Tonight, I suggest reading Professor Dennis Crouch's Rise of Computer Patents.
Professor Crouch says it's difficult to define "software patents," but has a graph that indicates US patents with an independent computing claim (i.e., reciting "computer, processor, software, machine readable, information, memory, data, virtual, or storage media") increased from about 5% in 1976 to 35% in 2014. The graph also shows 40% of US patent will include an independent computing claim in 2015, but it's not clear how this can be determined.
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