Maino’s music spread originally via tapes in prison. Boing Boing commentors foresee a future where prisoners use SD cards instead of tape. via (via NYtimes)

More than 2.3 million people were locked up in federal, state or local systems at midyear 2007, according to the U.S. Dept. of Justice, and they want their Michael Jackson and Pink Floyd just like everyone else.

Enter North Hollywood-based Pack Central, which runs a mail-order operation for about 50,000 prisoners. It stocks about 10,000 CDs and 5,000 cassette titles.

Cassettes account for about 60% of unit sales, since CDs are contraband in many prisons because the hard plastics can be used for nefarious means. The screws that hold many cassettes together are also verboten, so owner Bob Paris must manually remove them. A bigger problem is that the labels have largely abandoned cassettes.

Best-selling current titles include Lil Wayne’s “Tha Carter III,” Mariah Carey’s “E=MC2,” Usher’s “Here I Stand,” Rihanna’s “Good Girl Gone Bad,” Nickelback’s “All the Right Reasons,” Leona Lewis’ “Spirit” and Lyfe Jennings’ “Life Change.”

Perennial sellers include Al Green’s “Greatest Hits,” Linkin Park’s “Hybrid Theory,” Michael Jackson’s “Thriller,” Pink Floyd’s “The Dark Side of the Moon” and a best-of collection by the Stylistics.