The library goes digital

When you visit a traditional bookmobile, you leave with a stack of paperbacks and videos to schlep home. But at today's Digital Bookmobile, you'll leave armed with knowledge about downloading free books, music, and videos at home via the Internet. At the Boston Public Library event at City Hall Plaza, the main attraction is a 74-foot-long, 18-wheel tractor-trailer loaded with computers, portable media players, and real live people to show you how the process works. Bring your BPL-system library card and you can check out items today to download at home, or sign up for a card in the bookmobile. Mystery author Julia Spencer-Fleming will read at noon. 8 a.m.-3 p.m. Free. City Hall Plaza, Government Center. 617-859-2389. overdrive.bpl.org