Traditionalists may look aghast at CS50, Harvard’s introductory computer science course, which last year became the school’s most popular course of any kind. It’s taught by a young professor in jeans and a black T-shirt, David Malan, whose lectures are highly polished, fast-paced performances filled with props, demonstrations, and student involvement. Students aren’t required to attend, though; lectures are recorded in a slick, multi-camera format with production values that rival commercial TV, and most students watch them online. In addition to being Harvard’s No. 1 course, it’s offered simultaneously at Yale, with Malan teaching, an arrangement apparently unprecedented in the rival schools’ 318-year coexistence.