In Bilski, the Federal Circuit laid down the law of subject matter eligibility under Section 101 of the Patent Act. To be patent eligible, a claimed process must either: (1) be tied to a particular machine or apparatus, or (2) transform a particular article into a different state or thing. In all likelihood, claim limitations focused at general machines such as a "computer" will not be considered tying to "particular machine." Bilski did not, however, decide that question – Bilski's claims were admittedly divorced from any particular machine. On the transformation side, the court provided the example from Abele where graphically displaying "X-ray attenuation data produced in a two dimensional field by a computed tomography scanner" was sufficient transformation. Bilski's claims were essentially knocked-out on the new mental steps doctrine – a process where all the claimed steps "may be performed entirely in the human mind is obviously not tied to any machine and does not transform any article into a different state or thing."
Two additional points: Although the Federal Circuits points to the machine-or-transformation test as the sole test for Section 101 patentability, the court approved two ‘corollaries.’ First, field-of-use limitations continue to be “generally insufficient to render an otherwise ineligible process claim patent-eligible.” Second, "insignificant postsolution activity will not transform an unpatentable principle into a patentable process." (quoting Diehr). Thus, merely reciting a specific machine or particular transformation will not bring a claim into the realm of patentable subject matter unless the recitation is more than mere insignificant postolution or extra-solution activity.
Going forward, I do not believe that these limitations will have a significant impact on a skilled practitioner's ability to patent software innovations. However, I would like community input on how you might properly claim computer software in a way that avoids § 101 rejections?