Background
Aristocrat Technologies Australia PTY Ltd. held U.S. Patent No. 6,093,102, directed to an electronic slot machine with a configurable game controller that allowed players to select combinations of symbol positions on reels to try to match a displayed “feature” symbol. The patent’s key claims were drafted as means-plus-function limitations — a statutory claim format under 35 U.S.C. § 112, paragraph 6 (now § 112(f)) that defines a claim element by the function it performs rather than by physical structure.
International Game Technology (IGT) made competing electronic gaming machines. Aristocrat sued IGT for infringement. The district court found the patent’s means-plus-function claims invalid for indefiniteness because the specification failed to disclose adequate structure for the “game control means” limitation — the software component responsible for the slot machine’s configurable operation. Aristocrat appealed, arguing its disclosure was sufficient.
The Court’s Holding
The Federal Circuit affirmed. The court held that when a means-plus-function claim covers a computer-implemented function, the corresponding structure disclosed in the specification must be a specific algorithm — not merely a general-purpose computer or a vague reference to software. Claiming a functional result while disclosing only that “a computer does it” renders the claim indefinite because it fails to define the actual structure (the algorithm) that performs the claimed function.
The court clarified that the disclosure need not be source code or a highly detailed technical description — a functional description of the algorithm’s steps, a flowchart, or a step-by-step procedural description that would enable a person of ordinary skill to understand what the computer must do to perform the claimed function is sufficient. But Aristocrat’s specification failed even this threshold: it disclosed only that a controller runs software configured to implement the game, without describing any identifiable algorithm. The court struck a middle ground between requiring complete source code and accepting a bare reference to software — requiring at minimum an identifiable process or set of steps.
Key Takeaways
- Means-plus-function claims for computer-implemented functions must be supported by a specific algorithm in the specification — a general reference to “a programmed computer” or “software” is insufficient structure under § 112(f).
- The required algorithm disclosure need not be source code; a functional description, flowchart, or procedural steps that a skilled person could understand and implement is sufficient.
- Failure to disclose the corresponding algorithm renders a computer-implemented means-plus-function claim indefinite and therefore invalid under § 112.
- The decision established an important constraint on how software patents can claim computer-implemented functionality, with significant implications for gaming, fintech, and other computer-implemented inventions.
Why It Matters
Aristocrat Technologies v. IGT is a landmark case in the law of means-plus-function claiming for software and computer-implemented inventions. By requiring that the specification disclose the actual algorithm — not just a reference to software or a programmed computer — the Federal Circuit created a meaningful disclosure requirement that prevented patent applicants from claiming an unlimited range of computer implementations through means-plus-function language without explaining what the computer must actually do.
For the gaming and software industries, the ruling established that broad means-plus-function claims over computer-implemented functions must be grounded in real algorithmic disclosure, not vague aspirational descriptions. For patent prosecutors, it became a critical lesson in the importance of including flowcharts, step-by-step descriptions, or functional algorithms in specifications that support means-plus-function claims. The algorithm disclosure requirement remains a live issue in software patent litigation to this day.