanied by a written offer, valid for at least three years and valid for as long as you offer spare parts or customer support for that product model, to give anyone who possesses the object code either (1) a copy of the Corresponding Source for all the software in the product that is covered by this License, on a durable physical medium customarily used for software interchange, for a price no more than your reasonable cost of physically performing this conveying of source, or (2) access to copy the Corresponding Source from a network server at no charge."
GPL copyright is no different than any other copyright in this regard. Current copyright law in the U.S. is life of the author plus 70 years (or life of the last surviving author plus 70 years, for multiple authors); or, for works for hire, 95 years from publication, or 120 years from creation, whichever is shorter.
As a practical matter, Disney and others would stand to lose a great deal from their works entering the public domain and have successfully lobbied to extend copyright in the past in order to prevent this, so it's possible that copyright protection will continue to be extended indefinitely.
Disclaimer: I'm not a lawyer.
The GPL and copyright are two different concepts, and need to be treated as such.
The GPL is a license, and dictates how you may use a piece of code for so long as the owner has the right to enforce a license on it - that is, while the code is protected by the owner's copyright. Thus, the GPL never expires, but once copyright expires, the owner no longer has licensing control over the code, and the code could then be re-licensed by any member of the public without the GPL.
By way of illustration, I might create a piece of code, which I then own the copyright on, but I can choose to publish it under a public domain license, which grants anyone the ability to use my code under the authority of my copyright.
Copyright, in the United States, is automatically granted to the creator of an artistic or creative work upon creation of the work. Per Wikipedia, "The [Copyright Term Extension] Act extended these terms to life of the author plus 70 years and for works of corporate authorship to 120 years after creation or 95 years after publication, whichever endpoint is earlier.", so yes, copyright can last up to 120 years in the case of code under corporate authorship. Wikipedia has a full list of changes to the term of copyright in the United States.
There is not a 'GPL' copyright. There is copyright, full stop, and it's indipendent of the terms and conditions of (eventual) distribution.
Look at wikipedia for the history of copyright and the actual state of US copyright.
Alse, remember that copyright arises when an idea is transposed into a tangible form (e.g. first written down), no matter if published or not.
For a collective work - like an open source unit of software - be aware that each modification of the original or addition to it might well be itself copyrighted.