Diamond v. Diehr ruling by US Supreme Court on 3 March 1981
Diamond v. Diehr, 450 U.S. 175, 192 (1981) is the last case where the Supreme Court of the USA ruled on the definition of patentable subject matter.
At issue in this case is a system for curing rubber with the aid of a computer and some mathematical formulas. The Supreme Court upheld the patent and this ruling is generally seen as increasing the scope for the patenting of software.
Others, such as Ben Klemens, argue that the ruling confirms that software ideas are not patentable. (See ESP's 2008 Bilski amicus brief)
The ruling also confirms that "excluded from such patent protection are ... abstract ideas.".
Excerpts
insignificant postsolution activity will not transform [450 U.S. 175, 192] an unpatentable principle into a patentable process. Ibid. 14 To hold otherwise would allow a competent draftsman to evade the recognized limitations on the type of subject matter eligible for patent protection. On the other hand, when a claim containing a mathematical formula implements or applies that formula in a structure or process which, when considered as a whole, is performing a function which the patent laws were designed to protect (e. g., transforming or reducing an article to a different state or thing), then the claim satisfies the requirements of 101.
Note that the "whole" is an algorithm plus a structure/process which, for example, transforms an article to a different state or thing. However, the CAFC has used the "as a whole" doctrine to allow pure software patents which include no such transformation.
