With some maneuvering, he and Tron take over the MCP and kill Sark, proving they're the most badass guys in the mainframe.
Just like he was lasered into the mainframe, Flynn is beamed out, with proof that Dillinger stole the videogames he invented.
Since the poem was written, the darker side of personal and mainframe computers has given the poem a more sinister meaning.
A large, often powerful computer, usually dedicated to lengthy, complex calculations or set up for use by many people simultaneously. Compare personal computer.