I know Data's brain is 'positronic', but what does that mean? It was invented by Asimov, right? Sometimes they talk about creating new connections, such as in an organic network, but other times they talk about running subroutines. Just wondering if there is more data (hehe) about this AI technology.
In reality, "positronic" means almost absolutely nothing; it's pure fiction first written about by Isaac Asimov in his books about robots. The word comes from the discovery of the positron which was a popular science point when they were written.
Positronic in the Star Trek universe means that the robotic brain resembles that of one with consciousness, so the brain may be robotic, but it will have some humane qualities to it. As far as talking about neural pathways and subroutines, the human brain does those things and the positronic one would mimic the way that the human brain would do it and in some ways, it would be faster, easier or better, depending on the circumstances.
Fuzzy explains "positronic" well, so I will concentrate on its capabilities as described on the show.
Data's capacity is stated in terms of operations per second, gigaquads of data storage and so forth. He apparently has peripheral devices like an internal chronometer. This seems to imply that he has software somewhat like a modern computer, but he doesn't seem to have the ability to interface directly with other machines. If he memory was like a hard disk with software to retrieve specific data it would stand to reason that he could download, say, video from his eyes and show it to other people.
Similarly Data talks about "subroutines", but no-one ever writes one for him.
So it seems that Data's brain is some kind of hybrid device, and when people talk about its computational or storage capacity they are just making a flawed by useful comparison to other machines. Subroutines could be akin to lobes of the human brain, or simply an assignment of resources within it (like an FPGA that consists of lots of identical parts that can be dynamically assigned to different tasks).
Data's brain appears to be a transcendental object. Talk about sub-routines is a writing device to try to explain the (currently) unexplainable. The terminology is a lift from Asimov. This really defies explanation and like a lot of science fiction requires suspense of belief.
At best we are looking at a massively parallel structure similar to the human brain and I believe it should be let go at that. In one of the episodes, a scientist attempted to sequester Data for close examination, but the episode finishes by proving that Data is a self-aware being who need not volunteer to be disassembled for someone's curiosity.