🚀 go-pugleaf

In article <1991Feb27.231511.19935@digibd.com> rhealey@digibd.com (Rob Healey) writes:
	   The concept of backing store strikes me as being something that
	   could have easily been prior art, but only AT&T bothered to
	   patent it? Are there any examples of backing store before 1985?

The answer is in "Against Software Patents", a position paper by the League
for Programming Freedom.  The relevant excerpt appears below.

Write to league@prep.ai.mit.edu for membership info.

					-Michael Ernst
					 mernst@theory.lcs.mit.edu

===========================================================================

@heading Patenting What Is Too Obvious to Publish

Sometimes it is possible to patent a technique that is not new precisely
because it is obvious---so obvious that no one would have published a
paper about it.

For example, computer companies distributing the free X Window System
developed by MIT are now being threatened with lawsuits by AT&T over
patent number 4,555,775, covering the use of ``backing store.''  This
technique is used when there are overlapping windows; the contents of a
window that is partly hidden are saved in off-screen memory, so they can
be put back quickly on the screen if the obscuring window disappears (as
often happens).

The technique of backing store was used in an earlier MIT project, the
Lisp Machine System, before AT&T applied for the patent.  The Lisp
Machine developers published nothing about this detail at the time,
considering it too obvious.  It was mentioned years later when the
programmers' reference manual explained how to turn it on and off.

The Lisp Machine was the first computer to use this technique only
because it had a larger memory than earlier machines that had window
systems.  Prior window system developers must have dismissed the idea
because their machines had insufficient memory space to spare any for
this purpose.  Improvements in memory chips made development of backing
store inevitable.

Without a publication, the use of backing store in the Lisp Machine
System may not count as prior art to defeat the patent.  So the AT&T
patent may stand, and MIT may be forbidden to continue using a method
that MIT used before AT&T.

The result is that the dozens of companies and hundreds of thousands of
users who accepted the software from MIT on the understanding that it
was free are now faced with possible lawsuits.  (They are also being
threatened with Cadtrak's exclusive-or patent.)  The X Window System
project was intended to develop a window system that all developers
could use freely.  This public service goal seems to have been thwarted
by patents.